On Wed, Feb 08, 2017 at 02:58:28PM -0700, Scott Bauer wrote:
> On Wed, Feb 08, 2017 at 10:15:28PM +0100, Arnd Bergmann wrote:
> > When CONFIG_KASAN is in use, the sed_ioctl function uses unusually large
> > stack,
> > as each possible ioctl argument gets its own stack area plus redzone:
> >
> > block/sed-opal.c: In function 'sed_ioctl':
> > block/sed-opal.c:2447:1: error: the frame size of 2256 bytes is larger than
> > 2048 bytes [-Werror=frame-larger-than=]
> >
> > Moving the copy_from_user() calls into the individual functions has little
> > effect on readablility, but significantly reduces the stack size, with the
> > largest individual function (opal_enable_disable_shadow_mbr) now at
> > reasonable 456 bytes.
> >
> > Fixes: 455a7b238cd6 ("block: Add Sed-opal library")
> > Signed-off-by: Arnd Bergmann <[email protected]>
>
>
> Hi Arnd,
>
> Thank you for the report. We want to keep the function calls agnostic to
> userland.
> In the future we will have in-kernel callers and I don't want to have to do
> any
> get_fs(KERNEL_DS) wizardry.
>
> Instead I think we can use a union to lessen the stack burden. I tested this
> patch just now
> with config_ksasan and was able to build.
Nack on this patch, it only really masks the issue. Keith pointed out we have a
call chain
up to this ioctl then deeper down into nvme then the block layer. If we use 25%
of the stack
just for this function it's still too dangerous and we'll run into corruption
later on and not
remember this fix. I'll come up with another solution.
