KVM: x86: nSVM: skip eax alignment check for non-SVM instructions

BugLink: https://bugs.launchpad.net/bugs/1959879
commit 47c28d436f409f5b009dc82bd82d4971088aa391 upstream.

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@gmail.com>
Message-Id: <Yexlhaoe1Fscm59u@q>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e65755d6c247c2392e41c7ffb0b8c2c34b29db73..da33ec9bb26e82a0a9cc793ac5c0215f2f5d256f 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2238,10 +2238,6 @@ 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;
@@ -2259,8 +2255,13 @@ 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);