Re: [PATCH] tracing/kprobes: Fix symbol counting logic by looking at modules as well

[Francis Laniel <flaniel@linux.microsoft.com>]

Hi!


Le samedi 28 octobre 2023, 02:31:26 EET Andrii Nakryiko a écrit :
> Recent changes to count number of matching symbols when creating
> a kprobe event failed to take into account kernel modules. As such, it
> breaks kprobes on kernel module symbols, by assuming there is no match.

Ah... Sorry about this...
Thank you for the fix, I will handle the patch for older kernels in case there 
are troubles applying it.
 
> Fix this my calling module_kallsyms_on_each_symbol() in addition to
> kallsyms_on_each_match_symbol() to perform a proper counting.
> 
> Cc: Francis Laniel <flaniel@linux.microsoft.com>
> Cc: stable@vger.kernel.org
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Fixes: b022f0c7e404 ("tracing/kprobes: Return EADDRNOTAVAIL when func
> matches several symbols") Signed-off-by: Andrii Nakryiko
> <andrii@kernel.org>
> ---
>  kernel/trace/trace_kprobe.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index effcaede4759..1efb27f35963 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -714,14 +714,30 @@ static int count_symbols(void *data, unsigned long
> unused) return 0;
>  }
> 
> +struct sym_count_ctx {
> +	unsigned int count;
> +	const char *name;
> +};
> +
> +static int count_mod_symbols(void *data, const char *name, unsigned long
> unused) +{
> +	struct sym_count_ctx *ctx = data;
> +
> +	if (strcmp(name, ctx->name) == 0)
> +		ctx->count++;
> +
> +	return 0;
> +}
> +
>  static unsigned int number_of_same_symbols(char *func_name)
>  {
> -	unsigned int count;
> +	struct sym_count_ctx ctx = { .count = 0, .name = func_name };
> +
> +	kallsyms_on_each_match_symbol(count_symbols, func_name, &ctx.count);
> 
> -	count = 0;
> -	kallsyms_on_each_match_symbol(count_symbols, func_name, &count);
> +	module_kallsyms_on_each_symbol(NULL, count_mod_symbols, &ctx);
> 
> -	return count;
> +	return ctx.count;
>  }
> 
>  static int __trace_kprobe_create(int argc, const char *argv[])


Best regards.