linux-kernel - [PATCH v2 7/8] KVM: x86: Bug the VM if the emulator generates a bogus exception vector

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20220526210817.3428868-8-seanjc@google.com>
Date:   Thu, 26 May 2022 21:08:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Robert Dinse <nanook@...imo.com>
Subject: [PATCH v2 7/8] 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: Sean Christopherson <seanjc@...gle.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