lkml.org 
[lkml]   [2019]   [May]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] tracing: silence GCC 9 array bounds warning
On Fri, 17 May 2019 11:25:02 +0200
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:

> Starting with GCC 9, -Warray-bounds detects cases when memset is called
> starting on a member of a struct but the size to be cleared ends up
> writing over further members.
>
> Such a call happens in the trace code to clear, at once, all members
> after and including `seq` on struct trace_iterator:
>
> In function 'memset',
> inlined from 'ftrace_dump' at kernel/trace/trace.c:8914:3:
> ./include/linux/string.h:344:9: warning: '__builtin_memset' offset
> [8505, 8560] from the object at 'iter' is out of the bounds of
> referenced subobject 'seq' with type 'struct trace_seq' at offset
> 4368 [-Warray-bounds]
> 344 | return __builtin_memset(p, c, size);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> In order to avoid GCC complaining about it, we compute the address
> ourselves by adding the offsetof distance instead of referring
> directly to the member.
>
> Since there are two places doing this clear (trace.c and trace_kdb.c),
> take the chance to move the workaround into a single place in
> the internal header.

Hi Miguel,

Linus mentioned this too.

https://lore.kernel.org/lkml/CAHk-=wihYB8w__YQjgYjYZsVniu5CtkTcFycmCGdqVg8GUje7g@mail.gmail.com/T/#u

I was going to do a helper function, and put it in the queue for the
next merge window (as it isn't really a bug, just gcc complaining a
little more aggressively). But since you already did the patch, I'll
use yours. But I have some nits about it below.


Add here:

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/CAHk-=wihYB8w__YQjgYjYZsVniu5CtkTcFycmCGdqVg8GUje7g@mail.gmail.com

>
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> ---
> kernel/trace/trace.c | 7 +------
> kernel/trace/trace.h | 14 ++++++++++++++
> kernel/trace/trace_kdb.c | 7 +------
> 3 files changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ca1ee656d6d8..37990532351b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -8627,12 +8627,7 @@ void ftrace_dump(enum ftrace_dump_mode
> oops_dump_mode)
> cnt++;
>
> - /* reset all but tr, trace, and overruns */
> - memset(&iter.seq, 0,
> - sizeof(struct trace_iterator) -
> - offsetof(struct trace_iterator, seq));
> - iter.iter_flags |= TRACE_FILE_LAT_FMT;

Setting the LAT_FMT isn't something a function called "reset" should do.

> - iter.pos = -1;
> + trace_iterator_reset(&iter);
>
> if (trace_find_next_entry_inc(&iter) != NULL) {
> int ret;
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index d80cee49e0eb..80ad656f43eb 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1964,4 +1964,18 @@ static inline void
> tracer_hardirqs_off(unsigned long a0, unsigned long a1) { }
> extern struct trace_iterator *tracepoint_print_iter;
>
> +/* reset all but tr, trace, and overruns */
> +static __always_inline void trace_iterator_reset(struct
> trace_iterator * iter) +{
> + /*
> + * Equivalent to &iter->seq, but avoids GCC 9 complaining
> about
> + * overwriting more members than just iter->seq
> (-Warray-bounds)
> + */
> + memset((char *)(iter) + offsetof(struct trace_iterator,

Why (char *)? Please use (void *).

> seq), 0,
> + sizeof(struct trace_iterator) -
> + offsetof(struct trace_iterator, seq));

Make a variable for offset and reuse that (see Linus's email).

> + iter->iter_flags |= TRACE_FILE_LAT_FMT;

Again, leave the LAT_FMT change in the other locations.

Please send a v2 version with these updates.

Thanks!

-- Steve

> + iter->pos = -1;
> +}
> +
> #endif /* _LINUX_KERNEL_TRACE_H */
> diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
> index 810d78a8d14c..0a2a166ee716 100644
> --- a/kernel/trace/trace_kdb.c
> +++ b/kernel/trace/trace_kdb.c
> @@ -41,12 +41,7 @@ static void ftrace_dump_buf(int skip_lines, long
> cpu_file)
> kdb_printf("Dumping ftrace buffer:\n");
>
> - /* reset all but tr, trace, and overruns */
> - memset(&iter.seq, 0,
> - sizeof(struct trace_iterator) -
> - offsetof(struct trace_iterator, seq));
> - iter.iter_flags |= TRACE_FILE_LAT_FMT;
> - iter.pos = -1;
> + trace_iterator_reset(&iter);
>
> if (cpu_file == RING_BUFFER_ALL_CPUS) {
> for_each_tracing_cpu(cpu) {

\
 
 \ /
  Last update: 2019-05-17 18:48    [W:0.097 / U:138.508 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site