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SubjectRe: [patch 05/16] mm: Allow special mappings with user access cleared
Linus Torvalds <> writes:

> On Wed, Dec 13, 2017 at 7:54 AM, Peter Zijlstra <> wrote:
>> Which is why get_user_pages() _should_ enforce this.
>> What use are protection keys if you can trivially circumvent them?
> No, we will *not* worry about protection keys in get_user_pages().
> They are not "security". They are a debug aid and safety against random mis-use.
> In particular, they are very much *NOT* about "trivially circumvent
> them". The user could just change their mapping thing, for chrissake!
> We already allow access to PROT_NONE for gdb and friends, very much on purpose.

Can you clarify this? We recently did fix read access on PROT_NONE via
gup here for ppc64

What is the expected behaviour against gup and get_user_pages for

Another issue is we end up behaving differently with PROT_NONE mapping
based on whether autonuma is enabled or not. For a PROT_NONE mapping we
return true with pte_protnone().


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