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kvm: x86: Check memopp before dereference (CVE-2016-8630)

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commit d9092f52d7 upstream.

Commit 41061cdb98 ("KVM: emulate: do not initialize memopp") removes a
check for non-NULL under incorrect assumptions. An undefined instruction
with a ModR/M byte with Mod=0 and R/M-5 (e.g. 0xc7 0x15) will attempt
to dereference a null pointer here.

Fixes: 41061cdb98
Message-Id: <1477592752-126650-2-git-send-email-osh@google.com>
Signed-off-by: Owen Hofmann <osh@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Owen Hofmann 2016-10-27 11:25:52 -07:00 committed by Greg Kroah-Hartman
parent 62fa839b8f
commit 91e1f7b0eb
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/emulate.c
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@ -5033,7 +5033,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
/* Decode and fetch the destination operand: register or memory. */
rc = decode_operand(ctxt, &ctxt->dst, (ctxt->d >> DstShift) & OpMask);
if (ctxt->rip_relative)
if (ctxt->rip_relative && likely(ctxt->memopp))
ctxt->memopp->addr.mem.ea = address_mask(ctxt,
ctxt->memopp->addr.mem.ea + ctxt->_eip);