Re: [PATCH] Make LIST_POISON less deadly

From: Avi Kivity
Date: Tue May 20 2008 - 07:34:54 EST

Andi Kleen wrote:
Avi Kivity <avi@xxxxxxxxxxxx> 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.

No, this is the first one I see.

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.

Makes sense. I'll send out v3.

Is there a similar range on i386?

error compiling committee.c: too many arguments to function

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