Messages in this thread | | | Subject | Re: [PATCH] Make LIST_POISON less deadly | From | Andi Kleen <> | Date | Tue, 20 May 2008 13:24:05 +0200 |
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Avi Kivity <avi@qumranet.com> writes:
> The list macros use LIST_POISON1 and LIST_POISON2 as undereferencable > pointers in order to trap erronous use of freed list_heads. Unfortunately > userspace can arrange for those pointers to actually be dereferencable, > potentially turning an oops to an expolit. > > To avoid this allow architectures (currently x86_64 only) to override > the default values for these pointers with truly-undereferncable values. > This is easy on x86_64 as the virtual address space is smaller than > the range spanned by pointer values.
Hmm, thought I had sent a reply earlier, but don't see it so again. My apologies if you see it twice.
The problem with your address values is that they're non canonical and will result in a #GP, not #PF and oops handler cannot display the address which will make them much less obvious.
I would rather use a guaranteed to be unmapped but canonical address like in the ffffc10000000000 - ffffc1ffffffffff range so that you still get page faults.
-Andi
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