arch/x86/include/asm/mmu_context.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_X86_MMU_CONTEXT_H
   3 #define _ASM_X86_MMU_CONTEXT_H
   4
   5 #include <asm/desc.h>
   6 #include <linux/atomic.h>
   7 #include <linux/mm_types.h>
   8 #include <linux/pkeys.h>
   9
  10 #include <trace/events/tlb.h>
  11
  12 #include <asm/pgalloc.h>
  13 #include <asm/tlbflush.h>
  14 #include <asm/paravirt.h>
  15 #include <asm/mpx.h>
  16
  17 extern atomic64_t last_mm_ctx_id;
  18
  19 #ifndef CONFIG_PARAVIRT
  20 static inline void paravirt_activate_mm(struct mm_struct *prev,
  21                                         struct mm_struct *next)
  22 {
  23 }
  24 #endif  /* !CONFIG_PARAVIRT */
  25
  26 #ifdef CONFIG_PERF_EVENTS
  27 extern struct static_key rdpmc_always_available;
  28
  29 static inline void load_mm_cr4(struct mm_struct *mm)
  30 {
  31         if (static_key_false(&rdpmc_always_available) ||
  32             atomic_read(&mm->context.perf_rdpmc_allowed))
  33                 cr4_set_bits(X86_CR4_PCE);
  34         else
  35                 cr4_clear_bits(X86_CR4_PCE);
  36 }
  37 #else
  38 static inline void load_mm_cr4(struct mm_struct *mm) {}
  39 #endif
  40
  41 #ifdef CONFIG_MODIFY_LDT_SYSCALL
  42 /*
  43  * ldt_structs can be allocated, used, and freed, but they are never
  44  * modified while live.
  45  */
  46 struct ldt_struct {
  47         /*
  48          * Xen requires page-aligned LDTs with special permissions.  This is
  49          * needed to prevent us from installing evil descriptors such as
  50          * call gates.  On native, we could merge the ldt_struct and LDT
  51          * allocations, but it's not worth trying to optimize.
  52          */
  53         struct desc_struct      *entries;
  54         unsigned int            nr_entries;
  55
  56         /*
  57          * If PTI is in use, then the entries array is not mapped while we're
  58          * in user mode.  The whole array will be aliased at the addressed
  59          * given by ldt_slot_va(slot).  We use two slots so that we can allocate
  60          * and map, and enable a new LDT without invalidating the mapping
  61          * of an older, still-in-use LDT.
  62          *
  63          * slot will be -1 if this LDT doesn't have an alias mapping.
  64          */
  65         int                     slot;
  66 };
  67
  68 /* This is a multiple of PAGE_SIZE. */
  69 #define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
  70
  71 static inline void *ldt_slot_va(int slot)
  72 {
  73 #ifdef CONFIG_X86_64
  74         return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
  75 #else
  76         BUG();
  77 #endif
  78 }
  79
  80 /*
  81  * Used for LDT copy/destruction.
  82  */
  83 static inline void init_new_context_ldt(struct mm_struct *mm)
  84 {
  85         mm->context.ldt = NULL;
  86         init_rwsem(&mm->context.ldt_usr_sem);
  87 }
  88 int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm);
  89 void destroy_context_ldt(struct mm_struct *mm);
  90 void ldt_arch_exit_mmap(struct mm_struct *mm);
  91 #else   /* CONFIG_MODIFY_LDT_SYSCALL */
  92 static inline void init_new_context_ldt(struct mm_struct *mm) { }
  93 static inline int ldt_dup_context(struct mm_struct *oldmm,
  94                                   struct mm_struct *mm)
  95 {
  96         return 0;
  97 }
  98 static inline void destroy_context_ldt(struct mm_struct *mm) { }
  99 static inline void ldt_arch_exit_mmap(struct mm_struct *mm) { }
 100 #endif
 101
 102 static inline void load_mm_ldt(struct mm_struct *mm)
 103 {
 104 #ifdef CONFIG_MODIFY_LDT_SYSCALL
 105         struct ldt_struct *ldt;
 106
 107         /* READ_ONCE synchronizes with smp_store_release */
 108         ldt = READ_ONCE(mm->context.ldt);
 109
 110         /*
 111          * Any change to mm->context.ldt is followed by an IPI to all
 112          * CPUs with the mm active.  The LDT will not be freed until
 113          * after the IPI is handled by all such CPUs.  This means that,
 114          * if the ldt_struct changes before we return, the values we see
 115          * will be safe, and the new values will be loaded before we run
 116          * any user code.
 117          *
 118          * NB: don't try to convert this to use RCU without extreme care.
 119          * We would still need IRQs off, because we don't want to change
 120          * the local LDT after an IPI loaded a newer value than the one
 121          * that we can see.
 122          */
 123
 124         if (unlikely(ldt)) {
 125                 if (static_cpu_has(X86_FEATURE_PTI)) {
 126                         if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) {
 127                                 /*
 128                                  * Whoops -- either the new LDT isn't mapped
 129                                  * (if slot == -1) or is mapped into a bogus
 130                                  * slot (if slot > 1).
 131                                  */
 132                                 clear_LDT();
 133                                 return;
 134                         }
 135
 136                         /*
 137                          * If page table isolation is enabled, ldt->entries
 138                          * will not be mapped in the userspace pagetables.
 139                          * Tell the CPU to access the LDT through the alias
 140                          * at ldt_slot_va(ldt->slot).
 141                          */
 142                         set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries);
 143                 } else {
 144                         set_ldt(ldt->entries, ldt->nr_entries);
 145                 }
 146         } else {
 147                 clear_LDT();
 148         }
 149 #else
 150         clear_LDT();
 151 #endif
 152 }
 153
 154 static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
 155 {
 156 #ifdef CONFIG_MODIFY_LDT_SYSCALL
 157         /*
 158          * Load the LDT if either the old or new mm had an LDT.
 159          *
 160          * An mm will never go from having an LDT to not having an LDT.  Two
 161          * mms never share an LDT, so we don't gain anything by checking to
 162          * see whether the LDT changed.  There's also no guarantee that
 163          * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
 164          * then prev->context.ldt will also be non-NULL.
 165          *
 166          * If we really cared, we could optimize the case where prev == next
 167          * and we're exiting lazy mode.  Most of the time, if this happens,
 168          * we don't actually need to reload LDTR, but modify_ldt() is mostly
 169          * used by legacy code and emulators where we don't need this level of
 170          * performance.
 171          *
 172          * This uses | instead of || because it generates better code.
 173          */
 174         if (unlikely((unsigned long)prev->context.ldt |
 175                      (unsigned long)next->context.ldt))
 176                 load_mm_ldt(next);
 177 #endif
 178
 179         DEBUG_LOCKS_WARN_ON(preemptible());
 180 }
 181
 182 void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
 183
 184 static inline int init_new_context(struct task_struct *tsk,
 185                                    struct mm_struct *mm)
 186 {
 187         mutex_init(&mm->context.lock);
 188
 189         mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id);
 190         atomic64_set(&mm->context.tlb_gen, 0);
 191
 192 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 193         if (cpu_feature_enabled(X86_FEATURE_OSPKE)) {
 194                 /* pkey 0 is the default and always allocated */
 195                 mm->context.pkey_allocation_map = 0x1;
 196                 /* -1 means unallocated or invalid */
 197                 mm->context.execute_only_pkey = -1;
 198         }
 199 #endif
 200         init_new_context_ldt(mm);
 201         return 0;
 202 }
 203 static inline void destroy_context(struct mm_struct *mm)
 204 {
 205         destroy_context_ldt(mm);
 206 }
 207
 208 extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 209                       struct task_struct *tsk);
 210
 211 extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 212                                struct task_struct *tsk);
 213 #define switch_mm_irqs_off switch_mm_irqs_off
 214
 215 #define activate_mm(prev, next)                 \
 216 do {                                            \
 217         paravirt_activate_mm((prev), (next));   \
 218         switch_mm((prev), (next), NULL);        \
 219 } while (0);
 220
 221 #ifdef CONFIG_X86_32
 222 #define deactivate_mm(tsk, mm)                  \
 223 do {                                            \
 224         lazy_load_gs(0);                        \
 225 } while (0)
 226 #else
 227 #define deactivate_mm(tsk, mm)                  \
 228 do {                                            \
 229         load_gs_index(0);                       \
 230         loadsegment(fs, 0);                     \
 231 } while (0)
 232 #endif
 233
 234 static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
 235 {
 236         paravirt_arch_dup_mmap(oldmm, mm);
 237         return ldt_dup_context(oldmm, mm);
 238 }
 239
 240 static inline void arch_exit_mmap(struct mm_struct *mm)
 241 {
 242         paravirt_arch_exit_mmap(mm);
 243         ldt_arch_exit_mmap(mm);
 244 }
 245
 246 #ifdef CONFIG_X86_64
 247 static inline bool is_64bit_mm(struct mm_struct *mm)
 248 {
 249         return  !IS_ENABLED(CONFIG_IA32_EMULATION) ||
 250                 !(mm->context.ia32_compat == TIF_IA32);
 251 }
 252 #else
 253 static inline bool is_64bit_mm(struct mm_struct *mm)
 254 {
 255         return false;
 256 }
 257 #endif
 258
 259 static inline void arch_bprm_mm_init(struct mm_struct *mm,
 260                 struct vm_area_struct *vma)
 261 {
 262         mpx_mm_init(mm);
 263 }
 264
 265 static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 266                               unsigned long start, unsigned long end)
 267 {
 268         /*
 269          * mpx_notify_unmap() goes and reads a rarely-hot
 270          * cacheline in the mm_struct.  That can be expensive
 271          * enough to be seen in profiles.
 272          *
 273          * The mpx_notify_unmap() call and its contents have been
 274          * observed to affect munmap() performance on hardware
 275          * where MPX is not present.
 276          *
 277          * The unlikely() optimizes for the fast case: no MPX
 278          * in the CPU, or no MPX use in the process.  Even if
 279          * we get this wrong (in the unlikely event that MPX
 280          * is widely enabled on some system) the overhead of
 281          * MPX itself (reading bounds tables) is expected to
 282          * overwhelm the overhead of getting this unlikely()
 283          * consistently wrong.
 284          */
 285         if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX)))
 286                 mpx_notify_unmap(mm, vma, start, end);
 287 }
 288
 289 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 290 static inline int vma_pkey(struct vm_area_struct *vma)
 291 {
 292         unsigned long vma_pkey_mask = VM_PKEY_BIT0 | VM_PKEY_BIT1 |
 293                                       VM_PKEY_BIT2 | VM_PKEY_BIT3;
 294
 295         return (vma->vm_flags & vma_pkey_mask) >> VM_PKEY_SHIFT;
 296 }
 297 #else
 298 static inline int vma_pkey(struct vm_area_struct *vma)
 299 {
 300         return 0;
 301 }
 302 #endif
 303
 304 /*
 305  * We only want to enforce protection keys on the current process
 306  * because we effectively have no access to PKRU for other
 307  * processes or any way to tell *which * PKRU in a threaded
 308  * process we could use.
 309  *
 310  * So do not enforce things if the VMA is not from the current
 311  * mm, or if we are in a kernel thread.
 312  */
 313 static inline bool vma_is_foreign(struct vm_area_struct *vma)
 314 {
 315         if (!current->mm)
 316                 return true;
 317         /*
 318          * Should PKRU be enforced on the access to this VMA?  If
 319          * the VMA is from another process, then PKRU has no
 320          * relevance and should not be enforced.
 321          */
 322         if (current->mm != vma->vm_mm)
 323                 return true;
 324
 325         return false;
 326 }
 327
 328 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 329                 bool write, bool execute, bool foreign)
 330 {
 331         /* pkeys never affect instruction fetches */
 332         if (execute)
 333                 return true;
 334         /* allow access if the VMA is not one from this process */
 335         if (foreign || vma_is_foreign(vma))
 336                 return true;
 337         return __pkru_allows_pkey(vma_pkey(vma), write);
 338 }
 339
 340 /*
 341  * This can be used from process context to figure out what the value of
 342  * CR3 is without needing to do a (slow) __read_cr3().
 343  *
 344  * It's intended to be used for code like KVM that sneakily changes CR3
 345  * and needs to restore it.  It needs to be used very carefully.
 346  */
 347 static inline unsigned long __get_current_cr3_fast(void)
 348 {
 349         unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
 350                 this_cpu_read(cpu_tlbstate.loaded_mm_asid));
 351
 352         /* For now, be very restrictive about when this can be called. */
 353         VM_WARN_ON(in_nmi() || preemptible());
 354
 355         VM_BUG_ON(cr3 != __read_cr3());
 356         return cr3;
 357 }
 358
 359 #endif /* _ASM_X86_MMU_CONTEXT_H */