lkml.org 
[lkml]   [2020]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3] perf test: Fix test trace+probe_vfs_getname.sh
From
Date
On 2/14/20 1:45 AM, Masami Hiramatsu wrote:
> On Thu, 13 Feb 2020 15:11:40 -0300
> Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
>
>> Em Fri, Feb 14, 2020 at 02:01:51AM +0900, Masami Hiramatsu escreveu:
>>> On Thu, 13 Feb 2020 11:30:48 -0300 Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
>>
>>>> Em Thu, Feb 13, 2020 at 01:20:09PM +0100, Thomas Richter escreveu:
>>>>> 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)
>>
>>>>> Variable filename 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.
>>
>>>>> The following patch specifies user space memory access first and if this
>>>>> fails use type 'string' in case 'ustring' is not supported.
>>
>>>> What are you fixing?
>>
>>>> I haven't seen any example of this test failing, and right now testing
>>>> it with:
>>
>>>> [root@quaco ~]# uname -a
>>>> Linux quaco 5.6.0-rc1+ #1 SMP Wed Feb 12 15:42:16 -03 2020 x86_64 x86_64 x86_64 GNU/Linux
>>>> [root@quaco ~]#
>>
>>> This bug doesn't happen on x86 or other archs on which user-address space and
>>> kernel address space is same. On some arch (ppc64 in this case?) user-address
>>> space is partially or completely 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 spaces. That is why I introduced "ustring" type
>>> for kprobe event.
>>> As far as I can see, Thomas's patch is sane.
>>
>> Well, without his patch, on x86, the test he is claiming to be fixing
>> works well, with his patch it stops working, see the rest of my reply.
>
> OK, let me see.
>
>
>> diff --git a/tools/perf/tests/shell/lib/probe_vfs_getname.sh b/tools/perf/tests/shell/lib/probe_vfs_getname.sh
>> index 7cb99b433888..30c1eadbc5be 100644
>> --- a/tools/perf/tests/shell/lib/probe_vfs_getname.sh
>> +++ b/tools/perf/tests/shell/lib/probe_vfs_getname.sh
>> @@ -13,7 +13,9 @@ add_probe_vfs_getname() {
>> local verbose=$1
>> 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:${line} pathname=result->name:string" || \
>> + perf probe -q "vfs_getname=getname_flags:${line} pathname=result->uptr:ustring" || \
>> + perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:ustring" || \
>> + perf probe -q "vfs_getname=getname_flags:${line} pathname=result->uptr:string" || \
>> perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:string"
>> fi
>> }
>
> This looks no good (depends on architecture or debuginfo). In fs/namei.c,
>
> struct filename *
> getname_flags(const char __user *filename, int flags, int *empty)
> ...
> kname = (char *)result->iname;
> result->name = kname;
> ...
> result->uptr = filename;
> result->aname = NULL;
> audit_getname(result);
> return result;
> }
>
> And the line number script, egreps below line.
>
> result->uptr = filename;
>
> However, the probe on this line will hit *before* execute this line.
> Note that kprobes is a breakpoint, which breaks into this line execution,
> not after executed.
>
> So, I thik at this point, result->uptr should be NULL, but filename and
> result->name already have assigned value.
>
> Thus, the fix should be something like below.
>
>> 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" || \
>
> Thomas, is this OK for you too, or would you have any reason to trace
> result->uptr?
>
> Thank you,
>

Thank you very much for your help!!!

I started from scratch and just installed linux 5.6.0rc1 without
any changes and got this failure:

[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]#

Now I applied Masami's patch and this is the result

[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

Can we commit this patch?
Thanks a lot
--
Thomas Richter, Dept 3252, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzender des Aufsichtsrats: Matthias Hartmann
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294

\
 
 \ /
  Last update: 2020-02-14 10:44    [W:0.080 / U:0.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site