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Re: [Qemu-devel] [PATCH] vl.c: Implement SIGILL signal handler for trigg
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From: |
Eric Blake |
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Subject: |
Re: [Qemu-devel] [PATCH] vl.c: Implement SIGILL signal handler for triggering SIGSEGV |
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Date: |
Thu, 05 Sep 2013 17:06:58 -0600 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8 |
On 09/05/2013 04:50 PM, Anthony Liguori wrote:
>> + int *p = NULL;
>> +
>> + *p = 0xDEADBEEF;
>
> I won't repeat the questions from Paolo and Lazlo (I share their
> confusion) but will simply add that you cannot rely on NULL address
> accessing causing a SEGV. Even with all the use of volatile in the
> world, there's no guarantee this is going to crash.
If you want to guarantee that a write would cause a SEGV, then you have
to use mmap(MAP_ANONYMOUS|MAP_PRIVATE) + mprotect(PROT_NONE) to get a
valid unwritable pointer that will reliably fault, rather than hoping
that NULL (or any other low-valued intptr_t cast to void*) is
sufficiently protected. But I also echo the question: why is raise()
insufficient?
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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