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KVM: VMX: do not use uninitialized gfn_to_hva_cache

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An uninitialized gfn_to_hva_cache has ghc->len == 0, which causes
the accessors to croak very loudly.  While a BUG_ON is definitely
_too_ loud and a bug on its own, there is indeed an issue of using
the caches in such a way that they could not have been initialized,
because ghc->gpa == 0 might match and thus kvm_gfn_to_hva_cache_init
would not be called.

For the vmcs12_cache, the solution is simply to invoke
kvm_gfn_to_hva_cache_init unconditionally: we already know
that the cache does not match the current VMCS pointer.
For the shadow_vmcs12_cache, there is no similar condition
that checks the VMCS link pointer, so invalidate the cache
on VMXON.

Fixes: cee66664dcd6 ("KVM: nVMX: Use a gfn_to_hva_cache for vmptrld")
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Reported-by: syzbot+7b7db8bb4db6fd5e157b@syzkaller.appspotmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2021-11-22 18:20:16 -05:00
parent d5d1cf47d1
commit 8503fea676
1 changed files with 2 additions and 2 deletions
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4
arch/x86/kvm/vmx/nested.c
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@ -4857,6 +4857,7 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
if (!vmx->nested.cached_vmcs12)
goto out_cached_vmcs12;
vmx->nested.shadow_vmcs12_cache.gpa = INVALID_GPA;
vmx->nested.cached_shadow_vmcs12 = kzalloc(VMCS12_SIZE, GFP_KERNEL_ACCOUNT);
if (!vmx->nested.cached_shadow_vmcs12)
goto out_cached_shadow_vmcs12;
@ -5289,8 +5290,7 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
struct gfn_to_hva_cache *ghc = &vmx->nested.vmcs12_cache;
struct vmcs_hdr hdr;
if (ghc->gpa != vmptr &&
kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, vmptr, VMCS12_SIZE)) {
if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, vmptr, VMCS12_SIZE)) {
/*
* Reads from an unbacked page return all 1s,
* which means that the 32 bits located at the