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Date: Wed, 9 Feb 2022 13:56:50 -0500 From: Sasha Levin <sashal@...nel.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Sean Christopherson <seanjc@...gle.com>, Liam Merwick <liam.merwick@...cle.com>, Paolo Bonzini <pbonzini@...hat.com>, Sasha Levin <sashal@...nel.org>, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, kvm@...r.kernel.org Subject: [PATCH MANUALSEL 5.15 5/8] KVM: SVM: Don't kill SEV guest if SMAP erratum triggers in usermode From: Sean Christopherson <seanjc@...gle.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@...gle.com> Reviewed-by: Liam Merwick <liam.merwick@...cle.com> Message-Id: <20220120010719.711476-10-seanjc@...gle.com> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com> Signed-off-by: Sasha Levin <sashal@...nel.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 980abc437cdaa..f05aa7290267d 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4473,7 +4473,21 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int i is_user = svm_get_cpl(vcpu) == 3; if (smap && (!smep || is_user)) { 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
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