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SubjectRe: [PATCH] kprobes, x86/alternatives: use text_mutex to protect smp_alt_modules
On Fri, Oct 27, 2017 at 02:33:48PM +0200, 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.
>
> 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.

Not to mention that we're about (or just have) yanked jprobes out of the
kernel entirely.

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