Re: [Adeos-main] [PATCH] ipipe: Prevent unwritable pages after mprotect

[Jan Kiszka <jan.kiszka@domain.hid>]

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On 2011-07-08 13:55, Gilles Chanteperdrix wrote:
> On 07/07/2011 09:14 PM, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@domain.hid>
>>
>> Page protection changes issued via mprotect, e.g. to enable executable
>> stacks, cause spurious minor faults as they remove the write permission
>> from the modified range again. Avoid this by faking shared pages so that
>> vm_get_page_prot returns the desired page permissions.
> 
> This looks dangerous to me. Have you checked that write to private heaps
> will not end up corrupting shared data?

Can't follow this yet.

If you check the comment on protection_map in mm/mmap.c, the difference
between private and shared is in real write vs. COW-able write. That's
what my patch is exploiting to get the proper arch-dependent page
protection bits.

Are you aware of side effects or do you know a better way to inject
write permissions into the protection flags?

Jan


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