From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Kees Cook <keescook@chromium.org>,
Robert Dinse <nanook@eskimo.com>
Subject: [PATCH v2 7/8] KVM: x86: Bug the VM if the emulator generates a bogus exception vector
Date: Thu, 26 May 2022 21:08:16 +0000 [thread overview]
Message-ID: <20220526210817.3428868-8-seanjc@google.com> (raw)
In-Reply-To: <20220526210817.3428868-1-seanjc@google.com>
Bug the VM if KVM's emulator attempts to inject a bogus exception vector.
The guest is likely doomed even if KVM continues on, and propagating a
bad vector to the rest of KVM runs the risk of breaking other assumptions
in KVM and thus triggering a more egregious bug.
All existing users of emulate_exception() have hardcoded vector numbers
(__load_segment_descriptor() uses a few different vectors, but they're
all hardcoded), and future users are likely to follow suit, i.e. the
change to emulate_exception() is a glorified nop.
As for the ctxt->exception.vector check in x86_emulate_insn(), the few
known times the WARN has been triggered in the past is when the field was
not set when synthesizing a fault, i.e. for all intents and purposes the
check protects against consumption of uninitialized data.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/emulate.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 70a8e0cd9fdc..2aa17462a9ac 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -624,7 +624,9 @@ static unsigned long seg_base(struct x86_emulate_ctxt *ctxt, int seg)
static int emulate_exception(struct x86_emulate_ctxt *ctxt, int vec,
u32 error, bool valid)
{
- WARN_ON(vec > 0x1f);
+ if (KVM_EMULATOR_BUG_ON(vec > 0x1f, ctxt))
+ return X86EMUL_UNHANDLEABLE;
+
ctxt->exception.vector = vec;
ctxt->exception.error_code = error;
ctxt->exception.error_code_valid = valid;
@@ -5728,7 +5730,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
done:
if (rc == X86EMUL_PROPAGATE_FAULT) {
- WARN_ON(ctxt->exception.vector > 0x1f);
+ if (KVM_EMULATOR_BUG_ON(ctxt->exception.vector > 0x1f, ctxt))
+ return EMULATION_FAILED;
ctxt->have_exception = true;
}
if (rc == X86EMUL_INTERCEPTED)
--
2.36.1.255.ge46751e96f-goog
next prev parent reply other threads:[~2022-05-26 21:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-26 21:08 [PATCH v2 0/8] KVM: x86: Emulator _regs fixes and cleanups Sean Christopherson
2022-05-26 21:08 ` [PATCH v2 1/8] KVM: x86: Grab regs_dirty in local 'unsigned long' Sean Christopherson
2022-05-26 21:08 ` [PATCH v2 2/8] KVM: x86: Harden _regs accesses to guard against buggy input Sean Christopherson
2022-05-26 21:08 ` [PATCH v2 3/8] KVM: x86: Omit VCPU_REGS_RIP from emulator's _regs array Sean Christopherson
2022-05-31 18:04 ` Kees Cook
2022-05-26 21:08 ` [PATCH v2 4/8] KVM: x86: Use 16-bit fields to track dirty/valid emulator GPRs Sean Christopherson
2022-05-26 21:08 ` [PATCH v2 5/8] KVM: x86: Reduce the number of emulator GPRs to '8' for 32-bit KVM Sean Christopherson
2022-05-31 18:04 ` Kees Cook
2022-05-26 21:08 ` [PATCH v2 6/8] KVM: x86: Bug the VM if the emulator accesses a non-existent GPR Sean Christopherson
2022-05-31 18:06 ` Kees Cook
2022-06-01 8:29 ` Vitaly Kuznetsov
2022-06-02 16:01 ` Sean Christopherson
2022-05-26 21:08 ` Sean Christopherson [this message]
2022-05-31 18:06 ` [PATCH v2 7/8] KVM: x86: Bug the VM if the emulator generates a bogus exception vector Kees Cook
2022-06-01 8:31 ` Vitaly Kuznetsov
2022-05-26 21:08 ` [PATCH v2 8/8] KVM: x86: Bug the VM on an out-of-bounds data read Sean Christopherson
2022-05-31 18:06 ` Kees Cook
2022-06-01 8:39 ` Vitaly Kuznetsov
2022-05-26 23:14 ` [PATCH v2 0/8] KVM: x86: Emulator _regs fixes and cleanups Robert Dinse
2022-06-08 12:23 ` Paolo Bonzini
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