On Thu, Jun 27, 2019 at 09:18:19PM -0400, Steven Rostedt wrote:
>
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
>
> Taking the text_mutex in ftrace_arch_code_modify_prepare() is to fix a
> race against module loading and live kernel patching that might try to
> change the text permissions while ftrace has it as read/write. This
> really needs to be documented in the code. Add a comment that does such.
>
> Suggested-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
> arch/x86/kernel/ftrace.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 33786044d5ac..d7e93b2783fd 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -36,6 +36,11 @@
>
> int ftrace_arch_code_modify_prepare(void)
> {
> + /*
> + * Need to grab text_mutex to prevent a race from module loading
> + * and live kernel patching from changing the text permissions while
> + * ftrace has it set to "read/write".
> + */
> mutex_lock(&text_mutex);
> set_kernel_text_rw();
> set_all_modules_text_rw();
> --
> 2.20.1
>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
--
Josh
