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From: P J P <ppandit@redhat.com>
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Date: Fri, 18 Dec 2015 11:35:07 +0530
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Subject: [PATCH] i386: avoid null pointer dereference
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Hello,
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A null pointer dereference issue was reported by Mr Ling Liu, CC'd here. It
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occurs while doing I/O port write operations via hmp interface. In that,
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'current_cpu' remains null as it is not called from cpu_exec loop, which
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results in the said issue.
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Below is a proposed (tested)patch to fix this issue; Does it look okay?
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===
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From ae88a4947fab9a148cd794f8ad2d812e7f5a1d0f Mon Sep 17 00:00:00 2001
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From: Prasad J Pandit <pjp@fedoraproject.org>
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Date: Fri, 18 Dec 2015 11:16:07 +0530
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Subject: [PATCH] i386: avoid null pointer dereference
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When I/O port write operation is called from hmp interface,
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'current_cpu' remains null, as it is not called from cpu_exec()
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loop. This leads to a null pointer dereference in vapic_write
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routine. Add check to avoid it.
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Reported-by: Ling Liu <liuling-it@360.cn>
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Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
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Message-Id: <alpine.LFD.2.20.1512181129320.9805@wniryva>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: P J P <ppandit@redhat.com>
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(cherry picked from commit 4c1396cb576c9b14425558b73de1584c7a9735d7)
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---
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hw/i386/kvmvapic.c | 15 ++++++++++-----
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1 file changed, 10 insertions(+), 5 deletions(-)
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diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
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index c6d34b2..f0922da 100644
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--- a/hw/i386/kvmvapic.c
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+++ b/hw/i386/kvmvapic.c
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@@ -634,13 +634,18 @@ static int vapic_prepare(VAPICROMState *s)
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static void vapic_write(void *opaque, hwaddr addr, uint64_t data,
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unsigned int size)
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{
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- CPUState *cs = current_cpu;
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- X86CPU *cpu = X86_CPU(cs);
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- CPUX86State *env = &cpu->env;
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- hwaddr rom_paddr;
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VAPICROMState *s = opaque;
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+ X86CPU *cpu;
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+ CPUX86State *env;
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+ hwaddr rom_paddr;
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- cpu_synchronize_state(cs);
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+ if (!current_cpu) {
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+ return;
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+ }
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+
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+ cpu_synchronize_state(current_cpu);
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+ cpu = X86_CPU(current_cpu);
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+ env = &cpu->env;
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/*
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* The VAPIC supports two PIO-based hypercalls, both via port 0x7E.
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