Re: [PATCH 1/2] x86, pkeys: check against max pkey to avoid overflows

On Thu, Feb 23, 2017 at 02:26:03PM -0800, Dave Hansen wrote:

From: Dave Hansen <dave.hansen@linux.intel.com>

Kirill got a warning from UBSAN about undefined behavior when using
protection keys.  He is running on hardware that actually has support
for it, which is not widely available.

The warning was because we did some very large shifts of integers when
doing a pkey_free() of a large, invalid value because we never check
that the pkey "fits" into the mm_pkey_allocation_map().

I do not believe there is any danger here of anything bad happening
other than some aliasing issues where somebody could do:

	pkey_free(35);

and the kernel would effectively execute:

	pkey_free(8);

While this might be confusing to an app that was doing something
stupid, it has to do something stupid and the effects are limited to
the app shooting itself in the foot.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

Acked-by: Kirill A. Shutemov <redacted>

-- 
 Kirill A. Shutemov