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[05/61] KVM: x86: Check userapce CPUID array size after validating sub-leaf

Message ID 20200201185218.24473-6-sean.j.christopherson@intel.com
State New, archived
Headers show
Series KVM: x86: Introduce KVM cpu caps | expand

Commit Message

Sean Christopherson Feb. 1, 2020, 6:51 p.m. UTC
Verify that the next sub-leaf of CPUID 0x4 (or 0x8000001d) is valid
before rejecting the entire KVM_GET_SUPPORTED_CPUID due to insufficent
space in the userspace array.

Note, although this is technically a bug, it's not visible to userspace
as KVM_GET_SUPPORTED_CPUID is guaranteed to fail on KVM_CPUID_SIGNATURE,
which is hardcoded to be added after the affected leafs.  The real
motivation for the change is to tightly couple the nent/maxnent and
do_host_cpuid() sequences in preparation for future cleanup.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/cpuid.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Vitaly Kuznetsov Feb. 6, 2020, 3:24 p.m. UTC | #1
Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Verify that the next sub-leaf of CPUID 0x4 (or 0x8000001d) is valid
> before rejecting the entire KVM_GET_SUPPORTED_CPUID due to insufficent
> space in the userspace array.
>
> Note, although this is technically a bug, it's not visible to userspace
> as KVM_GET_SUPPORTED_CPUID is guaranteed to fail on KVM_CPUID_SIGNATURE,
> which is hardcoded to be added after the affected leafs.  The real
> motivation for the change is to tightly couple the nent/maxnent and
> do_host_cpuid() sequences in preparation for future cleanup.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/cpuid.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 11d5f311ef10..e5cf1e0cf84a 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -552,12 +552,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
>  
>  		/* read more entries until cache_type is zero */
>  		for (i = 1; ; ++i) {
> -			if (*nent >= maxnent)
> -				goto out;
> -
>  			cache_type = entry[i - 1].eax & 0x1f;
>  			if (!cache_type)
>  				break;
> +
> +			if (*nent >= maxnent)
> +				goto out;
>  			do_host_cpuid(&entry[i], function, i);
>  			++*nent;
>  		}

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
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Patch

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 11d5f311ef10..e5cf1e0cf84a 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -552,12 +552,12 @@  static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 
 		/* read more entries until cache_type is zero */
 		for (i = 1; ; ++i) {
-			if (*nent >= maxnent)
-				goto out;
-
 			cache_type = entry[i - 1].eax & 0x1f;
 			if (!cache_type)
 				break;
+
+			if (*nent >= maxnent)
+				goto out;
 			do_host_cpuid(&entry[i], function, i);
 			++*nent;
 		}