From: Masami Hiramatsu <mhiramat@kernel.org>
To: zhouchengming <zhouchengming1@huawei.com>
Cc: Borislav Petkov <bp@suse.de>, <mhiramat@kernel.org>,
<ananth@linux.vnet.ibm.com>, <anil.s.keshavamurthy@intel.com>,
<davem@davemloft.net>, <hpa@zytor.com>, <tglx@linutronix.de>,
<peterz@infradead.org>, <jkosina@suse.cz>, <rostedt@goodmis.org>,
<mjurczyk@google.com>, <x86@kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kprobes, x86/alternatives: use text_mutex to protect smp_alt_modules
Date: Sat, 28 Oct 2017 17:43:10 +0900 [thread overview]
Message-ID: <20171028174310.384d62976cc5ba4859325d3a@kernel.org> (raw)
In-Reply-To: <59F334F0.2070900@huawei.com>
On Fri, 27 Oct 2017 21:30:24 +0800
zhouchengming <zhouchengming1@huawei.com> wrote:
> On 2017/10/27 20:33, Borislav Petkov wrote:
> > On Fri, Oct 27, 2017 at 07:42:45PM +0800, zhouchengming wrote:
> >> This is a real bug happened on one of our machines, below is the calltrace.
> >> We can see the trigger is at alternatives_text_reserved+0x20/0x80, and
> >> encounter a deleted (poisoned) list_head.
> > Looks like some out-of-tree, old kernel thing. We don't have
> > mlx4_stats_sysfs_create() upstream and looking at the boot timestamps,
> > it could be that register_jprobe() is not ready yet.
>
> Yes, it's an out-of-tree module, loaded when boot kernel. register_kprobe()
> maybe not ready yet, but the bug is not caused by it obviously.
>
> >
> > Looking at the Code, though:
> >
> > 20: 74 59 je 0x7b
> > 22: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
> > 29: 00 00
> > 2b:* 48 3b 71 20 cmp 0x20(%rcx),%rsi<-- trapping instruction
> > 2f: 72 3a jb 0x6b
> > 31: 48 3b 79 28 cmp 0x28(%rcx),%rdi
> > 35: 77 34 ja 0x6b
> >
> > %rcx is 0xdead0000000000d0 and that is POISON_POINTER_DELTA + 0xd0 so
> > that looks more like smp_alt_modules is not initialized yet but I could
> > could very well be wrong because this is an old kernel. So trigger that
> > with the upstream kernel without out of tree modules.
>
> The smp_alt_modules is defined by LIST_HEAD, so it's initialized at start.
>
> A deleted list_head->next = LIST_POISON1 = 0xdead000000000000 + 0x100, then
> container_of() to get the struct smp_alt_module: -0x30 = 0xdead0000000000d0
>
> Obviously, it's a deleted list_head, and I have explained clearly how it happen in
> the patch comment.
Ah, I see. It looks alternatives_text_reserved() bug at a glance.
But simply adding smp_alt mutex to alternatives_text_reserved() causes
ABBA deadlock in the kprobe's path.
So your solution is to replace the smp_alt with text_mutex, since
alternatives_text_reserved is x86 specific function.
Hmm, let me see... I agree that will be a simple way to solve, but
it also means we have 2 resources protected by text_mutex.
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2017-10-28 8:43 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-27 9:34 [PATCH] kprobes, x86/alternatives: use text_mutex to protect smp_alt_modules Zhou Chengming
2017-10-27 11:15 ` Borislav Petkov
2017-10-27 11:42 ` zhouchengming
2017-10-27 12:33 ` Borislav Petkov
2017-10-27 13:30 ` zhouchengming
2017-10-28 8:43 ` Masami Hiramatsu [this message]
2017-10-28 9:51 ` zhouchengming
2017-10-27 14:15 ` Peter Zijlstra
2017-10-28 1:26 ` zhouchengming
2017-10-28 8:44 ` Masami Hiramatsu
2017-10-30 8:03 ` Masami Hiramatsu
2017-10-31 21:59 ` Steven Rostedt
2017-11-01 1:48 ` zhouchengming
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