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KVM: MMU: Adjust shadow paging to work when SMEP=1 and CR0.WP=0

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When CR0.WP=0, we sometimes map user pages as kernel pages (to allow
the kernel to write to them).  Unfortunately this also allows the kernel
to fetch from these pages, even if CR4.SMEP is set.

Adjust for this by also setting NX on the spte in these circumstances.

Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Avi Kivity
2011-06-06 16:11:54 +03:00
parent a01c8f9b4e
commit 411c588dfb
3 changed files with 32 additions and 1 deletions
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14
arch/x86/kvm/mmu.c
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@ -1985,8 +1985,17 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
spte |= PT_WRITABLE_MASK;
if (!vcpu->arch.mmu.direct_map
&& !(pte_access & ACC_WRITE_MASK))
&& !(pte_access & ACC_WRITE_MASK)) {
spte &= ~PT_USER_MASK;
/*
* If we converted a user page to a kernel page,
* so that the kernel can write to it when cr0.wp=0,
* then we should prevent the kernel from executing it
* if SMEP is enabled.
*/
if (kvm_read_cr4_bits(vcpu, X86_CR4_SMEP))
spte |= PT64_NX_MASK;
}
/*
* Optimization: for pte sync, if spte was writable the hash
@ -2955,6 +2964,7 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
int kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
{
int r;
bool smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
ASSERT(vcpu);
ASSERT(!VALID_PAGE(vcpu->arch.mmu.root_hpa));
@ -2969,6 +2979,8 @@ int kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
vcpu->arch.mmu.base_role.cr4_pae = !!is_pae(vcpu);
vcpu->arch.mmu.base_role.cr0_wp = is_write_protection(vcpu);
vcpu->arch.mmu.base_role.smep_andnot_wp
= smep && !is_write_protection(vcpu);
return r;
}