Re: [RFC PATCH v1 1/1] tracing/kprobes: Return ENAMESVRLSYMS when func matches several symbols

Masami Hiramatsu
2023-08-23T23:55:13Z

Hi Francis,

On Wed, 23 Aug 2023 18:14:10 +0200
Francis Laniel <flaniel@linux.microsoft.com> wrote:

> Previously to this commit, if func matches several symbols, a PMU kprobe would
> be installed for the first matching address.
> This could lead to some misunderstanding when some BPF code was never called
> because it was attached to a function which was indeed not call, because the
> effectively called one has no kprobes.
>
> So, this commit introduces ENAMESVRLSYMS which is returned when func matches
> several symbols.

The trace_kprobe part looks good to me.
But sorry, I mislead you. I meant using an existing error code as a metaphor.
EINVAL is used everywhere, so choose another error code, e.g. EADDRNOTAVAIL.

Also, can you add this check in __trace_kprobe_create()?
I think right before below code, at that point, 'symbol' has the symbol name.

trace_probe_log_set_index(0);
if (event) {
ret = traceprobe_parse_event_name(&event, &group, gbuf,
event - argv[0]);
if (ret)
goto parse_error;
}

Thank you,

> This way, user needs to use addr to remove the ambiguity.
>
> Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
> Signed-off-by: Francis Laniel <flaniel@linux.microsoft.com>
> Link: https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kernel.org/
> ---
> arch/alpha/include/uapi/asm/errno.h | 2 ++
> arch/mips/include/uapi/asm/errno.h | 2 ++
> arch/parisc/include/uapi/asm/errno.h | 2 ++
> arch/sparc/include/uapi/asm/errno.h | 2 ++
> include/uapi/asm-generic/errno.h | 2 ++
> kernel/trace/trace_kprobe.c | 26 ++++++++++++++++++++++
> tools/arch/alpha/include/uapi/asm/errno.h | 2 ++
> tools/arch/mips/include/uapi/asm/errno.h | 2 ++
> tools/arch/parisc/include/uapi/asm/errno.h | 2 ++
> tools/arch/sparc/include/uapi/asm/errno.h | 2 ++
> tools/include/uapi/asm-generic/errno.h | 2 ++
> 11 files changed, 46 insertions(+)
>
> diff --git a/arch/alpha/include/uapi/asm/errno.h b/arch/alpha/include/uapi/asm/errno.h
> index 3d265f6babaf..3d9686d915f9 100644
> --- a/arch/alpha/include/uapi/asm/errno.h
> +++ b/arch/alpha/include/uapi/asm/errno.h
> @@ -125,4 +125,6 @@
>
> #define EHWPOISON 139 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 140 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/arch/mips/include/uapi/asm/errno.h b/arch/mips/include/uapi/asm/errno.h
> index 2fb714e2d6d8..1fd64ee7b629 100644
> --- a/arch/mips/include/uapi/asm/errno.h
> +++ b/arch/mips/include/uapi/asm/errno.h
> @@ -124,6 +124,8 @@
>
> #define EHWPOISON 168 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 169 /* Name correspond to several symbols */
> +
> #define EDQUOT 1133 /* Quota exceeded */
>
>
> diff --git a/arch/parisc/include/uapi/asm/errno.h b/arch/parisc/include/uapi/asm/errno.h
> index 87245c584784..c7845ceece26 100644
> --- a/arch/parisc/include/uapi/asm/errno.h
> +++ b/arch/parisc/include/uapi/asm/errno.h
> @@ -124,4 +124,6 @@
>
> #define EHWPOISON 257 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 258 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/arch/sparc/include/uapi/asm/errno.h b/arch/sparc/include/uapi/asm/errno.h
> index 81a732b902ee..1ed065943bab 100644
> --- a/arch/sparc/include/uapi/asm/errno.h
> +++ b/arch/sparc/include/uapi/asm/errno.h
> @@ -115,4 +115,6 @@
>
> #define EHWPOISON 135 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 136 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
> index cf9c51ac49f9..3d5d5740c8da 100644
> --- a/include/uapi/asm-generic/errno.h
> +++ b/include/uapi/asm-generic/errno.h
> @@ -120,4 +120,6 @@
>
> #define EHWPOISON 133 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 134 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 23dba01831f7..53b66db1ff53 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1699,6 +1699,16 @@ static int unregister_kprobe_event(struct trace_kprobe *tk)
> }
>
> #ifdef CONFIG_PERF_EVENTS
> +
> +static int count_symbols(void *data, unsigned long unused)
> +{
> + unsigned int *count = data;
> +
> + (*count)++;
> +
> + return 0;
> +}
> +
> /* create a trace_kprobe, but don't add it to global lists */
> struct trace_event_call *
> create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> @@ -1709,6 +1719,22 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> int ret;
> char *event;
>
> + /*
> + * If user specifies func, we check that the function name does not
> + * correspond to several symbols.
> + * If this is the case, we return with error code ENAMESVRLSYMS to
> + * indicate the user he/she should use addr and offs rather than func to
> + * remove the ambiguity.
> + */
> + if (func) {
> + unsigned int count;
> +
> + count = 0;
> + kallsyms_on_each_match_symbol(count_symbols, func, &count);
> + if (count > 1)
> + return ERR_PTR(-ENAMESVRLSYMS);
> + }
> +
> /*
> * local trace_kprobes are not added to dyn_event, so they are never
> * searched in find_trace_kprobe(). Therefore, there is no concern of
> diff --git a/tools/arch/alpha/include/uapi/asm/errno.h b/tools/arch/alpha/include/uapi/asm/errno.h
> index 3d265f6babaf..3d9686d915f9 100644
> --- a/tools/arch/alpha/include/uapi/asm/errno.h
> +++ b/tools/arch/alpha/include/uapi/asm/errno.h
> @@ -125,4 +125,6 @@
>
> #define EHWPOISON 139 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 140 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/tools/arch/mips/include/uapi/asm/errno.h b/tools/arch/mips/include/uapi/asm/errno.h
> index 2fb714e2d6d8..1fd64ee7b629 100644
> --- a/tools/arch/mips/include/uapi/asm/errno.h
> +++ b/tools/arch/mips/include/uapi/asm/errno.h
> @@ -124,6 +124,8 @@
>
> #define EHWPOISON 168 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 169 /* Name correspond to several symbols */
> +
> #define EDQUOT 1133 /* Quota exceeded */
>
>
> diff --git a/tools/arch/parisc/include/uapi/asm/errno.h b/tools/arch/parisc/include/uapi/asm/errno.h
> index 87245c584784..c7845ceece26 100644
> --- a/tools/arch/parisc/include/uapi/asm/errno.h
> +++ b/tools/arch/parisc/include/uapi/asm/errno.h
> @@ -124,4 +124,6 @@
>
> #define EHWPOISON 257 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 258 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/tools/arch/sparc/include/uapi/asm/errno.h b/tools/arch/sparc/include/uapi/asm/errno.h
> index 81a732b902ee..1ed065943bab 100644
> --- a/tools/arch/sparc/include/uapi/asm/errno.h
> +++ b/tools/arch/sparc/include/uapi/asm/errno.h
> @@ -115,4 +115,6 @@
>
> #define EHWPOISON 135 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 136 /* Name correspond to several symbols */
> +
> #endif
> diff --git a/tools/include/uapi/asm-generic/errno.h b/tools/include/uapi/asm-generic/errno.h
> index cf9c51ac49f9..3d5d5740c8da 100644
> --- a/tools/include/uapi/asm-generic/errno.h
> +++ b/tools/include/uapi/asm-generic/errno.h
> @@ -120,4 +120,6 @@
>
> #define EHWPOISON 133 /* Memory page has hardware error */
>
> +#define ENAMESVRLSYMS 134 /* Name correspond to several symbols */
> +
> #endif
> --
> 2.34.1
>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>