Re: [PATCH v5 16/18] arm64: ftrace: use function_nocfi for ftrace_call

[Mark Rutland]

On Thu, Apr 01, 2021 at 04:32:14PM -0700, Sami Tolvanen wrote:
> With CONFIG_CFI_CLANG, the compiler replaces function pointers with
> jump table addresses, which breaks dynamic ftrace as the address of
> ftrace_call is replaced with the address of ftrace_call.cfi_jt. Use
> function_nocfi() to get the address of the actual function instead.
> 
> Suggested-by: Ben Dai <ben.dai@xxxxxxxxxx>
> Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 86a5cf9bc19a..b5d3ddaf69d9 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -55,7 +55,7 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
>  	unsigned long pc;
>  	u32 new;
>  
> -	pc = (unsigned long)&ftrace_call;
> +	pc = (unsigned long)function_nocfi(ftrace_call);

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

Thanks,
Mark.

>  	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
>  					  AARCH64_INSN_BRANCH_LINK);
>  
> -- 
> 2.31.0.208.g409f899ff0-goog
>