On 09/03/16 03:02, Petr Mladek wrote:
> On Tue 2016-03-08 18:33:57, Balbir Singh wrote:
>> Changelog v5:
>> 1. Removed the mini-stack frame created for klp_return_helper.
>> As a result of the mini-stack frame, function with > 8
>> arguments could not be patched
>> 2. Removed camel casing in the comments
> I tested this patch and it fails when I call a patched printk()
> from a module.
>
> You might try it with the test patch below. It is a bit twisted
> because it calls the patched printk from livepatch_cmdline_proc_show()
> that it added by the same patch module. Please, look at
> livepatch_cmdline_proc_show(), it does:
>
> static int count;
>
> if (!count++)
> trace_printk("%s\n", "this has been live patched");
> else
> printk("%s\n", "this has been live patched");
>
>
> It means that calls only trace_printk() when called first time.
> It calls the patched printk when called second time.
>
>
> I have tested it the following way:
>
>
> # booted kernel with the changes below
> # applied the patch:
> $> modprobe livepatch-sample
>
> # trigger the pached printk()
> $>cat /sys/kernel/livepatch/livepatch_sample/enabled
> 1
>
> # look into both dmesg and trace buffer
> $> dmesg | tail -n 1
> [ 727.537307] patch enabled: 1
> $> cat /sys/kernel/debug/tracing/trace | tail -n 1
> cat-3588 [003] .... 727.537448: livepatch_printk: patch enabled: 1
>
> # trigger livepatch_cmdline_proc_show() 1st time
> c79:~ # cat /proc/cmdline
> this has been live patched
>
> # the message appeared only in trace buffer
> $> dmesg | tail -n 1
> [ 727.537307] patch enabled: 1
> c79:~ # cat /sys/kernel/debug/tracing/trace | tail -n 1
> cat-3511 [000] .... 862.958383: livepatch_cmdline_proc_show: this has been live patched
>
>
> # trigger livepatch_cmdline_proc_show() 2nd time
> c79:~ # cat /proc/cmdline
>
> !!! KABOOM !!!
>
> It is becaused it tried to call the patched printk()?
>
Yes, the situation is that we restored the r2 for the kernel (from ftrace_caller, it is now kernel_toc),
whereas the LR points to the module. The difference between r2 and r0 > 4GB.
Very good test case. Did it work with v4? I presume it did because we have enough space to save both
Thanks,
Balbir Singh
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