Commit 49a1431d authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Bug the VM if the emulator generates a bogus exception vector 



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: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220526210817.3428868-8-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 1cca2f8c

arch/x86/kvm/emulate.c

+5 −2
Original line number Diff line number Diff line
@@ -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)