[PATCH 0/2] SA_IMMUTABLE fixes

From: ebiederm@xmission.com (Eric W. Biederman)
To: <linux-kernel@vger.kernel.org>
Cc: Kyle Huey <me@kylehuey.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrea Righi <andrea.righi@canonical.com>,
	Shuah Khan <shuah@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Will Drewry <wad@chromium.org>,
	"open list\:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	linux-hardening@vger.kernel.org,
	Robert O'Callahan <rocallahan@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Oliver Sang <oliver.sang@intel.com>,
	lkp@lists.01.org, lkp@intel.com
Subject: [PATCH 0/2] SA_IMMUTABLE fixes
Date: Thu, 18 Nov 2021 15:58:02 -0600	[thread overview]
Message-ID: <87h7c9qg7p.fsf_-_@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <202111171728.D85A4E2571@keescook> (Kees Cook's message of "Wed, 17 Nov 2021 17:32:20 -0800")

SA_IMMUTABLE fixed issues with force_sig_seccomp and the introduction
for force_sig_fatal where the exit previously could not be interrupted
but now it can.  Unfortunately it added that behavior to all force_sig
functions under the right conditions which debuggers usage of SIG_TRAP
and debuggers handling of SIGSEGV.

Solve that by limiting SA_IMMUTABLE to just the cases that historically
debuggers have not been able to intercept.

The first patch changes force_sig_info_to_task to take a flag
that requests which behavior is desired.

The second patch adds force_exit_sig which replaces force_fatal_sig
in the cases where historically userspace would only find out about
the ``signal'' after the process has exited.

The first one with the hunk changing force_fatal_sig removed should be
suitable for backporting to v5.15. v5.15 does not implement
force_fatal_sig.

This should be enough to fix the regressions.

Kyle if you can double check me that I have properly fixed these issues
that would be appreciated.

Any other review or suggestions to improve the names would be
appreciated.  I think I have named things reasonably well but I am very
close to the code so it is easy for me to miss things.

Eric W. Biederman (2):
      signal: Don't always set SA_IMMUTABLE for forced signals
      signal: Replace force_fatal_sig with force_exit_sig when in doubt

 arch/m68k/kernel/traps.c              |  2 +-
 arch/powerpc/kernel/signal_32.c       |  2 +-
 arch/powerpc/kernel/signal_64.c       |  4 ++--
 arch/s390/kernel/traps.c              |  2 +-
 arch/sparc/kernel/signal_32.c         |  4 ++--
 arch/sparc/kernel/windows.c           |  2 +-
 arch/x86/entry/vsyscall/vsyscall_64.c |  2 +-
 arch/x86/kernel/vm86_32.c             |  2 +-
 include/linux/sched/signal.h          |  1 +
 kernel/entry/syscall_user_dispatch.c  |  4 ++--
 kernel/signal.c                       | 36 ++++++++++++++++++++++++++++-------
 11 files changed, 42 insertions(+), 19 deletions(-)

Eric