[PATCH 08/17] powerpc/ftrace: Refactor ftrace_modify_code()

[Christophe Leroy]

Le 19/06/2023 à 11:47, Naveen N Rao a écrit :
> Split up ftrace_modify_code() into a few helpers for future use. Also
> update error messages accordingly.
> 
> Signed-off-by: Naveen N Rao <naveen at kernel.org>

Reviewed-by: Christophe Leroy <christophe.leroy at csgroup.eu>

> ---
>   arch/powerpc/kernel/trace/ftrace.c | 51 +++++++++++++++++-------------
>   1 file changed, 29 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 913c7aa63d3fa3..ef4e49c2c37781 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -50,32 +50,39 @@ ftrace_call_replace(unsigned long ip, unsigned long addr, int link)
>   	return op;
>   }
>   
> -static inline int
> -ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
> +static inline int ftrace_read_inst(unsigned long ip, ppc_inst_t *op)
>   {
> -	ppc_inst_t replaced;
> -
> -	/*
> -	 * Note:
> -	 * We are paranoid about modifying text, as if a bug was to happen, it
> -	 * could cause us to read or write to someplace that could cause harm.
> -	 * Carefully read and modify the code with probe_kernel_*(), and make
> -	 * sure what we read is what we expected it to be before modifying it.
> -	 */
> -
> -	/* read the text we want to modify */
> -	if (copy_inst_from_kernel_nofault(&replaced, (void *)ip))
> +	if (copy_inst_from_kernel_nofault(op, (void *)ip)) {
> +		pr_err("0x%lx: fetching instruction failed\n", ip);
>   		return -EFAULT;
> -
> -	/* Make sure it is what we expect it to be */
> -	if (!ppc_inst_equal(replaced, old)) {
> -		pr_err("%p: replaced (%08lx) != old (%08lx)", (void *)ip,
> -		       ppc_inst_as_ulong(replaced), ppc_inst_as_ulong(old));
> -		return -EINVAL;
>   	}
>   
> -	/* replace the text with the new text */
> -	return patch_instruction((u32 *)ip, new);
> +	return 0;
> +}
> +
> +static inline int ftrace_validate_inst(unsigned long ip, ppc_inst_t inst)
> +{
> +	ppc_inst_t op;
> +	int ret;
> +
> +	ret = ftrace_read_inst(ip, &op);
> +	if (!ret && !ppc_inst_equal(op, inst)) {
> +		pr_err("0x%lx: expected (%08lx) != found (%08lx)\n",
> +		       ip, ppc_inst_as_ulong(inst), ppc_inst_as_ulong(op));
> +		ret = -EINVAL;
> +	}
> +
> +	return ret;
> +}
> +
> +static inline int ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
> +{
> +	int ret = ftrace_validate_inst(ip, old);
> +
> +	if (!ret)
> +		ret = patch_instruction((u32 *)ip, new);
> +
> +	return ret;
>   }
>   
>   /*