x86/ldt: Rework locking

[linux/fpc-iii.git] / arch / x86 / include / asm / mmu_context.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_MMU_CONTEXT_H
#define _ASM_X86_MMU_CONTEXT_H

#include <asm/desc.h>
#include <linux/atomic.h>
#include <linux/mm_types.h>
#include <linux/pkeys.h>

#include <trace/events/tlb.h>

#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/paravirt.h>
#include <asm/mpx.h>

extern atomic64_t last_mm_ctx_id;

#ifndef CONFIG_PARAVIRT
static inline void paravirt_activate_mm(struct mm_struct *prev,
                                        struct mm_struct *next)
{
}
#endif  /* !CONFIG_PARAVIRT */

#ifdef CONFIG_PERF_EVENTS
extern struct static_key rdpmc_always_available;

static inline void load_mm_cr4(struct mm_struct *mm)
{
        if (static_key_false(&rdpmc_always_available) ||
            atomic_read(&mm->context.perf_rdpmc_allowed))
                cr4_set_bits(X86_CR4_PCE);
        else
                cr4_clear_bits(X86_CR4_PCE);
}
#else
static inline void load_mm_cr4(struct mm_struct *mm) {}
#endif

#ifdef CONFIG_MODIFY_LDT_SYSCALL
/*
 * ldt_structs can be allocated, used, and freed, but they are never
 * modified while live.
 */
struct ldt_struct {
        /*
         * Xen requires page-aligned LDTs with special permissions.  This is
         * needed to prevent us from installing evil descriptors such as
         * call gates.  On native, we could merge the ldt_struct and LDT
         * allocations, but it's not worth trying to optimize.
         */
        struct desc_struct *entries;
        unsigned int nr_entries;
};

/*
 * Used for LDT copy/destruction.
 */
int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm);
void destroy_context_ldt(struct mm_struct *mm);
#else   /* CONFIG_MODIFY_LDT_SYSCALL */
static inline int init_new_context_ldt(struct task_struct *tsk,
                                       struct mm_struct *mm)
{
        return 0;
}
static inline void destroy_context_ldt(struct mm_struct *mm) {}
#endif

static inline void load_mm_ldt(struct mm_struct *mm)
{
#ifdef CONFIG_MODIFY_LDT_SYSCALL
        struct ldt_struct *ldt;

        /* READ_ONCE synchronizes with smp_store_release */
        ldt = READ_ONCE(mm->context.ldt);

        /*
         * Any change to mm->context.ldt is followed by an IPI to all
         * CPUs with the mm active.  The LDT will not be freed until
         * after the IPI is handled by all such CPUs.  This means that,
         * if the ldt_struct changes before we return, the values we see
         * will be safe, and the new values will be loaded before we run
         * any user code.
         *
         * NB: don't try to convert this to use RCU without extreme care.
         * We would still need IRQs off, because we don't want to change
         * the local LDT after an IPI loaded a newer value than the one
         * that we can see.
         */

        if (unlikely(ldt))
                set_ldt(ldt->entries, ldt->nr_entries);
        else
                clear_LDT();
#else
        clear_LDT();
#endif
}

static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
{
#ifdef CONFIG_MODIFY_LDT_SYSCALL
        /*
         * Load the LDT if either the old or new mm had an LDT.
         *
         * An mm will never go from having an LDT to not having an LDT.  Two
         * mms never share an LDT, so we don't gain anything by checking to
         * see whether the LDT changed.  There's also no guarantee that
         * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
         * then prev->context.ldt will also be non-NULL.
         *
         * If we really cared, we could optimize the case where prev == next
         * and we're exiting lazy mode.  Most of the time, if this happens,
         * we don't actually need to reload LDTR, but modify_ldt() is mostly
         * used by legacy code and emulators where we don't need this level of
         * performance.
         *
         * This uses | instead of || because it generates better code.
         */
        if (unlikely((unsigned long)prev->context.ldt |
                     (unsigned long)next->context.ldt))
                load_mm_ldt(next);
#endif

        DEBUG_LOCKS_WARN_ON(preemptible());
}

void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);

static inline int init_new_context(struct task_struct *tsk,
                                   struct mm_struct *mm)
{
        mutex_init(&mm->context.lock);

        mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id);
        atomic64_set(&mm->context.tlb_gen, 0);

        #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
        if (cpu_feature_enabled(X86_FEATURE_OSPKE)) {
                /* pkey 0 is the default and always allocated */
                mm->context.pkey_allocation_map = 0x1;
                /* -1 means unallocated or invalid */
                mm->context.execute_only_pkey = -1;
        }
        #endif
        return init_new_context_ldt(tsk, mm);
}
static inline void destroy_context(struct mm_struct *mm)
{
        destroy_context_ldt(mm);
}

extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
                      struct task_struct *tsk);

extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
                               struct task_struct *tsk);
#define switch_mm_irqs_off switch_mm_irqs_off

#define activate_mm(prev, next)                 \
do {                                            \
        paravirt_activate_mm((prev), (next));   \
        switch_mm((prev), (next), NULL);        \
} while (0);

#ifdef CONFIG_X86_32
#define deactivate_mm(tsk, mm)                  \
do {                                            \
        lazy_load_gs(0);                        \
} while (0)
#else
#define deactivate_mm(tsk, mm)                  \
do {                                            \
        load_gs_index(0);                       \
        loadsegment(fs, 0);                     \
} while (0)
#endif

static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
{
        paravirt_arch_dup_mmap(oldmm, mm);
        return 0;
}

static inline void arch_exit_mmap(struct mm_struct *mm)
{
        paravirt_arch_exit_mmap(mm);
}

#ifdef CONFIG_X86_64
static inline bool is_64bit_mm(struct mm_struct *mm)
{
        return  !IS_ENABLED(CONFIG_IA32_EMULATION) ||
                !(mm->context.ia32_compat == TIF_IA32);
}
#else
static inline bool is_64bit_mm(struct mm_struct *mm)
{
        return false;
}
#endif

static inline void arch_bprm_mm_init(struct mm_struct *mm,
                struct vm_area_struct *vma)
{
        mpx_mm_init(mm);
}

static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
                              unsigned long start, unsigned long end)
{
        /*
         * mpx_notify_unmap() goes and reads a rarely-hot
         * cacheline in the mm_struct.  That can be expensive
         * enough to be seen in profiles.
         *
         * The mpx_notify_unmap() call and its contents have been
         * observed to affect munmap() performance on hardware
         * where MPX is not present.
         *
         * The unlikely() optimizes for the fast case: no MPX
         * in the CPU, or no MPX use in the process.  Even if
         * we get this wrong (in the unlikely event that MPX
         * is widely enabled on some system) the overhead of
         * MPX itself (reading bounds tables) is expected to
         * overwhelm the overhead of getting this unlikely()
         * consistently wrong.
         */
        if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX)))
                mpx_notify_unmap(mm, vma, start, end);
}

#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
static inline int vma_pkey(struct vm_area_struct *vma)
{
        unsigned long vma_pkey_mask = VM_PKEY_BIT0 | VM_PKEY_BIT1 |
                                      VM_PKEY_BIT2 | VM_PKEY_BIT3;

        return (vma->vm_flags & vma_pkey_mask) >> VM_PKEY_SHIFT;
}
#else
static inline int vma_pkey(struct vm_area_struct *vma)
{
        return 0;
}
#endif

/*
 * We only want to enforce protection keys on the current process
 * because we effectively have no access to PKRU for other
 * processes or any way to tell *which * PKRU in a threaded
 * process we could use.
 *
 * So do not enforce things if the VMA is not from the current
 * mm, or if we are in a kernel thread.
 */
static inline bool vma_is_foreign(struct vm_area_struct *vma)
{
        if (!current->mm)
                return true;
        /*
         * Should PKRU be enforced on the access to this VMA?  If
         * the VMA is from another process, then PKRU has no
         * relevance and should not be enforced.
         */
        if (current->mm != vma->vm_mm)
                return true;

        return false;
}

static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
                bool write, bool execute, bool foreign)
{
        /* pkeys never affect instruction fetches */
        if (execute)
                return true;
        /* allow access if the VMA is not one from this process */
        if (foreign || vma_is_foreign(vma))
                return true;
        return __pkru_allows_pkey(vma_pkey(vma), write);
}

/*
 * If PCID is on, ASID-aware code paths put the ASID+1 into the PCID
 * bits.  This serves two purposes.  It prevents a nasty situation in
 * which PCID-unaware code saves CR3, loads some other value (with PCID
 * == 0), and then restores CR3, thus corrupting the TLB for ASID 0 if
 * the saved ASID was nonzero.  It also means that any bugs involving
 * loading a PCID-enabled CR3 with CR4.PCIDE off will trigger
 * deterministically.
 */

static inline unsigned long build_cr3(struct mm_struct *mm, u16 asid)
{
        if (static_cpu_has(X86_FEATURE_PCID)) {
                VM_WARN_ON_ONCE(asid > 4094);
                return __sme_pa(mm->pgd) | (asid + 1);
        } else {
                VM_WARN_ON_ONCE(asid != 0);
                return __sme_pa(mm->pgd);
        }
}

static inline unsigned long build_cr3_noflush(struct mm_struct *mm, u16 asid)
{
        VM_WARN_ON_ONCE(asid > 4094);
        return __sme_pa(mm->pgd) | (asid + 1) | CR3_NOFLUSH;
}

/*
 * This can be used from process context to figure out what the value of
 * CR3 is without needing to do a (slow) __read_cr3().
 *
 * It's intended to be used for code like KVM that sneakily changes CR3
 * and needs to restore it.  It needs to be used very carefully.
 */
static inline unsigned long __get_current_cr3_fast(void)
{
        unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm),
                this_cpu_read(cpu_tlbstate.loaded_mm_asid));

        /* For now, be very restrictive about when this can be called. */
        VM_WARN_ON(in_nmi() || preemptible());

        VM_BUG_ON(cr3 != __read_cr3());
        return cr3;
}

#endif /* _ASM_X86_MMU_CONTEXT_H */