Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
On Tue, 24 Mar 2026 09:05:12 +0100 Martin Kaiser wrote: > Thus wrote Masami Hiramatsu ([email protected]): > > > On Mon, 23 Mar 2026 10:48:18 -0400 > > Steven Rostedt wrote: > > > > On Mon, 23 Mar 2026 11:19:36 +0100 > > > Martin Kaiser wrote: > > > > > If fprobe_entry does not fill the allocated fgraph_data completely, the > > > > unused part is zeroed with memset. > > > > > Fix the length for this memset call. Both reserved_words and used are in > > > > units of return stack words, but memset needs the number of bytes. > > > > > Cc: [email protected] > > > > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") > > > > Signed-off-by: Martin Kaiser > > > > --- > > > > kernel/trace/fprobe.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > > > > index dcadf1d23b8a..6a1192515afd 100644 > > > > --- a/kernel/trace/fprobe.c > > > > +++ b/kernel/trace/fprobe.c > > > > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct > > > > ftrace_graph_ent *trace, struct fgraph_ops > > > > } > > > > } > > > > if (used < reserved_words) > > > > - memset(fgraph_data + used, 0, reserved_words - used); > > > > + memset(fgraph_data + used, 0, (reserved_words - used) * > > > > sizeof(long)); > > > > So fgraph_data is only used internally between the fprobe_fgraph_entry() > > > and fprobe_return() as it only exists on the fgraph shadow stack. I'm not > > > even sure if the unused portion needs to be zeroed out. > > > > Thus, this may be correct, but it doesn't look like a true bug that needs > > > a > > > stable tag. > > > Hmm, indeed. Maybe we'd better just remove this memset from for-next. > > Ok, I see your point. I'll send a v2 that removes the memset. Yeah, thanks! > > Best regards, > Martin > > > Thanks, > > > > > -- Steve > > > > > > > /* If any exit_handler is set, data must be used. */ > > > > return used != 0; > > > > > -- > > Masami Hiramatsu (Google) -- Masami Hiramatsu (Google)
Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
Thus wrote Masami Hiramatsu ([email protected]): > On Mon, 23 Mar 2026 10:48:18 -0400 > Steven Rostedt wrote: > > On Mon, 23 Mar 2026 11:19:36 +0100 > > Martin Kaiser wrote: > > > If fprobe_entry does not fill the allocated fgraph_data completely, the > > > unused part is zeroed with memset. > > > Fix the length for this memset call. Both reserved_words and used are in > > > units of return stack words, but memset needs the number of bytes. > > > Cc: [email protected] > > > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") > > > Signed-off-by: Martin Kaiser > > > --- > > > kernel/trace/fprobe.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > > > index dcadf1d23b8a..6a1192515afd 100644 > > > --- a/kernel/trace/fprobe.c > > > +++ b/kernel/trace/fprobe.c > > > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct > > > ftrace_graph_ent *trace, struct fgraph_ops > > > } > > > } > > > if (used < reserved_words) > > > - memset(fgraph_data + used, 0, reserved_words - used); > > > + memset(fgraph_data + used, 0, (reserved_words - used) * > > > sizeof(long)); > > So fgraph_data is only used internally between the fprobe_fgraph_entry() > > and fprobe_return() as it only exists on the fgraph shadow stack. I'm not > > even sure if the unused portion needs to be zeroed out. > > Thus, this may be correct, but it doesn't look like a true bug that needs a > > stable tag. > Hmm, indeed. Maybe we'd better just remove this memset from for-next. Ok, I see your point. I'll send a v2 that removes the memset. Best regards, Martin > Thanks, > > -- Steve > > > /* If any exit_handler is set, data must be used. */ > > > return used != 0; > -- > Masami Hiramatsu (Google)
Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
On Mon, 23 Mar 2026 10:48:18 -0400 Steven Rostedt wrote: > On Mon, 23 Mar 2026 11:19:36 +0100 > Martin Kaiser wrote: > > > If fprobe_entry does not fill the allocated fgraph_data completely, the > > unused part is zeroed with memset. > > > > Fix the length for this memset call. Both reserved_words and used are in > > units of return stack words, but memset needs the number of bytes. > > > > Cc: [email protected] > > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") > > Signed-off-by: Martin Kaiser > > --- > > kernel/trace/fprobe.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > > index dcadf1d23b8a..6a1192515afd 100644 > > --- a/kernel/trace/fprobe.c > > +++ b/kernel/trace/fprobe.c > > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent > > *trace, struct fgraph_ops > > } > > } > > if (used < reserved_words) > > - memset(fgraph_data + used, 0, reserved_words - used); > > + memset(fgraph_data + used, 0, (reserved_words - used) * > > sizeof(long)); > > So fgraph_data is only used internally between the fprobe_fgraph_entry() > and fprobe_return() as it only exists on the fgraph shadow stack. I'm not > even sure if the unused portion needs to be zeroed out. > > Thus, this may be correct, but it doesn't look like a true bug that needs a > stable tag. Hmm, indeed. Maybe we'd better just remove this memset from for-next. Thanks, > > -- Steve > > > > > > /* If any exit_handler is set, data must be used. */ > > return used != 0; > -- Masami Hiramatsu (Google)
Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
On Mon, 23 Mar 2026 11:19:36 +0100 Martin Kaiser wrote: > If fprobe_entry does not fill the allocated fgraph_data completely, the > unused part is zeroed with memset. > > Fix the length for this memset call. Both reserved_words and used are in > units of return stack words, but memset needs the number of bytes. > > Cc: [email protected] > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") > Signed-off-by: Martin Kaiser > --- > kernel/trace/fprobe.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > index dcadf1d23b8a..6a1192515afd 100644 > --- a/kernel/trace/fprobe.c > +++ b/kernel/trace/fprobe.c > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent > *trace, struct fgraph_ops > } > } > if (used < reserved_words) > - memset(fgraph_data + used, 0, reserved_words - used); > + memset(fgraph_data + used, 0, (reserved_words - used) * > sizeof(long)); So fgraph_data is only used internally between the fprobe_fgraph_entry() and fprobe_return() as it only exists on the fgraph shadow stack. I'm not even sure if the unused portion needs to be zeroed out. Thus, this may be correct, but it doesn't look like a true bug that needs a stable tag. -- Steve > > /* If any exit_handler is set, data must be used. */ > return used != 0;
Re: [PATCH] tracing: fprobe: fix the length of unused fgraph_data
On Mon, 23 Mar 2026 11:19:36 +0100 Martin Kaiser wrote: > If fprobe_entry does not fill the allocated fgraph_data completely, the > unused part is zeroed with memset. > > Fix the length for this memset call. Both reserved_words and used are in > units of return stack words, but memset needs the number of bytes. > > Cc: [email protected] > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") > Signed-off-by: Martin Kaiser Good catch! Thanks, > --- > kernel/trace/fprobe.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > index dcadf1d23b8a..6a1192515afd 100644 > --- a/kernel/trace/fprobe.c > +++ b/kernel/trace/fprobe.c > @@ -451,7 +451,7 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent > *trace, struct fgraph_ops > } > } > if (used < reserved_words) > - memset(fgraph_data + used, 0, reserved_words - used); > + memset(fgraph_data + used, 0, (reserved_words - used) * > sizeof(long)); > > /* If any exit_handler is set, data must be used. */ > return used != 0; > -- > 2.43.7 > -- Masami Hiramatsu (Google)
