linux/arch/x86/include/asm/mmu_context.h
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   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#include <asm/debugreg.h>
  17
  18extern atomic64_t last_mm_ctx_id;
  19
  20#ifndef CONFIG_PARAVIRT_XXL
  21static inline void paravirt_activate_mm(struct mm_struct *prev,
  22                                        struct mm_struct *next)
  23{
  24}
  25#endif  /* !CONFIG_PARAVIRT_XXL */
  26
  27#ifdef CONFIG_PERF_EVENTS
  28
  29DECLARE_STATIC_KEY_FALSE(rdpmc_always_available_key);
  30
  31static inline void load_mm_cr4_irqsoff(struct mm_struct *mm)
  32{
  33        if (static_branch_unlikely(&rdpmc_always_available_key) ||
  34            atomic_read(&mm->context.perf_rdpmc_allowed))
  35                cr4_set_bits_irqsoff(X86_CR4_PCE);
  36        else
  37                cr4_clear_bits_irqsoff(X86_CR4_PCE);
  38}
  39#else
  40static inline void load_mm_cr4_irqsoff(struct mm_struct *mm) {}
  41#endif
  42
  43#ifdef CONFIG_MODIFY_LDT_SYSCALL
  44/*
  45 * ldt_structs can be allocated, used, and freed, but they are never
  46 * modified while live.
  47 */
  48struct ldt_struct {
  49        /*
  50         * Xen requires page-aligned LDTs with special permissions.  This is
  51         * needed to prevent us from installing evil descriptors such as
  52         * call gates.  On native, we could merge the ldt_struct and LDT
  53         * allocations, but it's not worth trying to optimize.
  54         */
  55        struct desc_struct      *entries;
  56        unsigned int            nr_entries;
  57
  58        /*
  59         * If PTI is in use, then the entries array is not mapped while we're
  60         * in user mode.  The whole array will be aliased at the addressed
  61         * given by ldt_slot_va(slot).  We use two slots so that we can allocate
  62         * and map, and enable a new LDT without invalidating the mapping
  63         * of an older, still-in-use LDT.
  64         *
  65         * slot will be -1 if this LDT doesn't have an alias mapping.
  66         */
  67        int                     slot;
  68};
  69
  70/* This is a multiple of PAGE_SIZE. */
  71#define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
  72
  73static inline void *ldt_slot_va(int slot)
  74{
  75        return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
  76}
  77
  78/*
  79 * Used for LDT copy/destruction.
  80 */
  81static inline void init_new_context_ldt(struct mm_struct *mm)
  82{
  83        mm->context.ldt = NULL;
  84        init_rwsem(&mm->context.ldt_usr_sem);
  85}
  86int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm);
  87void destroy_context_ldt(struct mm_struct *mm);
  88void ldt_arch_exit_mmap(struct mm_struct *mm);
  89#else   /* CONFIG_MODIFY_LDT_SYSCALL */
  90static inline void init_new_context_ldt(struct mm_struct *mm) { }
  91static inline int ldt_dup_context(struct mm_struct *oldmm,
  92                                  struct mm_struct *mm)
  93{
  94        return 0;
  95}
  96static inline void destroy_context_ldt(struct mm_struct *mm) { }
  97static inline void ldt_arch_exit_mmap(struct mm_struct *mm) { }
  98#endif
  99
 100static inline void load_mm_ldt(struct mm_struct *mm)
 101{
 102#ifdef CONFIG_MODIFY_LDT_SYSCALL
 103        struct ldt_struct *ldt;
 104
 105        /* READ_ONCE synchronizes with smp_store_release */
 106        ldt = READ_ONCE(mm->context.ldt);
 107
 108        /*
 109         * Any change to mm->context.ldt is followed by an IPI to all
 110         * CPUs with the mm active.  The LDT will not be freed until
 111         * after the IPI is handled by all such CPUs.  This means that,
 112         * if the ldt_struct changes before we return, the values we see
 113         * will be safe, and the new values will be loaded before we run
 114         * any user code.
 115         *
 116         * NB: don't try to convert this to use RCU without extreme care.
 117         * We would still need IRQs off, because we don't want to change
 118         * the local LDT after an IPI loaded a newer value than the one
 119         * that we can see.
 120         */
 121
 122        if (unlikely(ldt)) {
 123                if (static_cpu_has(X86_FEATURE_PTI)) {
 124                        if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) {
 125                                /*
 126                                 * Whoops -- either the new LDT isn't mapped
 127                                 * (if slot == -1) or is mapped into a bogus
 128                                 * slot (if slot > 1).
 129                                 */
 130                                clear_LDT();
 131                                return;
 132                        }
 133
 134                        /*
 135                         * If page table isolation is enabled, ldt->entries
 136                         * will not be mapped in the userspace pagetables.
 137                         * Tell the CPU to access the LDT through the alias
 138                         * at ldt_slot_va(ldt->slot).
 139                         */
 140                        set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries);
 141                } else {
 142                        set_ldt(ldt->entries, ldt->nr_entries);
 143                }
 144        } else {
 145                clear_LDT();
 146        }
 147#else
 148        clear_LDT();
 149#endif
 150}
 151
 152static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
 153{
 154#ifdef CONFIG_MODIFY_LDT_SYSCALL
 155        /*
 156         * Load the LDT if either the old or new mm had an LDT.
 157         *
 158         * An mm will never go from having an LDT to not having an LDT.  Two
 159         * mms never share an LDT, so we don't gain anything by checking to
 160         * see whether the LDT changed.  There's also no guarantee that
 161         * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
 162         * then prev->context.ldt will also be non-NULL.
 163         *
 164         * If we really cared, we could optimize the case where prev == next
 165         * and we're exiting lazy mode.  Most of the time, if this happens,
 166         * we don't actually need to reload LDTR, but modify_ldt() is mostly
 167         * used by legacy code and emulators where we don't need this level of
 168         * performance.
 169         *
 170         * This uses | instead of || because it generates better code.
 171         */
 172        if (unlikely((unsigned long)prev->context.ldt |
 173                     (unsigned long)next->context.ldt))
 174                load_mm_ldt(next);
 175#endif
 176
 177        DEBUG_LOCKS_WARN_ON(preemptible());
 178}
 179
 180void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
 181
 182/*
 183 * Init a new mm.  Used on mm copies, like at fork()
 184 * and on mm's that are brand-new, like at execve().
 185 */
 186static inline int init_new_context(struct task_struct *tsk,
 187                                   struct mm_struct *mm)
 188{
 189        mutex_init(&mm->context.lock);
 190
 191        mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id);
 192        atomic64_set(&mm->context.tlb_gen, 0);
 193
 194#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 195        if (cpu_feature_enabled(X86_FEATURE_OSPKE)) {
 196                /* pkey 0 is the default and allocated implicitly */
 197                mm->context.pkey_allocation_map = 0x1;
 198                /* -1 means unallocated or invalid */
 199                mm->context.execute_only_pkey = -1;
 200        }
 201#endif
 202        init_new_context_ldt(mm);
 203        return 0;
 204}
 205static inline void destroy_context(struct mm_struct *mm)
 206{
 207        destroy_context_ldt(mm);
 208}
 209
 210extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 211                      struct task_struct *tsk);
 212
 213extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 214                               struct task_struct *tsk);
 215#define switch_mm_irqs_off switch_mm_irqs_off
 216
 217#define activate_mm(prev, next)                 \
 218do {                                            \
 219        paravirt_activate_mm((prev), (next));   \
 220        switch_mm((prev), (next), NULL);        \
 221} while (0);
 222
 223#ifdef CONFIG_X86_32
 224#define deactivate_mm(tsk, mm)                  \
 225do {                                            \
 226        lazy_load_gs(0);                        \
 227} while (0)
 228#else
 229#define deactivate_mm(tsk, mm)                  \
 230do {                                            \
 231        load_gs_index(0);                       \
 232        loadsegment(fs, 0);                     \
 233} while (0)
 234#endif
 235
 236static inline void arch_dup_pkeys(struct mm_struct *oldmm,
 237                                  struct mm_struct *mm)
 238{
 239#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
 240        if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
 241                return;
 242
 243        /* Duplicate the oldmm pkey state in mm: */
 244        mm->context.pkey_allocation_map = oldmm->context.pkey_allocation_map;
 245        mm->context.execute_only_pkey   = oldmm->context.execute_only_pkey;
 246#endif
 247}
 248
 249static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
 250{
 251        arch_dup_pkeys(oldmm, mm);
 252        paravirt_arch_dup_mmap(oldmm, mm);
 253        return ldt_dup_context(oldmm, mm);
 254}
 255
 256static inline void arch_exit_mmap(struct mm_struct *mm)
 257{
 258        paravirt_arch_exit_mmap(mm);
 259        ldt_arch_exit_mmap(mm);
 260}
 261
 262#ifdef CONFIG_X86_64
 263static inline bool is_64bit_mm(struct mm_struct *mm)
 264{
 265        return  !IS_ENABLED(CONFIG_IA32_EMULATION) ||
 266                !(mm->context.ia32_compat == TIF_IA32);
 267}
 268#else
 269static inline bool is_64bit_mm(struct mm_struct *mm)
 270{
 271        return false;
 272}
 273#endif
 274
 275static inline void arch_bprm_mm_init(struct mm_struct *mm,
 276                struct vm_area_struct *vma)
 277{
 278        mpx_mm_init(mm);
 279}
 280
 281static inline void arch_unmap(struct mm_struct *mm, unsigned long start,
 282                              unsigned long end)
 283{
 284        /*
 285         * mpx_notify_unmap() goes and reads a rarely-hot
 286         * cacheline in the mm_struct.  That can be expensive
 287         * enough to be seen in profiles.
 288         *
 289         * The mpx_notify_unmap() call and its contents have been
 290         * observed to affect munmap() performance on hardware
 291         * where MPX is not present.
 292         *
 293         * The unlikely() optimizes for the fast case: no MPX
 294         * in the CPU, or no MPX use in the process.  Even if
 295         * we get this wrong (in the unlikely event that MPX
 296         * is widely enabled on some system) the overhead of
 297         * MPX itself (reading bounds tables) is expected to
 298         * overwhelm the overhead of getting this unlikely()
 299         * consistently wrong.
 300         */
 301        if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX)))
 302                mpx_notify_unmap(mm, start, end);
 303}
 304
 305/*
 306 * We only want to enforce protection keys on the current process
 307 * because we effectively have no access to PKRU for other
 308 * processes or any way to tell *which * PKRU in a threaded
 309 * process we could use.
 310 *
 311 * So do not enforce things if the VMA is not from the current
 312 * mm, or if we are in a kernel thread.
 313 */
 314static inline bool vma_is_foreign(struct vm_area_struct *vma)
 315{
 316        if (!current->mm)
 317                return true;
 318        /*
 319         * Should PKRU be enforced on the access to this VMA?  If
 320         * the VMA is from another process, then PKRU has no
 321         * relevance and should not be enforced.
 322         */
 323        if (current->mm != vma->vm_mm)
 324                return true;
 325
 326        return false;
 327}
 328
 329static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 330                bool write, bool execute, bool foreign)
 331{
 332        /* pkeys never affect instruction fetches */
 333        if (execute)
 334                return true;
 335        /* allow access if the VMA is not one from this process */
 336        if (foreign || vma_is_foreign(vma))
 337                return true;
 338        return __pkru_allows_pkey(vma_pkey(vma), write);
 339}
 340
 341/*
 342 * This can be used from process context to figure out what the value of
 343 * CR3 is without needing to do a (slow) __read_cr3().
 344 *
 345 * It's intended to be used for code like KVM that sneakily changes CR3
 346 * and needs to restore it.  It needs to be used very carefully.
 347 */
 348static inline unsigned long __get_current_cr3_fast(void)
 349{
 350        unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
 351                this_cpu_read(cpu_tlbstate.loaded_mm_asid));
 352
 353        /* For now, be very restrictive about when this can be called. */
 354        VM_WARN_ON(in_nmi() || preemptible());
 355
 356        VM_BUG_ON(cr3 != __read_cr3());
 357        return cr3;
 358}
 359
 360typedef struct {
 361        struct mm_struct *mm;
 362} temp_mm_state_t;
 363
 364/*
 365 * Using a temporary mm allows to set temporary mappings that are not accessible
 366 * by other CPUs. Such mappings are needed to perform sensitive memory writes
 367 * that override the kernel memory protections (e.g., W^X), without exposing the
 368 * temporary page-table mappings that are required for these write operations to
 369 * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
 370 * mapping is torn down.
 371 *
 372 * Context: The temporary mm needs to be used exclusively by a single core. To
 373 *          harden security IRQs must be disabled while the temporary mm is
 374 *          loaded, thereby preventing interrupt handler bugs from overriding
 375 *          the kernel memory protection.
 376 */
 377static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
 378{
 379        temp_mm_state_t temp_state;
 380
 381        lockdep_assert_irqs_disabled();
 382        temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
 383        switch_mm_irqs_off(NULL, mm, current);
 384
 385        /*
 386         * If breakpoints are enabled, disable them while the temporary mm is
 387         * used. Userspace might set up watchpoints on addresses that are used
 388         * in the temporary mm, which would lead to wrong signals being sent or
 389         * crashes.
 390         *
 391         * Note that breakpoints are not disabled selectively, which also causes
 392         * kernel breakpoints (e.g., perf's) to be disabled. This might be
 393         * undesirable, but still seems reasonable as the code that runs in the
 394         * temporary mm should be short.
 395         */
 396        if (hw_breakpoint_active())
 397                hw_breakpoint_disable();
 398
 399        return temp_state;
 400}
 401
 402static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
 403{
 404        lockdep_assert_irqs_disabled();
 405        switch_mm_irqs_off(NULL, prev_state.mm, current);
 406
 407        /*
 408         * Restore the breakpoints if they were disabled before the temporary mm
 409         * was loaded.
 410         */
 411        if (hw_breakpoint_active())
 412                hw_breakpoint_restore();
 413}
 414
 415#endif /* _ASM_X86_MMU_CONTEXT_H */
 416