Re: [PATCH] ARM: ftrace: Only set kernel memory back to read-only after boot

[Stefan Agner <stefan@agner.ch>]

On 21.06.2018 18:50, Steven Rostedt wrote:
> On Thu, 21 Jun 2018 12:47:10 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
>> From: Steven Rostedt (VMware) <rostedt@goodmis.org>
>>
>> Dynamic ftrace requires modifying the code segments that are usually
>> set to read-only. To do this, a per arch function is called both before
>> and after the ftrace modifications are performed. The "before" function
>> will set kernel code text to read-write to allow for ftrace to make the
>> modifications, and the "after" function will set the kernel code text
>> back to "read-only" to keep the kernel code text protected.
>>
>> The issue happens when dynamic ftrace is tested at boot up. The test is
>> done before the kernel code text has been set to read-only. But the
>> "before" and "after" calls are still performed. The "after" call will
>> change the kernel code text to read-only prematurely, and other boot
>> code that expects this code to be read-write will fail.
>>
>> The solution is to add a variable that is set when the kernel code text
>> is expected to be converted to read-only, and make the ftrace "before"
>> and "after" calls do nothing if that variable is not yet set. This is
>> similar to the x86 solution from commit 162396309745 ("ftrace, x86:
>> make kernel text writable only for conversions").
>>
>> Reported-by: Stefan Agner <stefan@agner.ch>
>> Tested-by: Stefan Agner <stefan@agner.ch>
>> Link: http://lkml.kernel.org/r/20180620212906.24b7b66e@vmware.local.home
>> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>> ---
> 
> Perhaps I should have Cc'd stable too?
> 

As it is self tests only which are broken probably not super important.
But then, the fix is also rather clean and safe IMHO, so why not.

--
Stefan