The bug occurs on #GP triggered by VMware backdoor when eax value is
unaligned. eax alignment check should not be applied to non-SVM
instructions because it leads to incorrect omission of the instructions
emulation.
Apply the alignment check only to SVM instructions to fix.
Fixes: d1cba6c92237 ("KVM: x86: nSVM: test eax for 4K alignment for GP errata workaround")
Signed-off-by: Denis Valeev <lemniscattaden@xxxxxxxxx>
---
This bug breaks nyx-fuzz (https://nyx-fuzz.com) that uses VMware backdoor
as an alternative way for hypercall from guest user-mode. With this bug
a hypercall interpreted as a GP and leads to process termination.
arch/x86/kvm/svm/svm.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e64f16237b60..b5e4731080ef 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2233,10 +2233,6 @@ static int gp_interception(struct kvm_vcpu *vcpu)
if (error_code)
goto reinject;
- /* All SVM instructions expect page aligned RAX */
- if (svm->vmcb->save.rax & ~PAGE_MASK)
- goto reinject;
-
/* Decode the instruction for usage later */
if (x86_decode_emulated_instruction(vcpu, 0, NULL, 0) != EMULATION_OK)
goto reinject;
@@ -2254,8 +2250,13 @@ static int gp_interception(struct kvm_vcpu *vcpu)
if (!is_guest_mode(vcpu))
return kvm_emulate_instruction(vcpu,
EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE);
- } else
+ } else {
+ /* All SVM instructions expect page aligned RAX */
+ if (svm->vmcb->save.rax & ~PAGE_MASK)
+ goto reinject;
+
return emulate_svm_instr(vcpu, opcode);
+ }
reinject:
kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
--
2.34.1
