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From: Kyle Huey <me@kylehuey.com>
To: Kees Cook <keescook@chromium.org>
Cc: "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@vger.kernel.org, open list <linux-kernel@vger.kernel.org>,
	linux-hardening@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Robert O'Callahan" <rocallahan@gmail.com>
Subject: Re: [REGRESSION] 5.16rc1: SA_IMMUTABLE breaks debuggers
Date: Wed, 17 Nov 2021 11:05:51 -0800	[thread overview]
Message-ID: <CAP045Apg9AUZN_WwDd6AwxovGjCA++mSfzrWq-mZ7kXYS+GCfA@mail.gmail.com> (raw)
In-Reply-To: <202111171049.3F9C5F1@keescook>

On Wed, Nov 17, 2021 at 10:51 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Nov 17, 2021 at 10:47:13AM -0800, Kyle Huey wrote:
> > rr, a userspace record and replay debugger[0], is completely broken on
> > 5.16rc1. I bisected this to 00b06da29cf9dc633cdba87acd3f57f4df3fd5c7.
> >
> > That patch makes two changes, it blocks sigaction from changing signal
> > handlers once the kernel has decided to force the program to take a
> > signal and it also stops notifying ptracers of the signal in the same
> > circumstances. The latter behavior is just wrong. There's no reason
> > that ptrace should not be able to observe and even change
> > (non-SIGKILL) forced signals.  It should be reverted.
> >
> > This behavior change is also observable in gdb. If you take a program
> > that sets SIGSYS to SIG_IGN and then raises a SIGSYS via
> > SECCOMP_RET_TRAP and run it under gdb on a good kernel gdb will stop
> > when the SIGSYS is raised, let you inspect program state, etc. After
> > the SA_IMMUTABLE change gdb won't stop until the program has already
> > died of SIGSYS.
>
> Ah, hm, this was trying to fix the case where a program trips
> SECCOMP_RET_KILL (which is a "fatal SIGSYS"), and had been unobservable
> before. I guess the fix was too broad...

Perhaps I don't understand precisely what you mean by this, but gdb's
behavior for a program that is SECCOMP_RET_KILLed was not changed by
this patch (the SIGSYS is not observed until after program exit before
or after this change).

- Kyle

  reply	other threads:[~2021-11-17 19:06 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-17 18:47 Kyle Huey
2021-11-17 18:51 ` Kees Cook
2021-11-17 19:05   ` Kyle Huey [this message]
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
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
2021-11-18  5:43 ` Thorsten Leemhuis
2021-11-20  6:13   ` Thorsten Leemhuis

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