linux-kernel - Re: perf-probe crash in dwarf_getcfi

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Date:	Tue, 30 Dec 2014 18:05:33 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mark Wielaard <mjw@...hat.com>
Subject: Re: perf-probe crash in dwarf_getcfi_elf

On Tue, Dec 30, 2014 at 05:47:08PM +0900, Namhyung Kim wrote:
> On Mon, Dec 29, 2014 at 09:39:18PM -0700, David Ahern wrote:
> > Hi Namhyung:
> > 
> > Using perf-probe from top of Linus' tree I get a segfault on both Fedora 16
> > and 18 (does not crash on Fedora 20). Command used is:
> > 
> > perf probe -x /lib64/libc-2.14.90.so -a 'malloc  size=%di'
> > 
> > git bisect points to:
> > 
> > commit 03d89412981a7681971bc77edba1669595763030
> > Author: Namhyung Kim <namhyung@...nel.org>
> > Date:   Mon Apr 7 16:05:48 2014 +0900
> > 
> >     perf probe: Use dwarf_getcfi_elf() instead of dwarf_getcfi()
> > 
> 
> It seems to be related to below commit in elfutils.  We might need to
> check .eh_frame section has SHT_PROGBITS.  Will send a patch soon.


>From f56964e74d60a9921214d0e2e5c3d082f5a910c1 Mon Sep 17 00:00:00 2001
From: Namhyung Kim <namhyung@...nel.org>
Date: Tue, 30 Dec 2014 17:47:47 +0900
Subject: [PATCH] perf probe: Fix a segfault on old libdw

David reported that perf can segfault when adding an uprobe event like
this:

  $ perf probe -x /lib64/libc-2.14.90.so -a 'malloc  size=%di'

  (gdb) bt
  #0  parse_eh_frame_hdr (hdr=0x0, hdr_size=2596, hdr_vaddr=71788,
      ehdr=0x7fffffffd390, eh_frame_vaddr=
      0x7fffffffd378, table_entries=0x8808d8, table_encoding=0x8808e0 "") at
      dwarf_getcfi_elf.c:79
  #1  0x000000385f81615a in getcfi_scn_eh_frame (hdr_vaddr=71788,
      hdr_scn=0x8839b0, shdr=0x7fffffffd2f0, scn=<optimized out>,
      ehdr=0x7fffffffd390, elf=0x882b30) at dwarf_getcfi_elf.c:231
  #2  getcfi_shdr (ehdr=0x7fffffffd390, elf=0x882b30) at dwarf_getcfi_elf.c:283
  #3  dwarf_getcfi_elf (elf=0x882b30) at dwarf_getcfi_elf.c:309
  #4  0x00000000004d5bac in debuginfo__find_probes (pf=0x7fffffffd4f0,
      dbg=Unhandled dwarf expression opcode 0xfa) at util/probe-finder.c:993
  #5  0x00000000004d634a in debuginfo__find_trace_events (dbg=0x880840,
      pev=<optimized out>, tevs=0x880f88, max_tevs=<optimized out>) at
      util/probe-finder.c:1200
  #6  0x00000000004aed6b in try_to_find_probe_trace_events (target=0x881b20
      "/lib64/libpthread-2.14.90.so",
      max_tevs=128, tevs=0x880f88, pev=0x859b30) at util/probe-event.c:482
  #7  convert_to_probe_trace_events (target=0x881b20
      "/lib64/libpthread-2.14.90.so", max_tevs=128, tevs=0x880f88,
      pev=0x859b30) at util/probe-event.c:2356
  #8  add_perf_probe_events (pevs=<optimized out>, npevs=1, max_tevs=128,
      target=0x881b20 "/lib64/libpthread-2.14.90.so", force_add=false) at
      util/probe-event.c:2391
  #9  0x000000000044014f in __cmd_probe (argc=<optimized out>,
      argv=0x7fffffffe2f0, prefix=Unhandled dwarf expression opcode 0xfa) at
      at builtin-probe.c:488
  #10 0x0000000000440313 in cmd_probe (argc=5, argv=0x7fffffffe2f0,
      prefix=<optimized out>) at builtin-probe.c:506
  #11 0x000000000041d133 in run_builtin (p=0x805680, argc=5,
      argv=0x7fffffffe2f0) at perf.c:341
  #12 0x000000000041c8b2 in handle_internal_command (argv=<optimized out>,
      argc=<optimized out>) at perf.c:400
  #13 run_argv (argv=<optimized out>, argcp=<optimized out>) at perf.c:444
  #14 main (argc=5, argv=0x7fffffffe2f0) at perf.c:559

And I found a related commit (5704c8c4fa71 "getcfi_scn_eh_frame: Don't
crash and burn when .eh_frame bits aren't there.") in elfutils that
can lead to a unexpected crash like this.  To safely use the function,
it needs to check the .eh_frame section is a PROGBITS type.

Reported-by: David Ahern <dsahern@...il.com>
Cc: Mark Wielaard <mjw@...hat.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/util/probe-finder.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index c7918f83b300..b5247d777f0e 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -989,8 +989,24 @@ static int debuginfo__find_probes(struct debuginfo *dbg,
 	int ret = 0;
 
 #if _ELFUTILS_PREREQ(0, 142)
+	Elf *elf;
+	GElf_Ehdr ehdr;
+	GElf_Shdr shdr;
+
 	/* Get the call frame information from this dwarf */
-	pf->cfi = dwarf_getcfi_elf(dwarf_getelf(dbg->dbg));
+	elf = dwarf_getelf(dbg->dbg);
+	if (elf == NULL)
+		return -EINVAL;
+
+	if (gelf_getehdr(elf, &ehdr) == NULL)
+		return -EINVAL;
+
+	if (elf_section_by_name(elf, &ehdr, &shdr, ".eh_frame", NULL) &&
+	    shdr.sh_type == SHT_PROGBITS) {
+		pf->cfi = dwarf_getcfi_elf(elf);
+	} else {
+		pf->cfi = dwarf_getcfi(dbg->dbg);
+	}
 #endif
 
 	off = 0;
-- 
2.1.3

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