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 /*
  58  * Used for LDT copy/destruction.
  59  */
  60 static inline void init_new_context_ldt(struct mm_struct *mm)
  61 {
  62         mm->context.ldt = NULL;
  63         init_rwsem(&mm->context.ldt_usr_sem);
  64 }
  65 int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm);
  66 void destroy_context_ldt(struct mm_struct *mm);
  67 #else   /* CONFIG_MODIFY_LDT_SYSCALL */
  68 static inline void init_new_context_ldt(struct mm_struct *mm) { }
  69 static inline int ldt_dup_context(struct mm_struct *oldmm,
  70                                   struct mm_struct *mm)
  71 {
  72         return 0;
  73 }
  74 static inline void destroy_context_ldt(struct mm_struct *mm) {}
  75 #endif
  76
  77 static inline void load_mm_ldt(struct mm_struct *mm)
  78 {
  79 #ifdef CONFIG_MODIFY_LDT_SYSCALL
  80         struct ldt_struct *ldt;
  81
  82         /* READ_ONCE synchronizes with smp_store_release */
  83         ldt = READ_ONCE(mm->context.ldt);
  84
  85         /*
  86          * Any change to mm->context.ldt is followed by an IPI to all
  87          * CPUs with the mm active.  The LDT will not be freed until
  88          * after the IPI is handled by all such CPUs.  This means that,
  89          * if the ldt_struct changes before we return, the values we see
  90          * will be safe, and the new values will be loaded before we run
  91          * any user code.
  92          *
  93          * NB: don't try to convert this to use RCU without extreme care.
  94          * We would still need IRQs off, because we don't want to change
  95          * the local LDT after an IPI loaded a newer value than the one
  96          * that we can see.
  97          */
  98
  99         if (unlikely(ldt))
 100                 set_ldt(ldt->entries, ldt->nr_entries);
 101         else
 102                 clear_LDT();
 103 #else
 104         clear_LDT();
 105 #endif
 106 }
 107
 108 static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
 109 {
 110 #ifdef CONFIG_MODIFY_LDT_SYSCALL
 111         /*
 112          * Load the LDT if either the old or new mm had an LDT.
 113          *
 114          * An mm will never go from having an LDT to not having an LDT.  Two
 115          * mms never share an LDT, so we don't gain anything by checking to
 116          * see whether the LDT changed.  There's also no guarantee that
 117          * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
 118          * then prev->context.ldt will also be non-NULL.
 119          *
 120          * If we really cared, we could optimize the case where prev == next
 121          * and we're exiting lazy mode.  Most of the time, if this happens,
 122          * we don't actually need to reload LDTR, but modify_ldt() is mostly
 123          * used by legacy code and emulators where we don't need this level of
 124          * performance.
 125          *
 126          * This uses | instead of || because it generates better code.
 127          */
 128         if (unlikely((unsigned long)prev->context.ldt |
 129                      (unsigned long)next->context.ldt))
 130                 load_mm_ldt(next);
 131 #endif
 132
 133         DEBUG_LOCKS_WARN_ON(preemptible());
 134 }
 135
 136 void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
 137
 138 static inline int init_new_context(struct task_struct *tsk,
 139                                    struct mm_struct *mm)
 140 {
 141         mutex_init(&mm->context.lock);
 142
 143         mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id);
 144         atomic64_set(&mm->context.tlb_gen, 0);
 145
 146 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 147         if (cpu_feature_enabled(X86_FEATURE_OSPKE)) {
 148                 /* pkey 0 is the default and always allocated */
 149                 mm->context.pkey_allocation_map = 0x1;
 150                 /* -1 means unallocated or invalid */
 151                 mm->context.execute_only_pkey = -1;
 152         }
 153 #endif
 154         init_new_context_ldt(mm);
 155         return 0;
 156 }
 157 static inline void destroy_context(struct mm_struct *mm)
 158 {
 159         destroy_context_ldt(mm);
 160 }
 161
 162 extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 163                       struct task_struct *tsk);
 164
 165 extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 166                                struct task_struct *tsk);
 167 #define switch_mm_irqs_off switch_mm_irqs_off
 168
 169 #define activate_mm(prev, next)                 \
 170 do {                                            \
 171         paravirt_activate_mm((prev), (next));   \
 172         switch_mm((prev), (next), NULL);        \
 173 } while (0);
 174
 175 #ifdef CONFIG_X86_32
 176 #define deactivate_mm(tsk, mm)                  \
 177 do {                                            \
 178         lazy_load_gs(0);                        \
 179 } while (0)
 180 #else
 181 #define deactivate_mm(tsk, mm)                  \
 182 do {                                            \
 183         load_gs_index(0);                       \
 184         loadsegment(fs, 0);                     \
 185 } while (0)
 186 #endif
 187
 188 static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
 189 {
 190         paravirt_arch_dup_mmap(oldmm, mm);
 191         return ldt_dup_context(oldmm, mm);
 192 }
 193
 194 static inline void arch_exit_mmap(struct mm_struct *mm)
 195 {
 196         paravirt_arch_exit_mmap(mm);
 197 }
 198
 199 #ifdef CONFIG_X86_64
 200 static inline bool is_64bit_mm(struct mm_struct *mm)
 201 {
 202         return  !IS_ENABLED(CONFIG_IA32_EMULATION) ||
 203                 !(mm->context.ia32_compat == TIF_IA32);
 204 }
 205 #else
 206 static inline bool is_64bit_mm(struct mm_struct *mm)
 207 {
 208         return false;
 209 }
 210 #endif
 211
 212 static inline void arch_bprm_mm_init(struct mm_struct *mm,
 213                 struct vm_area_struct *vma)
 214 {
 215         mpx_mm_init(mm);
 216 }
 217
 218 static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 219                               unsigned long start, unsigned long end)
 220 {
 221         /*
 222          * mpx_notify_unmap() goes and reads a rarely-hot
 223          * cacheline in the mm_struct.  That can be expensive
 224          * enough to be seen in profiles.
 225          *
 226          * The mpx_notify_unmap() call and its contents have been
 227          * observed to affect munmap() performance on hardware
 228          * where MPX is not present.
 229          *
 230          * The unlikely() optimizes for the fast case: no MPX
 231          * in the CPU, or no MPX use in the process.  Even if
 232          * we get this wrong (in the unlikely event that MPX
 233          * is widely enabled on some system) the overhead of
 234          * MPX itself (reading bounds tables) is expected to
 235          * overwhelm the overhead of getting this unlikely()
 236          * consistently wrong.
 237          */
 238         if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX)))
 239                 mpx_notify_unmap(mm, vma, start, end);
 240 }
 241
 242 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 243 static inline int vma_pkey(struct vm_area_struct *vma)
 244 {
 245         unsigned long vma_pkey_mask = VM_PKEY_BIT0 | VM_PKEY_BIT1 |
 246                                       VM_PKEY_BIT2 | VM_PKEY_BIT3;
 247
 248         return (vma->vm_flags & vma_pkey_mask) >> VM_PKEY_SHIFT;
 249 }
 250 #else
 251 static inline int vma_pkey(struct vm_area_struct *vma)
 252 {
 253         return 0;
 254 }
 255 #endif
 256
 257 /*
 258  * We only want to enforce protection keys on the current process
 259  * because we effectively have no access to PKRU for other
 260  * processes or any way to tell *which * PKRU in a threaded
 261  * process we could use.
 262  *
 263  * So do not enforce things if the VMA is not from the current
 264  * mm, or if we are in a kernel thread.
 265  */
 266 static inline bool vma_is_foreign(struct vm_area_struct *vma)
 267 {
 268         if (!current->mm)
 269                 return true;
 270         /*
 271          * Should PKRU be enforced on the access to this VMA?  If
 272          * the VMA is from another process, then PKRU has no
 273          * relevance and should not be enforced.
 274          */
 275         if (current->mm != vma->vm_mm)
 276                 return true;
 277
 278         return false;
 279 }
 280
 281 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 282                 bool write, bool execute, bool foreign)
 283 {
 284         /* pkeys never affect instruction fetches */
 285         if (execute)
 286                 return true;
 287         /* allow access if the VMA is not one from this process */
 288         if (foreign || vma_is_foreign(vma))
 289                 return true;
 290         return __pkru_allows_pkey(vma_pkey(vma), write);
 291 }
 292
 293 /*
 294  * This can be used from process context to figure out what the value of
 295  * CR3 is without needing to do a (slow) __read_cr3().
 296  *
 297  * It's intended to be used for code like KVM that sneakily changes CR3
 298  * and needs to restore it.  It needs to be used very carefully.
 299  */
 300 static inline unsigned long __get_current_cr3_fast(void)
 301 {
 302         unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
 303                 this_cpu_read(cpu_tlbstate.loaded_mm_asid));
 304
 305         /* For now, be very restrictive about when this can be called. */
 306         VM_WARN_ON(in_nmi() || preemptible());
 307
 308         VM_BUG_ON(cr3 != __read_cr3());
 309         return cr3;
 310 }
 311
 312 #endif /* _ASM_X86_MMU_CONTEXT_H */