On 04.07.2018 13:30, Stefan Agner wrote:
> On 21.06.2018 18:47, Steven Rostedt wrote:
>> From: Steven Rostedt (VMware) <rost...@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 <ste...@agner.ch>
>> Tested-by: Stefan Agner <ste...@agner.ch>
>> Link: http://lkml.kernel.org/r/20180620212906.24b7b...@vmware.local.home
>> Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
>> ---
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index c186474422f3..0cc8e04295a4 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c
>
> I guess this can be seen as reviewed?
>
> Patches touching core ARM port usually go through Russels patch tracker.
>
> You have to submit the patch here:
> http://www.armlinux.org.uk/developer/patches/
>
FWIW, I added this patch to the patch tracker, its patch ID is 8780/1.
--
Stefan
>
>
>> @@ -736,20 +736,29 @@ static int __mark_rodata_ro(void *unused)
>> return 0;
>> }
>>
>> +static int kernel_set_to_readonly __read_mostly;
>> +
>> void mark_rodata_ro(void)
>> {
>> + kernel_set_to_readonly = 1;
>> stop_machine(__mark_rodata_ro, NULL, NULL);
>> debug_checkwx();
>> }
>>
>> void set_kernel_text_rw(void)
>> {
>> + if (!kernel_set_to_readonly)
>> + return;
>> +
>> set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), false,
>> current->active_mm);
>> }
>>
>> void set_kernel_text_ro(void)
>> {
>> + if (!kernel_set_to_readonly)
>> + return;
>> +
>> set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
>> current->active_mm);
>> }
