x86: signal: don't do sas_ss_reset() until we are certain that sigframe won't be...
authorAl Viro <viro@zeniv.linux.org.uk>
Thu, 1 Jul 2021 01:56:43 +0000 (18:56 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 1 Jul 2021 18:06:06 +0000 (11:06 -0700)
commit97c885d585c53d3f1ad4545b0ee10f0bdfaa1a4d
tree7cde905a1c673d67360873c93eb017078382af09
parentc3eb84092b326a353725edcc8274a3782f1d1524
x86: signal: don't do sas_ss_reset() until we are certain that sigframe won't be abandoned

Currently we handle SS_AUTODISARM as soon as we have stored the altstack
settings into sigframe - that's the point when we have set the things up
for eventual sigreturn to restore the old settings.  And if we manage to
set the sigframe up (we are not done with that yet), everything's fine.
However, in case of failure we end up with sigframe-to-be abandoned and
SIGSEGV force-delivered.  And in that case we end up with inconsistent
rules - late failures have altstack reset, early ones do not.

It's trivial to get consistent behaviour - just handle SS_AUTODISARM once
we have set the sigframe up and are committed to entering the handler,
i.e.  in signal_delivered().

Link: https://lore.kernel.org/lkml/20200404170604.GN23230@ZenIV.linux.org.uk/
Link: https://github.com/ClangBuiltLinux/linux/issues/876
Link: https://lkml.kernel.org/r/20210422230846.1756380-1-ndesaulniers@google.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
include/linux/compat.h
include/linux/signal.h
kernel/signal.c