linux-kernel - [PATCH] KVM: x86: work around leak of uninitialized stack contents

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Message-Id: <20190912041817.23984-1-huangfq.daxian@gmail.com>
Date:   Thu, 12 Sep 2019 12:18:17 +0800
From:   Fuqian Huang <huangfq.daxian@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Fuqian Huang <huangfq.daxian@...il.com>
Subject: [PATCH] KVM: x86: work around leak of uninitialized stack contents

Emulation of VMPTRST can incorrectly inject a page fault
when passed an operand that points to an MMIO address.
The page fault will use uninitialized kernel stack memory
as the CR2 and error code.

The right behavior would be to abort the VM with a KVM_EXIT_INTERNAL_ERROR
exit to userspace; however, it is not an easy fix, so for now just ensure
that the error code and CR2 are zero.

Signed-off-by: Fuqian Huang <huangfq.daxian@...il.com>
---
 arch/x86/kvm/x86.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 290c3c3efb87..7f442d710858 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5312,6 +5312,7 @@ int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val,
 	/* kvm_write_guest_virt_system can pull in tons of pages. */
 	vcpu->arch.l1tf_flush_l1d = true;
 
+	memset(exception, 0, sizeof(*exception));
 	return kvm_write_guest_virt_helper(addr, val, bytes, vcpu,
 					   PFERR_WRITE_MASK, exception);
 }
-- 
2.11.0