Re: [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC

From: Shakeel Butt
Date: Wed Apr 25 2018 - 18:10:51 EST

On Mon, Mar 26, 2018 at 5:27 PM, Dave Hansen
<dave.hansen@xxxxxxxxxxxxxxx> wrote:
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> I got a bug report that the following code (roughly) was
> causing a SIGSEGV:
> mprotect(ptr, size, PROT_EXEC);
> mprotect(ptr, size, PROT_NONE);
> mprotect(ptr, size, PROT_READ);
> *ptr = 100;
> The problem is hit when the mprotect(PROT_EXEC)
> is implicitly assigned a protection key to the VMA, and made
> that key ACCESS_DENY|WRITE_DENY. The PROT_NONE mprotect()
> failed to remove the protection key, and the PROT_NONE->
> PROT_READ left the PTE usable, but the pkey still in place
> and left the memory inaccessible.
> To fix this, we ensure that we always "override" the pkee
> at mprotect() if the VMA does not have execute-only
> permissions, but the VMA has the execute-only pkey.
> We had a check for PROT_READ/WRITE, but it did not work
> for PROT_NONE. This entirely removes the PROT_* checks,
> which ensures that PROT_NONE now works.
> Reported-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Fixes: 62b5f7d013f ("mm/core, x86/mm/pkeys: Add execute-only protection keys support")

Hi Dave, are you planning to send the next version of this patch or
going with this one?