Re: [PATCH] Make LIST_POISON less deadly

[Avi Kivity <avi@qumranet.com>]

Andi Kleen wrote:
> 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.
>   

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