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KVM: SVM: Don't kill SEV guest if SMAP erratum triggers in usermode 

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>
This commit is contained in:
Sean Christopherson 2022-01-20 01:07:19 +00:00 committed by Paolo Bonzini
parent 3280cc22ae
commit cdf85e0c5d
1 changed files with 15 additions and 1 deletions
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16
arch/x86/kvm/svm/svm.c
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@ -4360,7 +4360,21 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
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);
}
resume_guest: