linux-hardening - Re: [PATCH 0/2] SA

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Date:   Thu, 18 Nov 2021 17:12:23 -0800
From:   Kyle Huey <me@...ehuey.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Righi <andrea.righi@...onical.com>,
        Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        "Robert O'Callahan" <rocallahan@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Oliver Sang <oliver.sang@...el.com>, lkp@...ts.01.org,
        kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH 0/2] SA_IMMUTABLE fixes

On Thu, Nov 18, 2021 at 1:58 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
>
> 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

rr's test suite passes with both diffs applied

Tested-by: Kyle Huey <khuey@...ehuey.com>

- Kyle