[PATCH v1 1/4] syscalls: Restore address limit after a syscall

[Andy Lutomirski]

On Wed, Mar 8, 2017 at 1:58 PM, Russell King - ARM Linux
<linux at armlinux.org.uk> wrote:
> On Wed, Mar 08, 2017 at 01:38:41PM -0800, Thomas Garnier wrote:
>> This patch prevents a syscall to modify the address limit of the
>> caller. The address limit is kept by the syscall wrapper and restored
>> just after the syscall ends.
>
> I would much rather architectures were given the opportunity to code up
> checks like this efficiently (iow, inline in the exit path assembly),
> rather than having to unconditionally call an additional function on
> every syscall, with its register saving overheads.
>

Me too.  I think the two config choices should be:

(a) BUG_ON(!segment_eq(...));

(b) No generic check at all -- arch code will handle it

--Andy