Re: [PATCH] kvm/x86: actually verify that reading MSR_IA32_UCODE_REV succeeds
From: Daniil Tatianin
Date: Thu Mar 16 2023 - 01:51:32 EST
On 3/15/23 11:16 PM, Sean Christopherson wrote:
On Wed, Mar 15, 2023, Daniil Tatianin wrote:
...and return KVM_MSR_RET_INVALID otherwise.
Found by Linux Verification Center (linuxtesting.org) with the SVACE
static analysis tool.
Fixes: cd28325249a1 ("KVM: VMX: support MSR_IA32_ARCH_CAPABILITIES as a feature MSR")
Signed-off-by: Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7713420abab0..7de6939fc371 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1661,7 +1661,8 @@ static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
msr->data = kvm_caps.supported_perf_cap;
break;
case MSR_IA32_UCODE_REV:
- rdmsrl_safe(msr->index, &msr->data);
+ if (rdmsrl_safe(msr->index, &msr->data))
+ return KVM_MSR_RET_INVALID;
This is unnecessary and would arguably break KVM's ABI. KVM unconditionally emulates
MSR_IA32_UCODE_REV in software and rdmsrl_safe() zeros the result on a fault (see
ex_handler_msr()). '0' is a legitimate ucode revid and a reasonable fallback for
a theoretical (virtual) CPU that doesn't support the MSR.
I see, thanks for the explanation!