[0/2] Don't use SIGMINSTKSZ when enforcing alternative signal stack size for compat tasks

Message

Will Deacon July 25, 2018, 1:45 p.m. UTC

Hi all,

The Debian folks have observed a failure in the 32-bit arm glibc testsuite
when running under a 64-bit kernel. They tracked this down to sigaltstack(2)
enforcing the alternative signal stack to be at least SIGMINSTKSZ bytes,
which is higher for native arm64 tasks than compat 32-bit tasks.

These patches resolve the issue by allowing an architecture to define
COMPAT_SIGMINSTKSZ for compat tasks, which is then used by the sigaltstack
checking code.

Feedback welcome,

Will

--->8

Will Deacon (2):
  signal: Introduce COMPAT_SIGMINSTKSZ for use in compat_sys_sigaltstack
  arm64: compat: Provide definition for COMPAT_SIGMINSTKSZ

 arch/arm64/include/asm/compat.h |  1 +
 include/linux/compat.h          |  3 +++
 kernel/signal.c                 | 14 +++++++++-----
 3 files changed, 13 insertions(+), 5 deletions(-)

Comments

Aurelien Jarno July 29, 2019, 8:23 p.m. UTC | #1

On 2018-07-25 14:45, Will Deacon wrote:
> Hi all,
> 
> The Debian folks have observed a failure in the 32-bit arm glibc testsuite
> when running under a 64-bit kernel. They tracked this down to sigaltstack(2)
> enforcing the alternative signal stack to be at least SIGMINSTKSZ bytes,
> which is higher for native arm64 tasks than compat 32-bit tasks.
> 
> These patches resolve the issue by allowing an architecture to define
> COMPAT_SIGMINSTKSZ for compat tasks, which is then used by the sigaltstack
> checking code.
> 
> Feedback welcome,
> 
> Will
> 
> --->8
> 
> Will Deacon (2):
>   signal: Introduce COMPAT_SIGMINSTKSZ for use in compat_sys_sigaltstack
>   arm64: compat: Provide definition for COMPAT_SIGMINSTKSZ

Only the first patch went to the stable kernels. The second one is
missing, so the bug is still not fixed in those kernels. Would it be
possible to also get it included?

Thanks,
Aurelien

Will Deacon July 30, 2019, 9:27 a.m. UTC | #2

On Mon, Jul 29, 2019 at 10:23:02PM +0200, Aurelien Jarno wrote:
> On 2018-07-25 14:45, Will Deacon wrote:
> > Hi all,
> > 
> > The Debian folks have observed a failure in the 32-bit arm glibc testsuite
> > when running under a 64-bit kernel. They tracked this down to sigaltstack(2)
> > enforcing the alternative signal stack to be at least SIGMINSTKSZ bytes,
> > which is higher for native arm64 tasks than compat 32-bit tasks.
> > 
> > These patches resolve the issue by allowing an architecture to define
> > COMPAT_SIGMINSTKSZ for compat tasks, which is then used by the sigaltstack
> > checking code.
> > 
> > Feedback welcome,
> > 
> > Will
> > 
> > --->8
> > 
> > Will Deacon (2):
> >   signal: Introduce COMPAT_SIGMINSTKSZ for use in compat_sys_sigaltstack
> >   arm64: compat: Provide definition for COMPAT_SIGMINSTKSZ
> 
> Only the first patch went to the stable kernels. The second one is
> missing, so the bug is still not fixed in those kernels. Would it be
> possible to also get it included?

Damn, you're right. I think the autosel bot picked the first commit but not
the second. In hindsight, we should've tagged them both, but oh well. I've
posted the patch here for -stable, with you on cc:

https://lore.kernel.org/lkml/[e-mail]/T/#u

Will