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From: Dave Martin <Dave.Martin@arm.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	James Morse <James.Morse@arm.com>,
	Will Deacon <Will.Deacon@arm.com>
Subject: Re: [REVIEW][PATCH 03/26] signal/arm64: Use force_sig not force_sig_fault for SIGKILL
Date: Thu, 23 May 2019 11:21:04 +0100	[thread overview]
Message-ID: <20190523102101.GW28398@e103592.cambridge.arm.com> (raw)
In-Reply-To: <20190523003916.20726-4-ebiederm@xmission.com>

On Thu, May 23, 2019 at 01:38:53AM +0100, Eric W. Biederman wrote:
> It really only matters to debuggers but the SIGKILL does not have any
> si_codes that use the fault member of the siginfo union.  Correct this
> the simple way and call force_sig instead of force_sig_fault when the
> signal is SIGKILL.

I haven't fully understood the context for this, but why does it matter
what's in siginfo for SIGKILL?  My understanding is that userspace
(including ptrace) never gets to see it anyway for the SIGKILL case.

Here it feels like SIGKILL is logically a synchronous, thread-targeted
fault: we must ensure that no subsequent insn in current executes (just
like other fault signal).  In this case, I thought we fall back to
SIGKILL not because there is no fault, but because we failed to
properly diagnose or report the type of fault that occurred.

So maybe handling it consistently with other faults signals makes
sense.  The fact that delivery of this signal destroys the process
before anyone can look at the resulting siginfo feels like a
side-effect rather than something obviously wrong.

The siginfo is potentially useful diagnostic information, that we could
subsequently provide a means to access post-mortem.

I just dived in on this single patch, so I may be missing something more
fundamental, or just being pedantic...

Cheers
---Dave

> Cc: stable@vger.kernel.org
> Cc: Dave Martin <Dave.Martin@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Fixes: af40ff687bc9 ("arm64: signal: Ensure si_code is valid for all fault signals")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>  arch/arm64/kernel/traps.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index ade32046f3fe..0feb17bdcaa0 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -282,6 +282,11 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
>  		current->thread.fault_address = 0;
>  		current->thread.fault_code = err;
>  
> +		if (signo == SIGKILL) {
> +			arm64_show_signal(signo, str);
> +			force_sig(signo, current);
> +			return;
> +		}
>  		arm64_force_sig_fault(signo, sicode, addr, str);
>  	} else {
>  		die(str, regs, err);
> -- 
> 2.21.0
> 

  parent reply	other threads:[~2019-05-23 10:21 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-23  0:38 [REVIEW][PATCH 00/26] signal: Remove task argument from force_sig_info Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 01/26] signal: Correct namespace fixups of si_pid and si_uid Eric W. Biederman
     [not found]   ` <20190529131503.F2AC221871@mail.kernel.org>
2019-05-29 15:18     ` Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 02/26] signal/ptrace: Simplify and fix PTRACE_KILL Eric W. Biederman
2019-05-29 14:35   ` Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 03/26] signal/arm64: Use force_sig not force_sig_fault for SIGKILL Eric W. Biederman
2019-05-23 10:17   ` Will Deacon
2019-05-23 14:59     ` Eric W. Biederman
2019-05-23 16:11     ` [REVIEW][PATCHv2 " Eric W. Biederman
2019-05-23 16:15       ` Will Deacon
2019-05-23 20:59         ` Eric W. Biederman
2019-05-24 10:00           ` Will Deacon
2019-05-24 22:36             ` Eric W. Biederman
2019-05-29 15:12               ` Will Deacon
2019-05-29 15:34                 ` Eric W. Biederman
2019-05-23 10:21   ` Dave Martin [this message]
2019-05-23 14:53     ` [REVIEW][PATCH " Eric W. Biederman
2019-05-23 16:12       ` Dave P Martin
2019-05-23 21:00         ` Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 04/26] signal/drbd: Use send_sig not force_sig Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 05/26] signal/bpfilter: Fix bpfilter_kernl to use " Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 06/26] signal/pid_namespace: Fix reboot_pid_ns " Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 07/26] signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 08/26] signal: Remove task parameter from force_sigsegv Eric W. Biederman
2019-05-23  0:38 ` [REVIEW][PATCH 09/26] signal: Remove task parameter from force_sig Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 10/26] signal: Remove task parameter from force_sig_mceerr Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 11/26] signal/x86: Remove task parameter from send_sigtrap Eric W. Biederman
2019-05-28 18:18   ` Thomas Gleixner
2019-05-23  0:39 ` [REVIEW][PATCH 12/26] signal/um: " Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 13/26] signal/sh: Remove tsk parameter from force_sig_info_fault Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 14/26] signal/riscv: Remove tsk parameter from do_trap Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 15/26] signal/nds32: Remove tsk parameter from send_sigtrap Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 16/26] signal/arm: Remove tsk parameter from ptrace_break Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 17/26] signal/arm: Remove tsk parameter from __do_user_fault Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 18/26] signal/unicore32: " Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 19/26] signal: Explicitly call force_sig_fault on current Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 20/26] signal: Use force_sig_fault_to_task for the two calls that don't deliver to current Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 21/26] signal: Remove the task parameter from force_sig_fault Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 22/26] signal: Properly set TRACE_SIGNAL_LOSE_INFO in __send_signal Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 23/26] signal: Move the computation of force into send_signal and correct it Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 24/26] signal: Generate the siginfo in force_sig Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 25/26] signal: Factor force_sig_info_to_task out of force_sig_info Eric W. Biederman
2019-05-23  0:39 ` [REVIEW][PATCH 26/26] signal: Remove the signal number and task parameters from force_sig_info Eric W. Biederman
2019-05-24 23:35 ` [REVIEW][PATCH 00/26] signal: Remove task argument " Eric W. Biederman
2019-05-29 15:37 ` Eric W. Biederman

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