From: ebiederm@xmission.com (Eric W. Biederman)
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
Al Viro <viro@ZenIV.linux.org.uk>,
Kees Cook <keescook@chromium.org>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
linux-s390@vger.kernel.org
Subject: Re: [PATCH 11/20] signal/s390: Use force_sigsegv in default_trap_handler
Date: Fri, 29 Oct 2021 14:32:36 -0500 [thread overview]
Message-ID: <87v91fhbjf.fsf@disp2133> (raw)
In-Reply-To: <87y26dp2hj.fsf@disp2133> (Eric W. Biederman's message of "Thu, 28 Oct 2021 10:56:24 -0500")
ebiederm@xmission.com (Eric W. Biederman) writes:
> Christian Borntraeger <borntraeger@de.ibm.com> writes:
>
>> Am 20.10.21 um 19:43 schrieb Eric W. Biederman:
>>> Reading the history it is unclear why default_trap_handler calls
>>> do_exit. It is not even menthioned in the commit where the change
>>> happened. My best guess is that because it is unknown why the
>>> exception happened it was desired to guarantee the process never
>>> returned to userspace.
>>>
>>> Using do_exit(SIGSEGV) has the problem that it will only terminate one
>>> thread of a process, leaving the process in an undefined state.
>>>
>>> Use force_sigsegv(SIGSEGV) instead which effectively has the same
>>> behavior except that is uses the ordinary signal mechanism and
>>> terminates all threads of a process and is generally well defined.
>>
>> Do I get that right, that programs can not block SIGSEGV from force_sigsegv
>> with a signal handler? Thats how I read the code. If this is true
>> then
>>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>
> 99% true, and it is what force_sigsegv(SIGSEGV) intends to do.
>
> Andy Lutormorski pointed at a race where a thread can call sigaction
> and change the signal handler after force_sigsegv has run but before
> the process dequeues the SIGSEGV.
I now have a simple patch that closes the sigaction vs force_sig race,
that I am adding to this set of changes. So now I can say programs can
not block force_sigsegv(SIGSEGV) with a signal handler or any other
method.
Eric
>>> Cc: Heiko Carstens <hca@linux.ibm.com>
>>> Cc: Vasily Gorbik <gor@linux.ibm.com>
>>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
>>> Cc: linux-s390@vger.kernel.org
>>> Fixes: ca2ab03237ec ("[PATCH] s390: core changes")
>>> History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
>>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>>> ---
>>> arch/s390/kernel/traps.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
>>> index bcefc2173de4..51729ea2cf8e 100644
>>> --- a/arch/s390/kernel/traps.c
>>> +++ b/arch/s390/kernel/traps.c
>>> @@ -84,7 +84,7 @@ static void default_trap_handler(struct pt_regs *regs)
>>> {
>>> if (user_mode(regs)) {
>>> report_user_fault(regs, SIGSEGV, 0);
>>> - do_exit(SIGSEGV);
>>> + force_sigsegv(SIGSEGV);
>>> } else
>>> die(regs, "Unknown program exception");
>>> }
>>>
next prev parent reply other threads:[~2021-10-29 19:34 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-20 17:32 [PATCH 00/20] exit cleanups Eric W. Biederman
2021-10-20 17:43 ` [PATCH 01/20] exit/doublefault: Remove apparently bogus comment about rewind_stack_do_exit Eric W. Biederman
2021-10-21 16:02 ` Kees Cook
2021-10-20 17:43 ` [PATCH 02/20] exit: Remove calls of do_exit after noreturn versions of die Eric W. Biederman
2021-10-21 16:02 ` Kees Cook
2021-10-21 16:25 ` Eric W. Biederman
2021-10-20 17:43 ` [PATCH 03/20] reboot: Remove the unreachable panic after do_exit in reboot(2) Eric W. Biederman
2021-10-21 16:05 ` Kees Cook
2021-10-20 17:43 ` [PATCH 04/20] signal/sparc32: Remove unreachable do_exit in do_sparc_fault Eric W. Biederman
2021-10-21 16:05 ` Kees Cook
2021-10-20 17:43 ` [PATCH 05/20] signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT Eric W. Biederman
2021-10-21 16:06 ` Kees Cook
2021-10-24 4:24 ` Maciej W. Rozycki
2021-10-25 20:55 ` Eric W. Biederman
2021-10-24 15:27 ` Thomas Bogendoerfer
2021-10-20 17:43 ` [PATCH 06/20] signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL) Eric W. Biederman
2021-10-20 19:57 ` Linus Torvalds
2021-10-27 14:24 ` Rich Felker
2021-10-21 16:08 ` Kees Cook
2021-10-20 17:43 ` [PATCH 07/20] signal/powerpc: On swapcontext failure force SIGSEGV Eric W. Biederman
2021-10-21 16:09 ` Kees Cook
2021-10-20 17:43 ` [PATCH 08/20] signal/sparc: In setup_tsb_params convert open coded BUG into BUG Eric W. Biederman
2021-10-21 16:12 ` Kees Cook
2021-10-20 17:43 ` [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON Eric W. Biederman
2021-10-21 16:15 ` Kees Cook
2021-11-12 15:40 ` Eric W. Biederman
2021-11-12 17:51 ` Brian Gerst
2021-11-12 19:57 ` Eric W. Biederman
2021-11-12 20:40 ` Linus Torvalds
2021-11-12 21:03 ` Eric W. Biederman
2021-11-12 21:23 ` Linus Torvalds
2021-11-12 21:24 ` Linus Torvalds
2021-11-12 21:37 ` [GIT PULL ] signal/vm86_32: Remove pointless test in BUG_ON Eric W. Biederman
2021-11-13 19:15 ` pr-tracker-bot
2021-11-12 21:43 ` [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON Eric W. Biederman
2021-10-20 17:43 ` [PATCH 10/20] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved Eric W. Biederman
2021-10-21 16:16 ` Kees Cook
2021-10-21 17:02 ` Eric W. Biederman
2021-10-21 20:33 ` Kees Cook
2021-10-21 23:08 ` Andy Lutomirski
2021-10-24 16:06 ` Eric W. Biederman
[not found] ` <875ytkygfj.fsf_-_@disp2133>
2021-10-25 21:12 ` [PATCH v2 10/32] " Linus Torvalds
2021-10-25 21:28 ` Eric W. Biederman
2021-10-25 22:25 ` Andy Lutomirski
2021-10-25 23:45 ` Linus Torvalds
2021-10-26 0:21 ` Andy Lutomirski
2021-10-20 17:43 ` [PATCH 11/20] signal/s390: Use force_sigsegv in default_trap_handler Eric W. Biederman
2021-10-21 16:17 ` Kees Cook
2021-10-26 9:38 ` Christian Borntraeger
2021-10-28 15:56 ` Eric W. Biederman
2021-10-29 19:32 ` Eric W. Biederman [this message]
2021-10-20 17:43 ` [PATCH 12/20] exit/kthread: Have kernel threads return instead of calling do_exit Eric W. Biederman
2021-10-21 11:12 ` Christoph Hellwig
2021-10-21 15:11 ` Eric W. Biederman
2021-10-21 16:21 ` Kees Cook
2021-10-20 17:43 ` [PATCH 13/20] signal: Implement force_fatal_sig Eric W. Biederman
2021-10-20 20:05 ` Linus Torvalds
2021-10-20 21:25 ` Eric W. Biederman
2021-10-25 22:41 ` Andy Lutomirski
2021-10-25 23:15 ` Linus Torvalds
2021-10-26 4:45 ` Eric W. Biederman
2021-10-26 4:57 ` Eric W. Biederman
2021-10-26 16:15 ` Linus Torvalds
2021-10-28 16:33 ` Eric W. Biederman
2021-10-21 16:24 ` Kees Cook
2021-10-21 16:33 ` Eric W. Biederman
2021-10-21 16:39 ` Kees Cook
2021-10-20 17:44 ` [PATCH 14/20] exit/syscall_user_dispatch: Send ordinary signals on failure Eric W. Biederman
2021-10-21 16:25 ` Kees Cook
2021-10-21 16:37 ` Eric W. Biederman
2021-10-21 16:40 ` Kees Cook
2021-10-21 17:05 ` Eric W. Biederman
2021-10-25 22:32 ` Andy Lutomirski
2021-10-21 16:35 ` Gabriel Krisman Bertazi
2021-10-20 17:44 ` [PATCH 15/20] signal/sparc32: Exit with a fatal signal when try_to_clear_window_buffer fails Eric W. Biederman
2021-10-21 16:34 ` Kees Cook
2021-10-21 16:56 ` Eric W. Biederman
2021-10-20 17:44 ` [PATCH 16/20] signal/sparc32: In setup_rt_frame and setup_fram use force_fatal_sig Eric W. Biederman
2021-10-21 16:34 ` Kees Cook
2021-10-20 17:44 ` [PATCH 17/20] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit Eric W. Biederman
2021-10-21 16:36 ` Kees Cook
2021-10-20 17:44 ` [PATCH 18/20] exit/rtl8723bs: Replace the macro thread_exit with a simple return 0 Eric W. Biederman
2021-10-21 7:06 ` Greg KH
2021-10-21 15:06 ` Eric W. Biederman
2021-10-21 16:37 ` Kees Cook
2021-10-20 17:44 ` [PATCH 19/20] exit/rtl8712: " Eric W. Biederman
2021-10-21 7:07 ` Greg KH
2021-10-21 16:37 ` Kees Cook
2021-10-20 17:44 ` [PATCH 20/20] exit/r8188eu: " Eric W. Biederman
2021-10-21 7:07 ` Greg KH
2021-10-21 16:37 ` Kees Cook
2021-10-20 21:51 ` [PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV) Eric W. Biederman
2021-10-21 8:09 ` Geert Uytterhoeven
2021-10-21 13:33 ` Eric W. Biederman
2021-10-21 8:32 ` Philippe Mathieu-Daudé
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