Re: [PATCH] perf trace: Fix segmentation fault when access syscall info

[Leo Yan]

On Fri, Aug 09, 2019 at 10:25:22AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Aug 09, 2019 at 06:47:52PM +0800, Leo Yan escreveu:
> > 'perf trace' reports the segmentation fault as below on Arm64:
> > 
> >   # perf trace -e string -e augmented_raw_syscalls.c
> >   LLVM: dumping tools/perf/examples/bpf/augmented_raw_syscalls.o
> >   perf: Segmentation fault
> >   Obtained 12 stack frames.
> >   perf(sighandler_dump_stack+0x47) [0xaaaaac96ac87]
> >   linux-vdso.so.1(+0x5b7) [0xffffadbeb5b7]
> >   /lib/aarch64-linux-gnu/libc.so.6(strlen+0x10) [0xfffface7d5d0]
> >   /lib/aarch64-linux-gnu/libc.so.6(_IO_vfprintf+0x1ac7) [0xfffface49f97]
> >   /lib/aarch64-linux-gnu/libc.so.6(__vsnprintf_chk+0xc7) [0xffffacedfbe7]
> >   perf(scnprintf+0x97) [0xaaaaac9ca3ff]
> >   perf(+0x997bb) [0xaaaaac8e37bb]
> >   perf(cmd_trace+0x28e7) [0xaaaaac8ec09f]
> >   perf(+0xd4a13) [0xaaaaac91ea13]
> >   perf(main+0x62f) [0xaaaaac8a147f]
> >   /lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0xe3) [0xfffface22d23]
> >   perf(+0x57723) [0xaaaaac8a1723]
> >   Segmentation fault
> > 
> > This issue is introduced by commit 30a910d7d3e0 ("perf trace:
> > Preallocate the syscall table"), it allocates trace->syscalls.table[]
> > array and the element count is 'trace->sctbl->syscalls.nr_entries';
> > but on Arm64, the system call number is not continuously used; e.g. the
> > syscall maximum id is 436 but the real entries is only 281.  So the
> > table is allocated with 'nr_entries' as the element count, but it
> > accesses the table with the syscall id, which might be out of the bound
> > of the array and cause the segmentation fault.
> > 
> > This patch allocates trace->syscalls.table[] with the element count is
> > 'trace->sctbl->syscalls.max_id + 1', this allows any id to access the
> > table without out of the bound.
> 
> Thanks a lot!

You are welcome, Arnaldo.

> My bad, that is why we have that max_id there, I forgot
> about it and since I tested so far only on x86_64... applied to
> perf/core, since it is only on:
> 
> [acme@quaco perf]$ git tag --contains 30a910d7d3e0
> perf-core-for-mingo-5.4-20190729
> [acme@quaco perf]$

Thanks!  Yes, I am working on perf/core branch and hit this issue.

Just in case Ingo has not merged your PR, if could save your efforts
it's quite fine for me to merge this change in your original patch.

Thanks,
Leo Yan

> 
> - Arnaldo
>  
> > Fixes: 30a910d7d3e0 ("perf trace: Preallocate the syscall table")
> > Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> > ---
> >  tools/perf/builtin-trace.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index 75eb3811e942..d553d06a9aeb 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -1492,7 +1492,7 @@ static int trace__read_syscall_info(struct trace *trace, int id)
> >  	const char *name = syscalltbl__name(trace->sctbl, id);
> >  
> >  	if (trace->syscalls.table == NULL) {
> > -		trace->syscalls.table = calloc(trace->sctbl->syscalls.nr_entries, sizeof(*sc));
> > +		trace->syscalls.table = calloc(trace->sctbl->syscalls.max_id + 1, sizeof(*sc));
> >  		if (trace->syscalls.table == NULL)
> >  			return -ENOMEM;
> >  	}
> > -- 
> > 2.17.1
> 
> -- 
> 
> - Arnaldo