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

Hi.

Le jeudi 24 août 2023, 01:53:55 CEST Masami Hiramatsu a écrit :

Hi Francis,

On Wed, 23 Aug 2023 18:14:10 +0200

Francis Laniel [off-list ref] wrote:

quoted

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.

No problem, I was a bit in doubt regarding adding a new error code, but at 
least I learnt how to do it if one day I need to do so!
But yes, for this case, better to use an existing one!

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;
        }

Addressed in v2, thank you!

Thank you,

quoted

This way, user needs to use addr to remove the ambiguity.

Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Francis Laniel <redacted>
Link:
https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kern
el.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

quoted

+	 * 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

Best regards.