From: Thomas Richter tmricht@linux.ibm.com
[ Upstream commit 2bbc83537614517730e9f2811195004b712de207 ]
This test places a kprobe to function getname_flags() in the kernel which has the following prototype:
struct filename *getname_flags(const char __user *filename, int flags, int *empty)
The 'filename' argument points to a filename located in user space memory.
Looking at commit 88903c464321c ("tracing/probe: Add ustring type for user-space string") the kprobe should indicate that user space memory is accessed.
Output before:
[root@m35lp76 perf]# ./perf test 66 67 66: Use vfs_getname probe to get syscall args filenames : FAILED! 67: Check open filename arg using perf trace + vfs_getname: FAILED! [root@m35lp76 perf]#
Output after:
[root@m35lp76 perf]# ./perf test 66 67 66: Use vfs_getname probe to get syscall args filenames : Ok 67: Check open filename arg using perf trace + vfs_getname: Ok [root@m35lp76 perf]#
Comments from Masami Hiramatsu:
This bug doesn't happen on x86 or other archs on which user address space and kernel address space is the same. On some arches (ppc64 in this case?) user address space is partially or completely the same as kernel address space.
(Yes, they switch the world when running into the kernel) In this case, we need to use different data access functions for each space.
That is why I introduced the "ustring" type for kprobe events.
As far as I can see, Thomas's patch is sane. Thomas, could you show us your result on your test environment?
Comments from Thomas Richter:
Test results for s/390 included above.
Signed-off-by: Thomas Richter tmricht@linux.ibm.com Acked-by: Masami Hiramatsu mhiramat@kernel.org Tested-by: Arnaldo Carvalho de Melo acme@redhat.com Cc: Heiko Carstens heiko.carstens@de.ibm.com Cc: Sumanth Korikkar sumanthk@linux.ibm.com Cc: Vasily Gorbik gor@linux.ibm.com Link: http://lore.kernel.org/lkml/20200217102111.61137-1-tmricht@linux.ibm.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/perf/tests/shell/lib/probe_vfs_getname.sh | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/tests/shell/lib/probe_vfs_getname.sh b/tools/perf/tests/shell/lib/probe_vfs_getname.sh index 068d463e5cbfc..4b0922a209701 100644 --- a/tools/perf/tests/shell/lib/probe_vfs_getname.sh +++ b/tools/perf/tests/shell/lib/probe_vfs_getname.sh @@ -14,7 +14,7 @@ add_probe_vfs_getname() { if [ $had_vfs_getname -eq 1 ] ; then line=$(perf probe -L getname_flags 2>&1 | egrep 'result.*=.*filename;' | sed -r 's/[[:space:]]+([[:digit:]]+)[[:space:]]+result->uptr.*/\1/') perf probe -q "vfs_getname=getname_flags:${line} pathname=result->name:string" || \ - perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:string" + perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:ustring" fi }