From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>, Feng Tang <feng.tang@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
contact@xogium.me, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, Russell King <linux@armlinux.org.uk>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] panic: Ensure preemption is disabled during panic()
Date: Wed, 2 Oct 2019 13:58:46 -0700 [thread overview]
Message-ID: <201910021355.E578D2FFAF@keescook> (raw)
In-Reply-To: <20191002123538.22609-1-will@kernel.org>
On Wed, Oct 02, 2019 at 01:35:38PM +0100, Will Deacon wrote:
> Calling 'panic()' on a kernel with CONFIG_PREEMPT=y can leave the
> calling CPU in an infinite loop, but with interrupts and preemption
> enabled. From this state, userspace can continue to be scheduled,
> despite the system being "dead" as far as the kernel is concerned. This
> is easily reproducible on arm64 when booting with "nosmp" on the command
> line; a couple of shell scripts print out a periodic "Ping" message
> whilst another triggers a crash by writing to /proc/sysrq-trigger:
>
> | sysrq: Trigger a crash
> | Kernel panic - not syncing: sysrq triggered crash
> | CPU: 0 PID: 1 Comm: init Not tainted 5.2.15 #1
> | Hardware name: linux,dummy-virt (DT)
> | Call trace:
> | dump_backtrace+0x0/0x148
> | show_stack+0x14/0x20
> | dump_stack+0xa0/0xc4
> | panic+0x140/0x32c
> | sysrq_handle_reboot+0x0/0x20
> | __handle_sysrq+0x124/0x190
> | write_sysrq_trigger+0x64/0x88
> | proc_reg_write+0x60/0xa8
> | __vfs_write+0x18/0x40
> | vfs_write+0xa4/0x1b8
> | ksys_write+0x64/0xf0
> | __arm64_sys_write+0x14/0x20
> | el0_svc_common.constprop.0+0xb0/0x168
> | el0_svc_handler+0x28/0x78
> | el0_svc+0x8/0xc
> | Kernel Offset: disabled
> | CPU features: 0x0002,24002004
> | Memory Limit: none
> | ---[ end Kernel panic - not syncing: sysrq triggered crash ]---
> | Ping 2!
> | Ping 1!
> | Ping 1!
> | Ping 2!
>
> The issue can also be triggered on x86 kernels if CONFIG_SMP=n, otherwise
> local interrupts are disabled in 'smp_send_stop()'.
>
> Disable preemption in 'panic()' before re-enabling interrupts.
Is this perhaps the correct solution for what commit c39ea0b9dd24 ("panic:
avoid the extra noise dmesg") was trying to fix?
Either way:
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: <stable@vger.kernel.org>
> Link: https://lore.kernel.org/r/BX1W47JXPMR8.58IYW53H6M5N@dragonstone
> Reported-by: Xogium <contact@xogium.me>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
> kernel/panic.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 47e8ebccc22b..f470a038b05b 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -180,6 +180,7 @@ void panic(const char *fmt, ...)
> * after setting panic_cpu) from invoking panic() again.
> */
> local_irq_disable();
> + preempt_disable_notrace();
>
> /*
> * It's possible to come here directly from a panic-assertion and
> --
> 2.23.0.444.g18eeb5a265-goog
>
--
Kees Cook
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-10-02 20:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-02 12:35 [PATCH] panic: Ensure preemption is disabled during panic() Will Deacon
2019-10-02 20:58 ` Kees Cook [this message]
2019-10-03 20:56 ` Will Deacon
2019-10-04 9:11 ` Petr Mladek
2019-10-04 9:29 ` Russell King - ARM Linux admin
2019-10-04 10:49 ` Will Deacon
2019-10-04 11:15 ` Petr Mladek
2019-10-04 13:51 ` Feng Tang
2019-10-07 8:02 ` Jiri Kosina
2019-10-02 21:45 ` Andrew Morton
2019-10-03 20:53 ` Will Deacon
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