[PATCH MANUALSEL 5.10 5/6] KVM: SVM: Don't kill SEV guest if SMAP erratum triggers in usermode

Sasha Levin
2022-02-09T18:59:07Z

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit cdf85e0c5dc766fc7fc779466280e454a6d04f87 ]

Inject a #GP instead of synthesizing triple fault to try to avoid killing
the guest if emulation of an SEV guest fails due to encountering the SMAP
erratum. The injected #GP may still be fatal to the guest, e.g. if the
userspace process is providing critical functionality, but KVM should
make every attempt to keep the guest alive.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Message-Id: <20220120010719.711476-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/svm/svm.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fa543c355fbdb..d515c8e68314c 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4155,7 +4155,21 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int i
return true;

pr_err_ratelimited("KVM: SEV Guest triggered AMD Erratum 1096\n");
- kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+
+ /*
+ * If the fault occurred in userspace, arbitrarily inject #GP
+ * to avoid killing the guest and to hopefully avoid confusing
+ * the guest kernel too much, e.g. injecting #PF would not be
+ * coherent with respect to the guest's page tables. Request
+ * triple fault if the fault occurred in the kernel as there's
+ * no fault that KVM can inject without confusing the guest.
+ * In practice, the triple fault is moot as no sane SEV kernel
+ * will execute from user memory while also running with SMAP=1.
+ */
+ if (is_user)
+ kvm_inject_gp(vcpu, 0);
+ else
+ kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
}

return false;
--
2.34.1