linux-kernel - Re: [PATCH v4 3/9] riscv: patch code by fixmap mapping

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Message-Id: <20200408010218.c601beb496712a1251e2c9a0@kernel.org>
Date:   Wed, 8 Apr 2020 01:02:18 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Zong Li <zong.li@...ive.com>
Cc:     palmer@...belt.com, paul.walmsley@...ive.com,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/9] riscv: patch code by fixmap mapping

On Tue,  7 Apr 2020 22:46:48 +0800
Zong Li <zong.li@...ive.com> wrote:

> On strict kernel memory permission, the ftrace have to change the
> permission of text for dynamic patching the intructions. Use
> riscv_patch_text_nosync() to patch code instead of probe_kernel_write.
> 
> Signed-off-by: Zong Li <zong.li@...ive.com>
> Suggested-by: Masami Hiramatsu <mhiramat@...nel.org>

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks!

> ---
>  arch/riscv/kernel/ftrace.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index c40fdcdeb950..08396614d6f4 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -7,9 +7,23 @@
>  
>  #include <linux/ftrace.h>
>  #include <linux/uaccess.h>
> +#include <linux/memory.h>
>  #include <asm/cacheflush.h>
> +#include <asm/patch.h>
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
> +{
> +	mutex_lock(&text_mutex);
> +	return 0;
> +}
> +
> +int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
> +{
> +	mutex_unlock(&text_mutex);
> +	return 0;
> +}
> +
>  static int ftrace_check_current_call(unsigned long hook_pos,
>  				     unsigned int *expected)
>  {
> @@ -46,20 +60,14 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
>  {
>  	unsigned int call[2];
>  	unsigned int nops[2] = {NOP4, NOP4};
> -	int ret = 0;
>  
>  	make_call(hook_pos, target, call);
>  
> -	/* replace the auipc-jalr pair at once */
> -	ret = probe_kernel_write((void *)hook_pos, enable ? call : nops,
> -				 MCOUNT_INSN_SIZE);
> -	/* return must be -EPERM on write error */
> -	if (ret)
> +	/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
> +	if (patch_text_nosync
> +	    ((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE))
>  		return -EPERM;
>  
> -	smp_mb();
> -	flush_icache_range((void *)hook_pos, (void *)hook_pos + MCOUNT_INSN_SIZE);
> -
>  	return 0;
>  }
>  
> -- 
> 2.26.0
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>