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
  28 DECLARE_STATIC_KEY_FALSE(rdpmc_always_available_key);
  29
  30 static inline void load_mm_cr4(struct mm_struct *mm)
  31 {
  32         if (static_branch_unlikely(&rdpmc_always_available_key) ||
  33             atomic_read(&mm->context.perf_rdpmc_allowed))
  34                 cr4_set_bits(X86_CR4_PCE);
  35         else
  36                 cr4_clear_bits(X86_CR4_PCE);
  37 }
  38 #else
  39 static inline void load_mm_cr4(struct mm_struct *mm) {}
  40 #endif
  41
  42 #ifdef CONFIG_MODIFY_LDT_SYSCALL
  43 /*
  44  * ldt_structs can be allocated, used, and freed, but they are never
  45  * modified while live.
  46  */
  47 struct ldt_struct {
  48         /*
  49          * Xen requires page-aligned LDTs with special permissions.  This is
  50          * needed to prevent us from installing evil descriptors such as
  51          * call gates.  On native, we could merge the ldt_struct and LDT
  52          * allocations, but it's not worth trying to optimize.
  53          */
  54         struct desc_struct      *entries;
  55         unsigned int            nr_entries;
  56
  57         /*
  58          * If PTI is in use, then the entries array is not mapped while we're
  59          * in user mode.  The whole array will be aliased at the addressed
  60          * given by ldt_slot_va(slot).  We use two slots so that we can allocate
  61          * and map, and enable a new LDT without invalidating the mapping
  62          * of an older, still-in-use LDT.
  63          *
  64          * slot will be -1 if this LDT doesn't have an alias mapping.
  65          */
  66         int                     slot;
  67 };
  68
  69 /* This is a multiple of PAGE_SIZE. */
  70 #define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
  71
  72 static inline void *ldt_slot_va(int slot)
  73 {
  74         return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
  75 }
  76
  77 /*
  78  * Used for LDT copy/destruction.
  79  */
  80 static inline void init_new_context_ldt(struct mm_struct *mm)
  81 {
  82         mm->context.ldt = NULL;
  83         init_rwsem(&mm->context.ldt_usr_sem);
  84 }
  85 int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm);
  86 void destroy_context_ldt(struct mm_struct *mm);
  87 void ldt_arch_exit_mmap(struct mm_struct *mm);
  88 #else   /* CONFIG_MODIFY_LDT_SYSCALL */
  89 static inline void init_new_context_ldt(struct mm_struct *mm) { }
  90 static inline int ldt_dup_context(struct mm_struct *oldmm,
  91                                   struct mm_struct *mm)
  92 {
  93         return 0;
  94 }
  95 static inline void destroy_context_ldt(struct mm_struct *mm) { }
  96 static inline void ldt_arch_exit_mmap(struct mm_struct *mm) { }
  97 #endif
  98
  99 static inline void load_mm_ldt(struct mm_struct *mm)
 100 {
 101 #ifdef CONFIG_MODIFY_LDT_SYSCALL
 102         struct ldt_struct *ldt;
 103
 104         /* READ_ONCE synchronizes with smp_store_release */
 105         ldt = READ_ONCE(mm->context.ldt);
 106
 107         /*
 108          * Any change to mm->context.ldt is followed by an IPI to all
 109          * CPUs with the mm active.  The LDT will not be freed until
 110          * after the IPI is handled by all such CPUs.  This means that,
 111          * if the ldt_struct changes before we return, the values we see
 112          * will be safe, and the new values will be loaded before we run
 113          * any user code.
 114          *
 115          * NB: don't try to convert this to use RCU without extreme care.
 116          * We would still need IRQs off, because we don't want to change
 117          * the local LDT after an IPI loaded a newer value than the one
 118          * that we can see.
 119          */
 120
 121         if (unlikely(ldt)) {
 122                 if (static_cpu_has(X86_FEATURE_PTI)) {
 123                         if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) {
 124                                 /*
 125                                  * Whoops -- either the new LDT isn't mapped
 126                                  * (if slot == -1) or is mapped into a bogus
 127                                  * slot (if slot > 1).
 128                                  */
 129                                 clear_LDT();
 130                                 return;
 131                         }
 132
 133                         /*
 134                          * If page table isolation is enabled, ldt->entries
 135                          * will not be mapped in the userspace pagetables.
 136                          * Tell the CPU to access the LDT through the alias
 137                          * at ldt_slot_va(ldt->slot).
 138                          */
 139                         set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries);
 140                 } else {
 141                         set_ldt(ldt->entries, ldt->nr_entries);
 142                 }
 143         } else {
 144                 clear_LDT();
 145         }
 146 #else
 147         clear_LDT();
 148 #endif
 149 }
 150
 151 static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
 152 {
 153 #ifdef CONFIG_MODIFY_LDT_SYSCALL
 154         /*
 155          * Load the LDT if either the old or new mm had an LDT.
 156          *
 157          * An mm will never go from having an LDT to not having an LDT.  Two
 158          * mms never share an LDT, so we don't gain anything by checking to
 159          * see whether the LDT changed.  There's also no guarantee that
 160          * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
 161          * then prev->context.ldt will also be non-NULL.
 162          *
 163          * If we really cared, we could optimize the case where prev == next
 164          * and we're exiting lazy mode.  Most of the time, if this happens,
 165          * we don't actually need to reload LDTR, but modify_ldt() is mostly
 166          * used by legacy code and emulators where we don't need this level of
 167          * performance.
 168          *
 169          * This uses | instead of || because it generates better code.
 170          */
 171         if (unlikely((unsigned long)prev->context.ldt |
 172                      (unsigned long)next->context.ldt))
 173                 load_mm_ldt(next);
 174 #endif
 175
 176         DEBUG_LOCKS_WARN_ON(preemptible());
 177 }
 178
 179 void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
 180
 181 /*
 182  * Init a new mm.  Used on mm copies, like at fork()
 183  * and on mm's that are brand-new, like at execve().
 184  */
 185 static inline int init_new_context(struct task_struct *tsk,
 186                                    struct mm_struct *mm)
 187 {
 188         mutex_init(&mm->context.lock);
 189
 190         mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id);
 191         atomic64_set(&mm->context.tlb_gen, 0);
 192
 193 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 194         if (cpu_feature_enabled(X86_FEATURE_OSPKE)) {
 195                 /* pkey 0 is the default and allocated implicitly */
 196                 mm->context.pkey_allocation_map = 0x1;
 197                 /* -1 means unallocated or invalid */
 198                 mm->context.execute_only_pkey = -1;
 199         }
 200 #endif
 201         init_new_context_ldt(mm);
 202         return 0;
 203 }
 204 static inline void destroy_context(struct mm_struct *mm)
 205 {
 206         destroy_context_ldt(mm);
 207 }
 208
 209 extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 210                       struct task_struct *tsk);
 211
 212 extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 213                                struct task_struct *tsk);
 214 #define switch_mm_irqs_off switch_mm_irqs_off
 215
 216 #define activate_mm(prev, next)                 \
 217 do {                                            \
 218         paravirt_activate_mm((prev), (next));   \
 219         switch_mm((prev), (next), NULL);        \
 220 } while (0);
 221
 222 #ifdef CONFIG_X86_32
 223 #define deactivate_mm(tsk, mm)                  \
 224 do {                                            \
 225         lazy_load_gs(0);                        \
 226 } while (0)
 227 #else
 228 #define deactivate_mm(tsk, mm)                  \
 229 do {                                            \
 230         load_gs_index(0);                       \
 231         loadsegment(fs, 0);                     \
 232 } while (0)
 233 #endif
 234
 235 static inline void arch_dup_pkeys(struct mm_struct *oldmm,
 236                                   struct mm_struct *mm)
 237 {
 238 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 239         if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
 240                 return;
 241
 242         /* Duplicate the oldmm pkey state in mm: */
 243         mm->context.pkey_allocation_map = oldmm->context.pkey_allocation_map;
 244         mm->context.execute_only_pkey   = oldmm->context.execute_only_pkey;
 245 #endif
 246 }
 247
 248 static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
 249 {
 250         arch_dup_pkeys(oldmm, mm);
 251         paravirt_arch_dup_mmap(oldmm, mm);
 252         return ldt_dup_context(oldmm, mm);
 253 }
 254
 255 static inline void arch_exit_mmap(struct mm_struct *mm)
 256 {
 257         paravirt_arch_exit_mmap(mm);
 258         ldt_arch_exit_mmap(mm);
 259 }
 260
 261 #ifdef CONFIG_X86_64
 262 static inline bool is_64bit_mm(struct mm_struct *mm)
 263 {
 264         return  !IS_ENABLED(CONFIG_IA32_EMULATION) ||
 265                 !(mm->context.ia32_compat == TIF_IA32);
 266 }
 267 #else
 268 static inline bool is_64bit_mm(struct mm_struct *mm)
 269 {
 270         return false;
 271 }
 272 #endif
 273
 274 static inline void arch_bprm_mm_init(struct mm_struct *mm,
 275                 struct vm_area_struct *vma)
 276 {
 277         mpx_mm_init(mm);
 278 }
 279
 280 static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 281                               unsigned long start, unsigned long end)
 282 {
 283         /*
 284          * mpx_notify_unmap() goes and reads a rarely-hot
 285          * cacheline in the mm_struct.  That can be expensive
 286          * enough to be seen in profiles.
 287          *
 288          * The mpx_notify_unmap() call and its contents have been
 289          * observed to affect munmap() performance on hardware
 290          * where MPX is not present.
 291          *
 292          * The unlikely() optimizes for the fast case: no MPX
 293          * in the CPU, or no MPX use in the process.  Even if
 294          * we get this wrong (in the unlikely event that MPX
 295          * is widely enabled on some system) the overhead of
 296          * MPX itself (reading bounds tables) is expected to
 297          * overwhelm the overhead of getting this unlikely()
 298          * consistently wrong.
 299          */
 300         if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX)))
 301                 mpx_notify_unmap(mm, vma, start, end);
 302 }
 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 */