linux-kernel - Re: [PATCH] kprobes, x86/alternatives: use text_mutex to protect smp_alt

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Message-ID: <20171027123348.GE1305@nazgul.tnic>
Date:   Fri, 27 Oct 2017 14:33:48 +0200
From:   Borislav Petkov <bp@...e.de>
To:     zhouchengming <zhouchengming1@...wei.com>
Cc:     mhiramat@...nel.org, ananth@...ux.vnet.ibm.com,
        anil.s.keshavamurthy@...el.com, davem@...emloft.net, hpa@...or.com,
        tglx@...utronix.de, peterz@...radead.org, jkosina@...e.cz,
        rostedt@...dmis.org, mjurczyk@...gle.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes, x86/alternatives: use text_mutex to protect
 smp_alt_modules

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.

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.

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--