From 4c1396cb576c9b14425558b73de1584c7a9735d7 Mon Sep 17 00:00:00 2001 From: P J P Date: Fri, 18 Dec 2015 11:35:07 +0530 Subject: [PATCH] i386: avoid null pointer dereference Hello, A null pointer dereference issue was reported by Mr Ling Liu, CC'd here. It occurs while doing I/O port write operations via hmp interface. In that, 'current_cpu' remains null as it is not called from cpu_exec loop, which results in the said issue. Below is a proposed (tested)patch to fix this issue; Does it look okay? === From ae88a4947fab9a148cd794f8ad2d812e7f5a1d0f Mon Sep 17 00:00:00 2001 From: Prasad J Pandit Date: Fri, 18 Dec 2015 11:16:07 +0530 Subject: [PATCH] i386: avoid null pointer dereference When I/O port write operation is called from hmp interface, 'current_cpu' remains null, as it is not called from cpu_exec() loop. This leads to a null pointer dereference in vapic_write routine. Add check to avoid it. Reported-by: Ling Liu Signed-off-by: Prasad J Pandit Message-Id: Signed-off-by: Paolo Bonzini Signed-off-by: P J P --- hw/i386/kvmvapic.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c index c6d34b2..f0922da 100644 --- a/hw/i386/kvmvapic.c +++ b/hw/i386/kvmvapic.c @@ -634,13 +634,18 @@ static int vapic_prepare(VAPICROMState *s) static void vapic_write(void *opaque, hwaddr addr, uint64_t data, unsigned int size) { - CPUState *cs = current_cpu; - X86CPU *cpu = X86_CPU(cs); - CPUX86State *env = &cpu->env; - hwaddr rom_paddr; VAPICROMState *s = opaque; + X86CPU *cpu; + CPUX86State *env; + hwaddr rom_paddr; - cpu_synchronize_state(cs); + if (!current_cpu) { + return; + } + + cpu_synchronize_state(current_cpu); + cpu = X86_CPU(current_cpu); + env = &cpu->env; /* * The VAPIC supports two PIO-based hypercalls, both via port 0x7E. -- 2.7.4