Messages in this thread | | | Date | Sat, 28 Oct 2017 09:26:56 +0800 | From | zhouchengming <> | Subject | Re: [PATCH] kprobes, x86/alternatives: use text_mutex to protect smp_alt_modules |
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On 2017/10/27 22:15, Peter Zijlstra wrote: > 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.
Well... but this is a bug of alternatives_text_reserved(), it traverse the list without holding the smp_alt mutex. So all users of it, like kprobes, will still have this problem. Maybe I could think of a way to get rid of the mutex entirely.
Thanks.
> . >
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