linux-kernel - [PATCH] KVM: x86: remove bogus user-triggerable WARN

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Date:   Thu, 19 Mar 2020 13:43:18 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     syzbot+00be5da1d75f1cc95f6b@...kaller.appspotmail.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [PATCH] KVM: x86: remove bogus user-triggerable WARN_ON

The WARN_ON is essentially comparing a user-provided value with 0.  It is
trivial to trigger it just by passing garbage to KVM_SET_CLOCK.  Guests
can break if you do so, but if it hurts when you do like this just do not
do it.

Reported-by: syzbot+00be5da1d75f1cc95f6b@...kaller.appspotmail.com
Fixes: 9446e6fce0ab ("KVM: x86: fix WARN_ON check of an unsigned less than zero")
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3156e25b0774..d65ff2008cf1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2444,7 +2444,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 	vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
 	vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
 	vcpu->last_guest_tsc = tsc_timestamp;
-	WARN_ON((s64)vcpu->hv_clock.system_time < 0);
 
 	/* If the host uses TSC clocksource, then it is stable */
 	pvclock_flags = 0;
-- 
2.18.2