[PATCH 2/3] perf record: Fix crash when kptr is restricted

From: Arnaldo Carvalho de Melo
Date: Fri May 27 2016 - 11:57:38 EST

From: Wang Nan <wangnan0@xxxxxxxxxx>

Before this patch, a simple 'perf record' could fail if kptr_restrict is
set to 1 (for normal user) or 2 (for root):

# perf record ls
WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted,
check /proc/sys/kernel/kptr_restrict.

Samples in kernel functions may not be resolved if a suitable vmlinux
file is not found in the buildid cache or in the vmlinux path.

Samples in kernel modules won't be resolved at all.

If some relocation was applied (e.g. kexec) symbols may be misresolved
even with a suitable vmlinux or kallsyms file.

Segmentation fault (core dumped)

This patch skips perf_event__synthesize_kernel_mmap() when kptr is not

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Fixes: 45e90056904b ("perf machine: Do not bail out if not managing to read ref reloc symbol")
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Link: http://lkml.kernel.org/r/1464081688-167940-2-git-send-email-wangnan0@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
tools/perf/util/event.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index f6fcc6832949..9b141f12329e 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -673,6 +673,8 @@ int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
int err;
union perf_event *event;

+ if (symbol_conf.kptr_restrict)
+ return -1;
if (map == NULL)
return -1;