compiler/rustc_const_eval/src/interpret/validity.rs

   1 //! Check the validity invariant of a given value, and tell the user
   2 //! where in the value it got violated.
   3 //! In const context, this goes even further and tries to approximate const safety.
   4 //! That's useful because it means other passes (e.g. promotion) can rely on `const`s
   5 //! to be const-safe.
   6
   7 use std::convert::TryFrom;
   8 use std::fmt::Write;
   9 use std::num::NonZeroUsize;
  10
  11 use rustc_data_structures::fx::FxHashSet;
  12 use rustc_hir as hir;
  13 use rustc_middle::mir::interpret::InterpError;
  14 use rustc_middle::ty;
  15 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
  16 use rustc_span::symbol::{sym, Symbol};
  17 use rustc_span::DUMMY_SP;
  18 use rustc_target::abi::{Abi, Scalar as ScalarAbi, Size, VariantIdx, Variants, WrappingRange};
  19
  20 use std::hash::Hash;
  21
  22 use super::{
  23     alloc_range, CheckInAllocMsg, GlobalAlloc, InterpCx, InterpResult, MPlaceTy, Machine,
  24     MemPlaceMeta, OpTy, ScalarMaybeUninit, ValueVisitor,
  25 };
  26
  27 macro_rules! throw_validation_failure {
  28     ($where:expr, { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )?) => {{
  29         let mut msg = String::new();
  30         msg.push_str("encountered ");
  31         write!(&mut msg, $($what_fmt),+).unwrap();
  32         $(
  33             msg.push_str(", but expected ");
  34             write!(&mut msg, $($expected_fmt),+).unwrap();
  35         )?
  36         let path = rustc_middle::ty::print::with_no_trimmed_paths(|| {
  37             let where_ = &$where;
  38             if !where_.is_empty() {
  39                 let mut path = String::new();
  40                 write_path(&mut path, where_);
  41                 Some(path)
  42             } else {
  43                 None
  44             }
  45         });
  46         throw_ub!(ValidationFailure { path, msg })
  47     }};
  48 }
  49
  50 /// If $e throws an error matching the pattern, throw a validation failure.
  51 /// Other errors are passed back to the caller, unchanged -- and if they reach the root of
  52 /// the visitor, we make sure only validation errors and `InvalidProgram` errors are left.
  53 /// This lets you use the patterns as a kind of validation list, asserting which errors
  54 /// can possibly happen:
  55 ///
  56 /// ```
  57 /// let v = try_validation!(some_fn(), some_path, {
  58 ///     Foo | Bar | Baz => { "some failure" },
  59 /// });
  60 /// ```
  61 ///
  62 /// An additional expected parameter can also be added to the failure message:
  63 ///
  64 /// ```
  65 /// let v = try_validation!(some_fn(), some_path, {
  66 ///     Foo | Bar | Baz => { "some failure" } expected { "something that wasn't a failure" },
  67 /// });
  68 /// ```
  69 ///
  70 /// An additional nicety is that both parameters actually take format args, so you can just write
  71 /// the format string in directly:
  72 ///
  73 /// ```
  74 /// let v = try_validation!(some_fn(), some_path, {
  75 ///     Foo | Bar | Baz => { "{:?}", some_failure } expected { "{}", expected_value },
  76 /// });
  77 /// ```
  78 ///
  79 macro_rules! try_validation {
  80     ($e:expr, $where:expr,
  81     $( $( $p:pat_param )|+ => { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? ),+ $(,)?
  82     ) => {{
  83         match $e {
  84             Ok(x) => x,
  85             // We catch the error and turn it into a validation failure. We are okay with
  86             // allocation here as this can only slow down builds that fail anyway.
  87             Err(e) => match e.kind() {
  88                 $(
  89                     $($p)|+ =>
  90                        throw_validation_failure!(
  91                             $where,
  92                             { $( $what_fmt ),+ } $( expected { $( $expected_fmt ),+ } )?
  93                         )
  94                 ),+,
  95                 #[allow(unreachable_patterns)]
  96                 _ => Err::<!, _>(e)?,
  97             }
  98         }
  99     }};
 100 }
 101
 102 /// We want to show a nice path to the invalid field for diagnostics,
 103 /// but avoid string operations in the happy case where no error happens.
 104 /// So we track a `Vec<PathElem>` where `PathElem` contains all the data we
 105 /// need to later print something for the user.
 106 #[derive(Copy, Clone, Debug)]
 107 pub enum PathElem {
 108     Field(Symbol),
 109     Variant(Symbol),
 110     GeneratorState(VariantIdx),
 111     CapturedVar(Symbol),
 112     ArrayElem(usize),
 113     TupleElem(usize),
 114     Deref,
 115     EnumTag,
 116     GeneratorTag,
 117     DynDowncast,
 118 }
 119
 120 /// Extra things to check for during validation of CTFE results.
 121 pub enum CtfeValidationMode {
 122     /// Regular validation, nothing special happening.
 123     Regular,
 124     /// Validation of a `const`.
 125     /// `inner` says if this is an inner, indirect allocation (as opposed to the top-level const
 126     /// allocation). Being an inner allocation makes a difference because the top-level allocation
 127     /// of a `const` is copied for each use, but the inner allocations are implicitly shared.
 128     /// `allow_static_ptrs` says if pointers to statics are permitted (which is the case for promoteds in statics).
 129     Const { inner: bool, allow_static_ptrs: bool },
 130 }
 131
 132 /// State for tracking recursive validation of references
 133 pub struct RefTracking<T, PATH = ()> {
 134     pub seen: FxHashSet<T>,
 135     pub todo: Vec<(T, PATH)>,
 136 }
 137
 138 impl<T: Copy + Eq + Hash + std::fmt::Debug, PATH: Default> RefTracking<T, PATH> {
 139     pub fn empty() -> Self {
 140         RefTracking { seen: FxHashSet::default(), todo: vec![] }
 141     }
 142     pub fn new(op: T) -> Self {
 143         let mut ref_tracking_for_consts =
 144             RefTracking { seen: FxHashSet::default(), todo: vec![(op, PATH::default())] };
 145         ref_tracking_for_consts.seen.insert(op);
 146         ref_tracking_for_consts
 147     }
 148
 149     pub fn track(&mut self, op: T, path: impl FnOnce() -> PATH) {
 150         if self.seen.insert(op) {
 151             trace!("Recursing below ptr {:#?}", op);
 152             let path = path();
 153             // Remember to come back to this later.
 154             self.todo.push((op, path));
 155         }
 156     }
 157 }
 158
 159 /// Format a path
 160 fn write_path(out: &mut String, path: &[PathElem]) {
 161     use self::PathElem::*;
 162
 163     for elem in path.iter() {
 164         match elem {
 165             Field(name) => write!(out, ".{}", name),
 166             EnumTag => write!(out, ".<enum-tag>"),
 167             Variant(name) => write!(out, ".<enum-variant({})>", name),
 168             GeneratorTag => write!(out, ".<generator-tag>"),
 169             GeneratorState(idx) => write!(out, ".<generator-state({})>", idx.index()),
 170             CapturedVar(name) => write!(out, ".<captured-var({})>", name),
 171             TupleElem(idx) => write!(out, ".{}", idx),
 172             ArrayElem(idx) => write!(out, "[{}]", idx),
 173             // `.<deref>` does not match Rust syntax, but it is more readable for long paths -- and
 174             // some of the other items here also are not Rust syntax.  Actually we can't
 175             // even use the usual syntax because we are just showing the projections,
 176             // not the root.
 177             Deref => write!(out, ".<deref>"),
 178             DynDowncast => write!(out, ".<dyn-downcast>"),
 179         }
 180         .unwrap()
 181     }
 182 }
 183
 184 // Formats such that a sentence like "expected something {}" to mean
 185 // "expected something <in the given range>" makes sense.
 186 fn wrapping_range_format(r: WrappingRange, max_hi: u128) -> String {
 187     let WrappingRange { start: lo, end: hi } = r;
 188     assert!(hi <= max_hi);
 189     if lo > hi {
 190         format!("less or equal to {}, or greater or equal to {}", hi, lo)
 191     } else if lo == hi {
 192         format!("equal to {}", lo)
 193     } else if lo == 0 {
 194         assert!(hi < max_hi, "should not be printing if the range covers everything");
 195         format!("less or equal to {}", hi)
 196     } else if hi == max_hi {
 197         assert!(lo > 0, "should not be printing if the range covers everything");
 198         format!("greater or equal to {}", lo)
 199     } else {
 200         format!("in the range {:?}", r)
 201     }
 202 }
 203
 204 struct ValidityVisitor<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> {
 205     /// The `path` may be pushed to, but the part that is present when a function
 206     /// starts must not be changed!  `visit_fields` and `visit_array` rely on
 207     /// this stack discipline.
 208     path: Vec<PathElem>,
 209     ref_tracking: Option<&'rt mut RefTracking<MPlaceTy<'tcx, M::PointerTag>, Vec<PathElem>>>,
 210     /// `None` indicates this is not validating for CTFE (but for runtime).
 211     ctfe_mode: Option<CtfeValidationMode>,
 212     ecx: &'rt InterpCx<'mir, 'tcx, M>,
 213 }
 214
 215 impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, 'tcx, M> {
 216     fn aggregate_field_path_elem(&mut self, layout: TyAndLayout<'tcx>, field: usize) -> PathElem {
 217         // First, check if we are projecting to a variant.
 218         match layout.variants {
 219             Variants::Multiple { tag_field, .. } => {
 220                 if tag_field == field {
 221                     return match layout.ty.kind() {
 222                         ty::Adt(def, ..) if def.is_enum() => PathElem::EnumTag,
 223                         ty::Generator(..) => PathElem::GeneratorTag,
 224                         _ => bug!("non-variant type {:?}", layout.ty),
 225                     };
 226                 }
 227             }
 228             Variants::Single { .. } => {}
 229         }
 230
 231         // Now we know we are projecting to a field, so figure out which one.
 232         match layout.ty.kind() {
 233             // generators and closures.
 234             ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 235                 let mut name = None;
 236                 // FIXME this should be more descriptive i.e. CapturePlace instead of CapturedVar
 237                 // https://github.com/rust-lang/project-rfc-2229/issues/46
 238                 if let Some(local_def_id) = def_id.as_local() {
 239                     let tables = self.ecx.tcx.typeck(local_def_id);
 240                     if let Some(captured_place) =
 241                         tables.closure_min_captures_flattened(*def_id).nth(field)
 242                     {
 243                         // Sometimes the index is beyond the number of upvars (seen
 244                         // for a generator).
 245                         let var_hir_id = captured_place.get_root_variable();
 246                         let node = self.ecx.tcx.hir().get(var_hir_id);
 247                         if let hir::Node::Binding(pat) = node {
 248                             if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
 249                                 name = Some(ident.name);
 250                             }
 251                         }
 252                     }
 253                 }
 254
 255                 PathElem::CapturedVar(name.unwrap_or_else(|| {
 256                     // Fall back to showing the field index.
 257                     sym::integer(field)
 258                 }))
 259             }
 260
 261             // tuples
 262             ty::Tuple(_) => PathElem::TupleElem(field),
 263
 264             // enums
 265             ty::Adt(def, ..) if def.is_enum() => {
 266                 // we might be projecting *to* a variant, or to a field *in* a variant.
 267                 match layout.variants {
 268                     Variants::Single { index } => {
 269                         // Inside a variant
 270                         PathElem::Field(def.variants[index].fields[field].name)
 271                     }
 272                     Variants::Multiple { .. } => bug!("we handled variants above"),
 273                 }
 274             }
 275
 276             // other ADTs
 277             ty::Adt(def, _) => PathElem::Field(def.non_enum_variant().fields[field].name),
 278
 279             // arrays/slices
 280             ty::Array(..) | ty::Slice(..) => PathElem::ArrayElem(field),
 281
 282             // dyn traits
 283             ty::Dynamic(..) => PathElem::DynDowncast,
 284
 285             // nothing else has an aggregate layout
 286             _ => bug!("aggregate_field_path_elem: got non-aggregate type {:?}", layout.ty),
 287         }
 288     }
 289
 290     fn with_elem<R>(
 291         &mut self,
 292         elem: PathElem,
 293         f: impl FnOnce(&mut Self) -> InterpResult<'tcx, R>,
 294     ) -> InterpResult<'tcx, R> {
 295         // Remember the old state
 296         let path_len = self.path.len();
 297         // Record new element
 298         self.path.push(elem);
 299         // Perform operation
 300         let r = f(self)?;
 301         // Undo changes
 302         self.path.truncate(path_len);
 303         // Done
 304         Ok(r)
 305     }
 306
 307     fn check_wide_ptr_meta(
 308         &mut self,
 309         meta: MemPlaceMeta<M::PointerTag>,
 310         pointee: TyAndLayout<'tcx>,
 311     ) -> InterpResult<'tcx> {
 312         let tail = self.ecx.tcx.struct_tail_erasing_lifetimes(pointee.ty, self.ecx.param_env);
 313         match tail.kind() {
 314             ty::Dynamic(..) => {
 315                 let vtable = self.ecx.scalar_to_ptr(meta.unwrap_meta());
 316                 // Direct call to `check_ptr_access_align` checks alignment even on CTFE machines.
 317                 try_validation!(
 318                     self.ecx.memory.check_ptr_access_align(
 319                         vtable,
 320                         3 * self.ecx.tcx.data_layout.pointer_size, // drop, size, align
 321                         self.ecx.tcx.data_layout.pointer_align.abi,
 322                         CheckInAllocMsg::InboundsTest, // will anyway be replaced by validity message
 323                     ),
 324                     self.path,
 325                     err_ub!(DanglingIntPointer(..)) |
 326                     err_ub!(PointerUseAfterFree(..)) =>
 327                         { "dangling vtable pointer in wide pointer" },
 328                     err_ub!(AlignmentCheckFailed { .. }) =>
 329                         { "unaligned vtable pointer in wide pointer" },
 330                     err_ub!(PointerOutOfBounds { .. }) =>
 331                         { "too small vtable" },
 332                 );
 333                 try_validation!(
 334                     self.ecx.read_drop_type_from_vtable(vtable),
 335                     self.path,
 336                     err_ub!(DanglingIntPointer(..)) |
 337                     err_ub!(InvalidFunctionPointer(..)) =>
 338                         { "invalid drop function pointer in vtable (not pointing to a function)" },
 339                     err_ub!(InvalidVtableDropFn(..)) =>
 340                         { "invalid drop function pointer in vtable (function has incompatible signature)" },
 341                 );
 342                 try_validation!(
 343                     self.ecx.read_size_and_align_from_vtable(vtable),
 344                     self.path,
 345                     err_ub!(InvalidVtableSize) =>
 346                         { "invalid vtable: size is bigger than largest supported object" },
 347                     err_ub!(InvalidVtableAlignment(msg)) =>
 348                         { "invalid vtable: alignment {}", msg },
 349                     err_unsup!(ReadPointerAsBytes) => { "invalid size or align in vtable" },
 350                 );
 351                 // FIXME: More checks for the vtable.
 352             }
 353             ty::Slice(..) | ty::Str => {
 354                 let _len = try_validation!(
 355                     meta.unwrap_meta().to_machine_usize(self.ecx),
 356                     self.path,
 357                     err_unsup!(ReadPointerAsBytes) => { "non-integer slice length in wide pointer" },
 358                 );
 359                 // We do not check that `len * elem_size <= isize::MAX`:
 360                 // that is only required for references, and there it falls out of the
 361                 // "dereferenceable" check performed by Stacked Borrows.
 362             }
 363             ty::Foreign(..) => {
 364                 // Unsized, but not wide.
 365             }
 366             _ => bug!("Unexpected unsized type tail: {:?}", tail),
 367         }
 368
 369         Ok(())
 370     }
 371
 372     /// Check a reference or `Box`.
 373     fn check_safe_pointer(
 374         &mut self,
 375         value: &OpTy<'tcx, M::PointerTag>,
 376         kind: &str,
 377     ) -> InterpResult<'tcx> {
 378         let value = try_validation!(
 379             self.ecx.read_immediate(value),
 380             self.path,
 381             err_unsup!(ReadPointerAsBytes) => { "part of a pointer" } expected { "a proper pointer or integer value" },
 382         );
 383         // Handle wide pointers.
 384         // Check metadata early, for better diagnostics
 385         let place = try_validation!(
 386             self.ecx.ref_to_mplace(&value),
 387             self.path,
 388             err_ub!(InvalidUninitBytes(None)) => { "uninitialized {}", kind },
 389         );
 390         if place.layout.is_unsized() {
 391             self.check_wide_ptr_meta(place.meta, place.layout)?;
 392         }
 393         // Make sure this is dereferenceable and all.
 394         let size_and_align = try_validation!(
 395             self.ecx.size_and_align_of_mplace(&place),
 396             self.path,
 397             err_ub!(InvalidMeta(msg)) => { "invalid {} metadata: {}", kind, msg },
 398         );
 399         let (size, align) = size_and_align
 400             // for the purpose of validity, consider foreign types to have
 401             // alignment and size determined by the layout (size will be 0,
 402             // alignment should take attributes into account).
 403             .unwrap_or_else(|| (place.layout.size, place.layout.align.abi));
 404         // Direct call to `check_ptr_access_align` checks alignment even on CTFE machines.
 405         try_validation!(
 406             self.ecx.memory.check_ptr_access_align(
 407                 place.ptr,
 408                 size,
 409                 align,
 410                 CheckInAllocMsg::InboundsTest, // will anyway be replaced by validity message
 411             ),
 412             self.path,
 413             err_ub!(AlignmentCheckFailed { required, has }) =>
 414                 {
 415                     "an unaligned {} (required {} byte alignment but found {})",
 416                     kind,
 417                     required.bytes(),
 418                     has.bytes()
 419                 },
 420             err_ub!(DanglingIntPointer(0, _)) =>
 421                 { "a null {}", kind },
 422             err_ub!(DanglingIntPointer(i, _)) =>
 423                 { "a dangling {} (address 0x{:x} is unallocated)", kind, i },
 424             err_ub!(PointerOutOfBounds { .. }) =>
 425                 { "a dangling {} (going beyond the bounds of its allocation)", kind },
 426             // This cannot happen during const-eval (because interning already detects
 427             // dangling pointers), but it can happen in Miri.
 428             err_ub!(PointerUseAfterFree(..)) =>
 429                 { "a dangling {} (use-after-free)", kind },
 430         );
 431         // Recursive checking
 432         if let Some(ref mut ref_tracking) = self.ref_tracking {
 433             // Proceed recursively even for ZST, no reason to skip them!
 434             // `!` is a ZST and we want to validate it.
 435             // Skip validation entirely for some external statics
 436             if let Ok((alloc_id, _offset, _ptr)) = self.ecx.memory.ptr_try_get_alloc(place.ptr) {
 437                 // not a ZST
 438                 let alloc_kind = self.ecx.tcx.get_global_alloc(alloc_id);
 439                 if let Some(GlobalAlloc::Static(did)) = alloc_kind {
 440                     assert!(!self.ecx.tcx.is_thread_local_static(did));
 441                     assert!(self.ecx.tcx.is_static(did));
 442                     if matches!(
 443                         self.ctfe_mode,
 444                         Some(CtfeValidationMode::Const { allow_static_ptrs: false, .. })
 445                     ) {
 446                         // See const_eval::machine::MemoryExtra::can_access_statics for why
 447                         // this check is so important.
 448                         // This check is reachable when the const just referenced the static,
 449                         // but never read it (so we never entered `before_access_global`).
 450                         throw_validation_failure!(self.path,
 451                             { "a {} pointing to a static variable", kind }
 452                         );
 453                     }
 454                     // We skip checking other statics. These statics must be sound by
 455                     // themselves, and the only way to get broken statics here is by using
 456                     // unsafe code.
 457                     // The reasons we don't check other statics is twofold. For one, in all
 458                     // sound cases, the static was already validated on its own, and second, we
 459                     // trigger cycle errors if we try to compute the value of the other static
 460                     // and that static refers back to us.
 461                     // We might miss const-invalid data,
 462                     // but things are still sound otherwise (in particular re: consts
 463                     // referring to statics).
 464                     return Ok(());
 465                 }
 466             }
 467             let path = &self.path;
 468             ref_tracking.track(place, || {
 469                 // We need to clone the path anyway, make sure it gets created
 470                 // with enough space for the additional `Deref`.
 471                 let mut new_path = Vec::with_capacity(path.len() + 1);
 472                 new_path.clone_from(path);
 473                 new_path.push(PathElem::Deref);
 474                 new_path
 475             });
 476         }
 477         Ok(())
 478     }
 479
 480     fn read_scalar(
 481         &self,
 482         op: &OpTy<'tcx, M::PointerTag>,
 483     ) -> InterpResult<'tcx, ScalarMaybeUninit<M::PointerTag>> {
 484         Ok(try_validation!(
 485             self.ecx.read_scalar(op),
 486             self.path,
 487             err_unsup!(ReadPointerAsBytes) => { "(potentially part of) a pointer" } expected { "plain (non-pointer) bytes" },
 488         ))
 489     }
 490
 491     /// Check if this is a value of primitive type, and if yes check the validity of the value
 492     /// at that type.  Return `true` if the type is indeed primitive.
 493     fn try_visit_primitive(
 494         &mut self,
 495         value: &OpTy<'tcx, M::PointerTag>,
 496     ) -> InterpResult<'tcx, bool> {
 497         // Go over all the primitive types
 498         let ty = value.layout.ty;
 499         match ty.kind() {
 500             ty::Bool => {
 501                 let value = self.read_scalar(value)?;
 502                 try_validation!(
 503                     value.to_bool(),
 504                     self.path,
 505                     err_ub!(InvalidBool(..)) | err_ub!(InvalidUninitBytes(None)) =>
 506                         { "{}", value } expected { "a boolean" },
 507                 );
 508                 Ok(true)
 509             }
 510             ty::Char => {
 511                 let value = self.read_scalar(value)?;
 512                 try_validation!(
 513                     value.to_char(),
 514                     self.path,
 515                     err_ub!(InvalidChar(..)) | err_ub!(InvalidUninitBytes(None)) =>
 516                         { "{}", value } expected { "a valid unicode scalar value (in `0..=0x10FFFF` but not in `0xD800..=0xDFFF`)" },
 517                 );
 518                 Ok(true)
 519             }
 520             ty::Float(_) | ty::Int(_) | ty::Uint(_) => {
 521                 let value = self.read_scalar(value)?;
 522                 // NOTE: Keep this in sync with the array optimization for int/float
 523                 // types below!
 524                 if M::enforce_number_validity(self.ecx) {
 525                     // Integers/floats in CTFE: Must be scalar bits, pointers are dangerous
 526                     let is_bits = value.check_init().map_or(false, |v| v.try_to_int().is_ok());
 527                     if !is_bits {
 528                         throw_validation_failure!(self.path,
 529                             { "{}", value } expected { "initialized plain (non-pointer) bytes" }
 530                         )
 531                     }
 532                 }
 533                 Ok(true)
 534             }
 535             ty::RawPtr(..) => {
 536                 // We are conservative with uninit for integers, but try to
 537                 // actually enforce the strict rules for raw pointers (mostly because
 538                 // that lets us re-use `ref_to_mplace`).
 539                 let place = try_validation!(
 540                     self.ecx.read_immediate(value).and_then(|ref i| self.ecx.ref_to_mplace(i)),
 541                     self.path,
 542                     err_ub!(InvalidUninitBytes(None)) => { "uninitialized raw pointer" },
 543                     err_unsup!(ReadPointerAsBytes) => { "part of a pointer" } expected { "a proper pointer or integer value" },
 544                 );
 545                 if place.layout.is_unsized() {
 546                     self.check_wide_ptr_meta(place.meta, place.layout)?;
 547                 }
 548                 Ok(true)
 549             }
 550             ty::Ref(_, ty, mutbl) => {
 551                 if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { .. }))
 552                     && *mutbl == hir::Mutability::Mut
 553                 {
 554                     // A mutable reference inside a const? That does not seem right (except if it is
 555                     // a ZST).
 556                     let layout = self.ecx.layout_of(*ty)?;
 557                     if !layout.is_zst() {
 558                         throw_validation_failure!(self.path, { "mutable reference in a `const`" });
 559                     }
 560                 }
 561                 self.check_safe_pointer(value, "reference")?;
 562                 Ok(true)
 563             }
 564             ty::Adt(def, ..) if def.is_box() => {
 565                 self.check_safe_pointer(value, "box")?;
 566                 Ok(true)
 567             }
 568             ty::FnPtr(_sig) => {
 569                 let value = try_validation!(
 570                     self.ecx.read_immediate(value),
 571                     self.path,
 572                     err_unsup!(ReadPointerAsBytes) => { "part of a pointer" } expected { "a proper pointer or integer value" },
 573                 );
 574                 // Make sure we print a `ScalarMaybeUninit` (and not an `ImmTy`) in the error
 575                 // message below.
 576                 let value = value.to_scalar_or_uninit();
 577                 let _fn = try_validation!(
 578                     value.check_init().and_then(|ptr| self.ecx.memory.get_fn(self.ecx.scalar_to_ptr(ptr))),
 579                     self.path,
 580                     err_ub!(DanglingIntPointer(..)) |
 581                     err_ub!(InvalidFunctionPointer(..)) |
 582                     err_ub!(InvalidUninitBytes(None)) =>
 583                         { "{}", value } expected { "a function pointer" },
 584                 );
 585                 // FIXME: Check if the signature matches
 586                 Ok(true)
 587             }
 588             ty::Never => throw_validation_failure!(self.path, { "a value of the never type `!`" }),
 589             ty::Foreign(..) | ty::FnDef(..) => {
 590                 // Nothing to check.
 591                 Ok(true)
 592             }
 593             // The above should be all the primitive types. The rest is compound, we
 594             // check them by visiting their fields/variants.
 595             ty::Adt(..)
 596             | ty::Tuple(..)
 597             | ty::Array(..)
 598             | ty::Slice(..)
 599             | ty::Str
 600             | ty::Dynamic(..)
 601             | ty::Closure(..)
 602             | ty::Generator(..) => Ok(false),
 603             // Some types only occur during typechecking, they have no layout.
 604             // We should not see them here and we could not check them anyway.
 605             ty::Error(_)
 606             | ty::Infer(..)
 607             | ty::Placeholder(..)
 608             | ty::Bound(..)
 609             | ty::Param(..)
 610             | ty::Opaque(..)
 611             | ty::Projection(..)
 612             | ty::GeneratorWitness(..) => bug!("Encountered invalid type {:?}", ty),
 613         }
 614     }
 615
 616     fn visit_scalar(
 617         &mut self,
 618         op: &OpTy<'tcx, M::PointerTag>,
 619         scalar_layout: ScalarAbi,
 620     ) -> InterpResult<'tcx> {
 621         if scalar_layout.valid_range.is_full_for(op.layout.size) {
 622             // Nothing to check
 623             return Ok(());
 624         }
 625         // At least one value is excluded.
 626         let valid_range = scalar_layout.valid_range;
 627         let WrappingRange { start, end } = valid_range;
 628         let max_value = op.layout.size.unsigned_int_max();
 629         assert!(end <= max_value);
 630         // Determine the allowed range
 631         let value = self.read_scalar(op)?;
 632         let value = try_validation!(
 633             value.check_init(),
 634             self.path,
 635             err_ub!(InvalidUninitBytes(None)) => { "{}", value }
 636                 expected { "something {}", wrapping_range_format(valid_range, max_value) },
 637         );
 638         let bits = match value.try_to_int() {
 639             Err(_) => {
 640                 // So this is a pointer then, and casting to an int failed.
 641                 // Can only happen during CTFE.
 642                 let ptr = self.ecx.scalar_to_ptr(value);
 643                 if start == 1 && end == max_value {
 644                     // Only null is the niche.  So make sure the ptr is NOT null.
 645                     if self.ecx.memory.ptr_may_be_null(ptr) {
 646                         throw_validation_failure!(self.path,
 647                             { "a potentially null pointer" }
 648                             expected {
 649                                 "something that cannot possibly fail to be {}",
 650                                 wrapping_range_format(valid_range, max_value)
 651                             }
 652                         )
 653                     }
 654                     return Ok(());
 655                 } else {
 656                     // Conservatively, we reject, because the pointer *could* have a bad
 657                     // value.
 658                     throw_validation_failure!(self.path,
 659                         { "a pointer" }
 660                         expected {
 661                             "something that cannot possibly fail to be {}",
 662                             wrapping_range_format(valid_range, max_value)
 663                         }
 664                     )
 665                 }
 666             }
 667             Ok(int) => int.assert_bits(op.layout.size),
 668         };
 669         // Now compare. This is slightly subtle because this is a special "wrap-around" range.
 670         if valid_range.contains(bits) {
 671             Ok(())
 672         } else {
 673             throw_validation_failure!(self.path,
 674                 { "{}", bits }
 675                 expected { "something {}", wrapping_range_format(valid_range, max_value) }
 676             )
 677         }
 678     }
 679 }
 680
 681 impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
 682     for ValidityVisitor<'rt, 'mir, 'tcx, M>
 683 {
 684     type V = OpTy<'tcx, M::PointerTag>;
 685
 686     #[inline(always)]
 687     fn ecx(&self) -> &InterpCx<'mir, 'tcx, M> {
 688         &self.ecx
 689     }
 690
 691     fn read_discriminant(
 692         &mut self,
 693         op: &OpTy<'tcx, M::PointerTag>,
 694     ) -> InterpResult<'tcx, VariantIdx> {
 695         self.with_elem(PathElem::EnumTag, move |this| {
 696             Ok(try_validation!(
 697                 this.ecx.read_discriminant(op),
 698                 this.path,
 699                 err_ub!(InvalidTag(val)) =>
 700                     { "{}", val } expected { "a valid enum tag" },
 701                 err_ub!(InvalidUninitBytes(None)) =>
 702                     { "uninitialized bytes" } expected { "a valid enum tag" },
 703                 err_unsup!(ReadPointerAsBytes) =>
 704                     { "a pointer" } expected { "a valid enum tag" },
 705             )
 706             .1)
 707         })
 708     }
 709
 710     #[inline]
 711     fn visit_field(
 712         &mut self,
 713         old_op: &OpTy<'tcx, M::PointerTag>,
 714         field: usize,
 715         new_op: &OpTy<'tcx, M::PointerTag>,
 716     ) -> InterpResult<'tcx> {
 717         let elem = self.aggregate_field_path_elem(old_op.layout, field);
 718         self.with_elem(elem, move |this| this.visit_value(new_op))
 719     }
 720
 721     #[inline]
 722     fn visit_variant(
 723         &mut self,
 724         old_op: &OpTy<'tcx, M::PointerTag>,
 725         variant_id: VariantIdx,
 726         new_op: &OpTy<'tcx, M::PointerTag>,
 727     ) -> InterpResult<'tcx> {
 728         let name = match old_op.layout.ty.kind() {
 729             ty::Adt(adt, _) => PathElem::Variant(adt.variants[variant_id].name),
 730             // Generators also have variants
 731             ty::Generator(..) => PathElem::GeneratorState(variant_id),
 732             _ => bug!("Unexpected type with variant: {:?}", old_op.layout.ty),
 733         };
 734         self.with_elem(name, move |this| this.visit_value(new_op))
 735     }
 736
 737     #[inline(always)]
 738     fn visit_union(
 739         &mut self,
 740         op: &OpTy<'tcx, M::PointerTag>,
 741         _fields: NonZeroUsize,
 742     ) -> InterpResult<'tcx> {
 743         // Special check preventing `UnsafeCell` inside unions in the inner part of constants.
 744         if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { inner: true, .. })) {
 745             if !op.layout.ty.is_freeze(self.ecx.tcx.at(DUMMY_SP), self.ecx.param_env) {
 746                 throw_validation_failure!(self.path, { "`UnsafeCell` in a `const`" });
 747             }
 748         }
 749         Ok(())
 750     }
 751
 752     #[inline]
 753     fn visit_value(&mut self, op: &OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx> {
 754         trace!("visit_value: {:?}, {:?}", *op, op.layout);
 755
 756         // Check primitive types -- the leafs of our recursive descend.
 757         if self.try_visit_primitive(op)? {
 758             return Ok(());
 759         }
 760         // Sanity check: `builtin_deref` does not know any pointers that are not primitive.
 761         assert!(op.layout.ty.builtin_deref(true).is_none());
 762
 763         // Special check preventing `UnsafeCell` in the inner part of constants
 764         if let Some(def) = op.layout.ty.ty_adt_def() {
 765             if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { inner: true, .. }))
 766                 && Some(def.did) == self.ecx.tcx.lang_items().unsafe_cell_type()
 767             {
 768                 throw_validation_failure!(self.path, { "`UnsafeCell` in a `const`" });
 769             }
 770         }
 771
 772         // Recursively walk the value at its type.
 773         self.walk_value(op)?;
 774
 775         // *After* all of this, check the ABI.  We need to check the ABI to handle
 776         // types like `NonNull` where the `Scalar` info is more restrictive than what
 777         // the fields say (`rustc_layout_scalar_valid_range_start`).
 778         // But in most cases, this will just propagate what the fields say,
 779         // and then we want the error to point at the field -- so, first recurse,
 780         // then check ABI.
 781         //
 782         // FIXME: We could avoid some redundant checks here. For newtypes wrapping
 783         // scalars, we do the same check on every "level" (e.g., first we check
 784         // MyNewtype and then the scalar in there).
 785         match op.layout.abi {
 786             Abi::Uninhabited => {
 787                 throw_validation_failure!(self.path,
 788                     { "a value of uninhabited type {:?}", op.layout.ty }
 789                 );
 790             }
 791             Abi::Scalar(scalar_layout) => {
 792                 self.visit_scalar(op, scalar_layout)?;
 793             }
 794             Abi::ScalarPair { .. } | Abi::Vector { .. } => {
 795                 // These have fields that we already visited above, so we already checked
 796                 // all their scalar-level restrictions.
 797                 // There is also no equivalent to `rustc_layout_scalar_valid_range_start`
 798                 // that would make skipping them here an issue.
 799             }
 800             Abi::Aggregate { .. } => {
 801                 // Nothing to do.
 802             }
 803         }
 804
 805         Ok(())
 806     }
 807
 808     fn visit_aggregate(
 809         &mut self,
 810         op: &OpTy<'tcx, M::PointerTag>,
 811         fields: impl Iterator<Item = InterpResult<'tcx, Self::V>>,
 812     ) -> InterpResult<'tcx> {
 813         match op.layout.ty.kind() {
 814             ty::Str => {
 815                 let mplace = op.assert_mem_place(); // strings are never immediate
 816                 let len = mplace.len(self.ecx)?;
 817                 try_validation!(
 818                     self.ecx.memory.read_bytes(mplace.ptr, Size::from_bytes(len)),
 819                     self.path,
 820                     err_ub!(InvalidUninitBytes(..)) => { "uninitialized data in `str`" },
 821                     err_unsup!(ReadPointerAsBytes) => { "a pointer in `str`" },
 822                 );
 823             }
 824             ty::Array(tys, ..) | ty::Slice(tys)
 825                 // This optimization applies for types that can hold arbitrary bytes (such as
 826                 // integer and floating point types) or for structs or tuples with no fields.
 827                 // FIXME(wesleywiser) This logic could be extended further to arbitrary structs
 828                 // or tuples made up of integer/floating point types or inhabited ZSTs with no
 829                 // padding.
 830                 if matches!(tys.kind(), ty::Int(..) | ty::Uint(..) | ty::Float(..))
 831                 =>
 832             {
 833                 // Optimized handling for arrays of integer/float type.
 834
 835                 // Arrays cannot be immediate, slices are never immediate.
 836                 let mplace = op.assert_mem_place();
 837                 // This is the length of the array/slice.
 838                 let len = mplace.len(self.ecx)?;
 839                 // This is the element type size.
 840                 let layout = self.ecx.layout_of(*tys)?;
 841                 // This is the size in bytes of the whole array. (This checks for overflow.)
 842                 let size = layout.size * len;
 843
 844                 // Optimization: we just check the entire range at once.
 845                 // NOTE: Keep this in sync with the handling of integer and float
 846                 // types above, in `visit_primitive`.
 847                 // In run-time mode, we accept pointers in here.  This is actually more
 848                 // permissive than a per-element check would be, e.g., we accept
 849                 // a &[u8] that contains a pointer even though bytewise checking would
 850                 // reject it.  However, that's good: We don't inherently want
 851                 // to reject those pointers, we just do not have the machinery to
 852                 // talk about parts of a pointer.
 853                 // We also accept uninit, for consistency with the slow path.
 854                 let alloc = match self.ecx.memory.get(mplace.ptr, size, mplace.align)? {
 855                     Some(a) => a,
 856                     None => {
 857                         // Size 0, nothing more to check.
 858                         return Ok(());
 859                     }
 860                 };
 861
 862                 let allow_uninit_and_ptr = !M::enforce_number_validity(self.ecx);
 863                 match alloc.check_bytes(
 864                     alloc_range(Size::ZERO, size),
 865                     allow_uninit_and_ptr,
 866                 ) {
 867                     // In the happy case, we needn't check anything else.
 868                     Ok(()) => {}
 869                     // Some error happened, try to provide a more detailed description.
 870                     Err(err) => {
 871                         // For some errors we might be able to provide extra information.
 872                         // (This custom logic does not fit the `try_validation!` macro.)
 873                         match err.kind() {
 874                             err_ub!(InvalidUninitBytes(Some((_alloc_id, access)))) => {
 875                                 // Some byte was uninitialized, determine which
 876                                 // element that byte belongs to so we can
 877                                 // provide an index.
 878                                 let i = usize::try_from(
 879                                     access.uninit_offset.bytes() / layout.size.bytes(),
 880                                 )
 881                                 .unwrap();
 882                                 self.path.push(PathElem::ArrayElem(i));
 883
 884                                 throw_validation_failure!(self.path, { "uninitialized bytes" })
 885                             }
 886                             err_unsup!(ReadPointerAsBytes) => {
 887                                 throw_validation_failure!(self.path, { "a pointer" } expected { "plain (non-pointer) bytes" })
 888                             }
 889
 890                             // Propagate upwards (that will also check for unexpected errors).
 891                             _ => return Err(err),
 892                         }
 893                     }
 894                 }
 895             }
 896             // Fast path for arrays and slices of ZSTs. We only need to check a single ZST element
 897             // of an array and not all of them, because there's only a single value of a specific
 898             // ZST type, so either validation fails for all elements or none.
 899             ty::Array(tys, ..) | ty::Slice(tys) if self.ecx.layout_of(*tys)?.is_zst() => {
 900                 // Validate just the first element (if any).
 901                 self.walk_aggregate(op, fields.take(1))?
 902             }
 903             _ => {
 904                 self.walk_aggregate(op, fields)? // default handler
 905             }
 906         }
 907         Ok(())
 908     }
 909 }
 910
 911 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 912     fn validate_operand_internal(
 913         &self,
 914         op: &OpTy<'tcx, M::PointerTag>,
 915         path: Vec<PathElem>,
 916         ref_tracking: Option<&mut RefTracking<MPlaceTy<'tcx, M::PointerTag>, Vec<PathElem>>>,
 917         ctfe_mode: Option<CtfeValidationMode>,
 918     ) -> InterpResult<'tcx> {
 919         trace!("validate_operand_internal: {:?}, {:?}", *op, op.layout.ty);
 920
 921         // Construct a visitor
 922         let mut visitor = ValidityVisitor { path, ref_tracking, ctfe_mode, ecx: self };
 923
 924         // Run it.
 925         match visitor.visit_value(&op) {
 926             Ok(()) => Ok(()),
 927             // Pass through validation failures.
 928             Err(err) if matches!(err.kind(), err_ub!(ValidationFailure { .. })) => Err(err),
 929             // Also pass through InvalidProgram, those just indicate that we could not
 930             // validate and each caller will know best what to do with them.
 931             Err(err) if matches!(err.kind(), InterpError::InvalidProgram(_)) => Err(err),
 932             // Avoid other errors as those do not show *where* in the value the issue lies.
 933             Err(err) => {
 934                 err.print_backtrace();
 935                 bug!("Unexpected error during validation: {}", err);
 936             }
 937         }
 938     }
 939
 940     /// This function checks the data at `op` to be const-valid.
 941     /// `op` is assumed to cover valid memory if it is an indirect operand.
 942     /// It will error if the bits at the destination do not match the ones described by the layout.
 943     ///
 944     /// `ref_tracking` is used to record references that we encounter so that they
 945     /// can be checked recursively by an outside driving loop.
 946     ///
 947     /// `constant` controls whether this must satisfy the rules for constants:
 948     /// - no pointers to statics.
 949     /// - no `UnsafeCell` or non-ZST `&mut`.
 950     #[inline(always)]
 951     pub fn const_validate_operand(
 952         &self,
 953         op: &OpTy<'tcx, M::PointerTag>,
 954         path: Vec<PathElem>,
 955         ref_tracking: &mut RefTracking<MPlaceTy<'tcx, M::PointerTag>, Vec<PathElem>>,
 956         ctfe_mode: CtfeValidationMode,
 957     ) -> InterpResult<'tcx> {
 958         self.validate_operand_internal(op, path, Some(ref_tracking), Some(ctfe_mode))
 959     }
 960
 961     /// This function checks the data at `op` to be runtime-valid.
 962     /// `op` is assumed to cover valid memory if it is an indirect operand.
 963     /// It will error if the bits at the destination do not match the ones described by the layout.
 964     #[inline(always)]
 965     pub fn validate_operand(&self, op: &OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx> {
 966         self.validate_operand_internal(op, vec![], None, None)
 967     }
 968 }