From: Linus Torvalds <torvalds@linux-foundation.org>
To: Kyle Huey <me@kylehuey.com>
Cc: Kees Cook <keescook@chromium.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
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>,
open list <linux-kernel@vger.kernel.org>,
linux-hardening@vger.kernel.org,
"Robert O'Callahan" <rocallahan@gmail.com>
Subject: Re: [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers
Date: Wed, 17 Nov 2021 17:11:14 -0800 [thread overview]
Message-ID: <CAHk-=wiCRbSvUi_TnQkokLeM==_+Tow0GsQXnV3UYwhsxirPwg@mail.gmail.com> (raw)
In-Reply-To: <CAP045ApYXxhiAfmn=fQM7_hD58T-yx724ctWFHO4UAWCD+QapQ@mail.gmail.com>
On Wed, Nov 17, 2021 at 4:37 PM Kyle Huey <me@kylehuey.com> wrote:
>
> This fixes most of the issues with rr, but it still changes the ptrace
> behavior for the double-SIGSEGV case
Hmm. I think that's because of how "force_sigsgv()" works.
I absolutely detest that function.
So we have signal_setup_done() doing that
if (failed)
force_sigsegv(ksig->sig);
and then force_sigsegv() has that completely insane
if (sig == SIGSEGV)
force_fatal_sig(SIGSEGV);
else
force_sig(SIGSEGV);
behavior.
And I think I know the _reason_ for that complete insanity: when
SIGSEGV takes a SIGSEGV, and there is a handler, we need to stop
trying to send more SIGSEGV's.
But it does mean that with my change, that second SIGSEGV now ends up
being that SA_IMMUTABLE kind, so yeah, it broke the debugger test -
where catching the second SIGSEGV is actually somewhat sensible (ok,
not really, but at least understandable)
End result: I think we want not a boolean, but a three-way choice for
that force_sig_info_to_task() thing:
- unconditionally fatal (for things that just want to force an exit
and used to do do_exit())
- ignore valid and unblocked handler (for that SIGSEGV recursion
case, aka force "sigdfl")
- catching signal ok
So my one-liner isn't sufficient. It wants some kind of nasty enum.
At least the enum can be entirely internal to kernel/signal.c, I
think. No need to expose this all to anything else.
Linus
next prev parent reply other threads:[~2021-11-18 1:11 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-17 18:47 [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers Kyle Huey
2021-11-17 18:51 ` Kees Cook
2021-11-17 19:05 ` Kyle Huey
2021-11-17 19:09 ` Kyle Huey
2021-11-17 21:04 ` Eric W. Biederman
2021-11-17 21:54 ` Kees Cook
2021-11-17 23:24 ` Linus Torvalds
2021-11-18 0:05 ` Kees Cook
2021-11-18 0:15 ` Linus Torvalds
2021-11-18 0:37 ` Kyle Huey
2021-11-18 1:11 ` Linus Torvalds [this message]
2021-11-18 1:20 ` Kyle Huey
2021-11-18 1:32 ` Kees Cook
2021-11-18 16:10 ` Eric W. Biederman
2021-11-19 16:07 ` Kyle Huey
2021-11-19 16:35 ` Kees Cook
2021-11-19 16:58 ` Kyle Huey
2021-11-18 21:58 ` [PATCH 0/2] SA_IMMUTABLE fixes Eric W. Biederman
2021-11-18 22:04 ` [PATCH 1/2] signal: Don't always set SA_IMMUTABLE for forced signals Eric W. Biederman
2021-11-18 23:52 ` Kees Cook
2021-11-18 23:54 ` Kees Cook
2021-11-19 15:08 ` Eric W. Biederman
2021-11-19 1:13 ` Kyle Huey
2021-11-19 15:03 ` Eric W. Biederman
2021-11-18 22:05 ` [PATCH 2/2] signal: Replace force_fatal_sig with force_exit_sig when in doubt Eric W. Biederman
2021-11-18 23:53 ` Kees Cook
2021-11-19 1:12 ` [PATCH 0/2] SA_IMMUTABLE fixes Kyle Huey
2021-11-19 15:41 ` [GIT PULL] SA_IMMUTABLE fixes for v5.16-rc2 Eric W. Biederman
2021-11-19 19:46 ` pr-tracker-bot
2021-11-17 22:29 ` [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers Kyle Huey
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