x86/pkeys: Override pkey when moving away from PROT_EXEC

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 <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Michael Ellermen <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ram Pai <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Fixes: 62b5f7d013f ("mm/core, x86/mm/pkeys: Add execute-only protection keys support")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions