Re: [PATCH v2 1/2] sched: move stack_canary field at the top of task_struct

Christophe LEROY [off-list ref] writes:

Le 19/09/2018 =C3=A0 13:58, Peter Zijlstra a =C3=A9crit=C2=A0:

quoted

On Wed, Sep 19, 2018 at 11:14:43AM +0000, Christophe Leroy wrote:

quoted

In order to allow the use of non global stack protector canary,
the stack canary needs to be located at a know offset defined
in Makefile via -mstack-protector-guard-offset.

On powerpc/32, register r2 points to current task_struct at
all time, the stack_canary located inside task_struct can be
used directly if it is located in a known place.

In order to allow that, this patch moves the stack_canary field
out of the randomized area of task_struct.

=20
And you cannot use something like asm-offsets to extract this?

I have not been able to find a way to define the compilation flags AFTER=

=20

building asm-offsets.h, see https://patchwork.ozlabs.org/patch/971521/

If you have a suggestion, it is welcomed.

Hmm, that's something of a hard problem.

But the stack canary is one of the things we really *do* want to be
randomised, so we should probably try to come up with a solution.

cheers