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    SubjectRe: [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC
    On Wed, 25 Apr 2018, Shakeel Butt wrote:
    > On Mon, Mar 26, 2018 at 5:27 PM, Dave Hansen
    > <dave.hansen@linux.intel.com> wrote:
    > >
    > > From: Dave Hansen <dave.hansen@linux.intel.com>
    > >
    > > 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@google.com>
    > >
    > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    > > 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?

    Right, some enlightment would be appreciated. I'm lost in the dozen
    different threads discussing this back and forth.

    Thanks,

    tglx

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