mmu_audit.c

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/*
 * mmu_audit.c:
 *
 * Audit code for KVM MMU
 *
 * Copyright (C) 2006 Qumranet, Inc.
 * Copyright 2010 Red Hat, Inc. and/or its affiliates.
 *
 * Authors:
 *   Yaniv Kamay  <[email protected]>
 *   Avi Kivity   <[email protected]>
 *   Marcelo Tosatti <[email protected]>
 *   Xiao Guangrong <[email protected]>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 */

#include <linux/ratelimit.h>

char const *audit_point_name[] = {
    "pre page fault",
    "post page fault",
    "pre pte write",
    "post pte write",
    "pre sync",
    "post sync"
};

#define audit_printk(kvm, fmt, args...)     \
    printk(KERN_ERR "audit: (%s) error: "   \
        fmt, audit_point_name[kvm->arch.audit_point], ##args)

typedef void (*inspect_spte_fn) (struct kvm_vcpu *vcpu, u64 *sptep, int level);

static void __mmu_spte_walk(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
                inspect_spte_fn fn, int level)
{
    int i;

    for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
        u64 *ent = sp->spt;

        fn(vcpu, ent + i, level);

        if (is_shadow_present_pte(ent[i]) &&
              !is_last_spte(ent[i], level)) {
            struct kvm_mmu_page *child;

            child = page_header(ent[i] & PT64_BASE_ADDR_MASK);
            __mmu_spte_walk(vcpu, child, fn, level - 1);
        }
    }
}

static void mmu_spte_walk(struct kvm_vcpu *vcpu, inspect_spte_fn fn)
{
    int i;
    struct kvm_mmu_page *sp;

    if (!VALID_PAGE(vcpu->arch.mmu.root_hpa))
        return;

    if (vcpu->arch.mmu.root_level == PT64_ROOT_LEVEL) {
        hpa_t root = vcpu->arch.mmu.root_hpa;

        sp = page_header(root);
        __mmu_spte_walk(vcpu, sp, fn, PT64_ROOT_LEVEL);
        return;
    }

    for (i = 0; i < 4; ++i) {
        hpa_t root = vcpu->arch.mmu.pae_root[i];

        if (root && VALID_PAGE(root)) {
            root &= PT64_BASE_ADDR_MASK;
            sp = page_header(root);
            __mmu_spte_walk(vcpu, sp, fn, 2);
        }
    }

    return;
}

typedef void (*sp_handler) (struct kvm *kvm, struct kvm_mmu_page *sp);

static void walk_all_active_sps(struct kvm *kvm, sp_handler fn)
{
    struct kvm_mmu_page *sp;

    list_for_each_entry(sp, &kvm->arch.active_mmu_pages, link)
        fn(kvm, sp);
}

static void audit_mappings(struct kvm_vcpu *vcpu, u64 *sptep, int level)
{
    struct kvm_mmu_page *sp;
    gfn_t gfn;
    pfn_t pfn;
    hpa_t hpa;

    sp = page_header(__pa(sptep));

    if (sp->unsync) {
        if (level != PT_PAGE_TABLE_LEVEL) {
            audit_printk(vcpu->kvm, "unsync sp: %p "
                     "level = %d\n", sp, level);
            return;
        }
    }

    if (!is_shadow_present_pte(*sptep) || !is_last_spte(*sptep, level))
        return;

    gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
    pfn = gfn_to_pfn_atomic(vcpu->kvm, gfn);

    if (is_error_pfn(pfn))
        return;

    hpa =  pfn << PAGE_SHIFT;
    if ((*sptep & PT64_BASE_ADDR_MASK) != hpa)
        audit_printk(vcpu->kvm, "levels %d pfn %llx hpa %llx "
                 "ent %llxn", vcpu->arch.mmu.root_level, pfn,
                 hpa, *sptep);
}

static void inspect_spte_has_rmap(struct kvm *kvm, u64 *sptep)
{
    static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
    unsigned long *rmapp;
    struct kvm_mmu_page *rev_sp;
    gfn_t gfn;

    rev_sp = page_header(__pa(sptep));
    gfn = kvm_mmu_page_get_gfn(rev_sp, sptep - rev_sp->spt);

    if (!gfn_to_memslot(kvm, gfn)) {
        if (!__ratelimit(&ratelimit_state))
            return;
        audit_printk(kvm, "no memslot for gfn %llx\n", gfn);
        audit_printk(kvm, "index %ld of sp (gfn=%llx)\n",
               (long int)(sptep - rev_sp->spt), rev_sp->gfn);
        dump_stack();
        return;
    }

    rmapp = gfn_to_rmap(kvm, gfn, rev_sp->role.level);
    if (!*rmapp) {
        if (!__ratelimit(&ratelimit_state))
            return;
        audit_printk(kvm, "no rmap for writable spte %llx\n",
                 *sptep);
        dump_stack();
    }
}

static void audit_sptes_have_rmaps(struct kvm_vcpu *vcpu, u64 *sptep, int level)
{
    if (is_shadow_present_pte(*sptep) && is_last_spte(*sptep, level))
        inspect_spte_has_rmap(vcpu->kvm, sptep);
}

static void audit_spte_after_sync(struct kvm_vcpu *vcpu, u64 *sptep, int level)
{
    struct kvm_mmu_page *sp = page_header(__pa(sptep));

    if (vcpu->kvm->arch.audit_point == AUDIT_POST_SYNC && sp->unsync)
        audit_printk(vcpu->kvm, "meet unsync sp(%p) after sync "
                 "root.\n", sp);
}

static void check_mappings_rmap(struct kvm *kvm, struct kvm_mmu_page *sp)
{
    int i;

    if (sp->role.level != PT_PAGE_TABLE_LEVEL)
        return;

    for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
        if (!is_rmap_spte(sp->spt[i]))
            continue;

        inspect_spte_has_rmap(kvm, sp->spt + i);
    }
}

static void audit_write_protection(struct kvm *kvm, struct kvm_mmu_page *sp)
{
    unsigned long *rmapp;
    u64 *sptep;
    struct rmap_iterator iter;

    if (sp->role.direct || sp->unsync || sp->role.invalid)
        return;

    rmapp = gfn_to_rmap(kvm, sp->gfn, PT_PAGE_TABLE_LEVEL);

    for (sptep = rmap_get_first(*rmapp, &iter); sptep;
         sptep = rmap_get_next(&iter)) {
        if (is_writable_pte(*sptep))
            audit_printk(kvm, "shadow page has writable "
                     "mappings: gfn %llx role %x\n",
                     sp->gfn, sp->role.word);
    }
}

static void audit_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
{
    check_mappings_rmap(kvm, sp);
    audit_write_protection(kvm, sp);
}

static void audit_all_active_sps(struct kvm *kvm)
{
    walk_all_active_sps(kvm, audit_sp);
}

static void audit_spte(struct kvm_vcpu *vcpu, u64 *sptep, int level)
{
    audit_sptes_have_rmaps(vcpu, sptep, level);
    audit_mappings(vcpu, sptep, level);
    audit_spte_after_sync(vcpu, sptep, level);
}

static void audit_vcpu_spte(struct kvm_vcpu *vcpu)
{
    mmu_spte_walk(vcpu, audit_spte);
}

static bool mmu_audit;
static struct static_key mmu_audit_key;

static void __kvm_mmu_audit(struct kvm_vcpu *vcpu, int point)
{
    static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);

    if (!__ratelimit(&ratelimit_state))
        return;

    vcpu->kvm->arch.audit_point = point;
    audit_all_active_sps(vcpu->kvm);
    audit_vcpu_spte(vcpu);
}

static inline void kvm_mmu_audit(struct kvm_vcpu *vcpu, int point)
{
    if (static_key_false((&mmu_audit_key)))
        __kvm_mmu_audit(vcpu, point);
}

static void mmu_audit_enable(void)
{
    if (mmu_audit)
        return;

    static_key_slow_inc(&mmu_audit_key);
    mmu_audit = true;
}

static void mmu_audit_disable(void)
{
    if (!mmu_audit)
        return;

    static_key_slow_dec(&mmu_audit_key);
    mmu_audit = false;
}

static int mmu_audit_set(const char *val, const struct kernel_param *kp)
{
    int ret;
    unsigned long enable;

    ret = strict_strtoul(val, 10, &enable);
    if (ret < 0)
        return -EINVAL;

    switch (enable) {
    case 0:
        mmu_audit_disable();
        break;
    case 1:
        mmu_audit_enable();
        break;
    default:
        return -EINVAL;
    }

    return 0;
}

static struct kernel_param_ops audit_param_ops = {
    .set = mmu_audit_set,
    .get = param_get_bool,
};

module_param_cb(mmu_audit, &audit_param_ops, &mmu_audit, 0644);