lkml.org 
[lkml]   [2020]   [Mar]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 8/8] riscv: add two hook functions of ftrace
From
On Mon, 17 Feb 2020 00:32:23 PST (-0800), zong.li@sifive.com wrote:
> After the text section be mask as non-writable, the ftrace have to
> change the permission of text for dynamic patching the intructions.
> Add ftrace_arch_code_modify_prepare and
> ftrace_arch_code_modify_post_process to change permission.
>
> Signed-off-by: Zong Li <zong.li@sifive.com>
> ---
> arch/riscv/kernel/ftrace.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index c40fdcdeb950..576df0807200 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -7,9 +7,27 @@
>
> #include <linux/ftrace.h>
> #include <linux/uaccess.h>
> +#include <linux/memory.h>
> +#include <asm/set_memory.h>
> #include <asm/cacheflush.h>
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> +int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
> +{
> + mutex_lock(&text_mutex);
> + set_kernel_text_rw();
> + set_all_modules_text_rw();
> + return 0;
> +}

None of the other architectures are doing anything remotely like this in these
functions, despite many supporting STRICT_KERNEL_RWX. Having a function that
maps all text as RW seems super dangerous, as one stack attack means NX is
gone.

Looks like FIX_TEXT_POKE0 is the magic that makes the other ports work.

> +
> +int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
> +{
> + set_all_modules_text_ro();
> + set_kernel_text_ro();
> + mutex_unlock(&text_mutex);
> + return 0;
> +}

Presumably this needs a icache flush as well? Probably better to do so when
installing the instructions, though.

> +
> static int ftrace_check_current_call(unsigned long hook_pos,
> unsigned int *expected)
> {

\
 
 \ /
  Last update: 2020-03-05 02:45    [W:0.128 / U:0.464 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site