From: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: acme@kernel.org, jolsa@redhat.com, linux-kernel@vger.kernel.org,
aneesh.kumar@linux.ibm.com,
Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Subject: Re: [PATCH] perf probe: Provide more detail with relocation warning
Date: Wed, 26 May 2021 10:23:18 +0530 [thread overview]
Message-ID: <05e32c82-1009-03ba-d973-8b1bc0582ce2@linux.ibm.com> (raw)
In-Reply-To: <20210525214858.33a66846ac09e499c3268a63@kernel.org>
On 5/25/21 6:18 PM, Masami Hiramatsu wrote:
> On Tue, 25 May 2021 10:07:44 +0530
> Ravi Bangoria <ravi.bangoria@linux.ibm.com> wrote:
>
>> When run as normal user with default sysctl kernel.kptr_restrict=0
>> and kernel.perf_event_paranoid=2, perf probe fails with:
>>
>> $ ./perf probe move_page_tables
>> Relocated base symbol is not found!
>>
>> The warning message is not much informative. The reason perf fails
>> is because /proc/kallsyms is restricted by perf_event_paranoid=2
>> for normal user and thus perf fails to read relocated address of
>> the base symbol.
>>
>> Tweaking kptr_restrict and perf_event_paranoid can change the
>> behavior of perf probe. Also, running as root or privileged user
>> works too. Add these details in the warning message.
>>
>> Plus, kmap->ref_reloc_sym might not be always set even if
>> host_machine is initialized. Above is the example of the same.
>> Remove that comment.
>
> Yes, those are restricted in some cases. Anyway without priviledged
> (super) user, perf probe can not set the probe in ftrace.
>
> Hmm, I think it should check the effective user-id at first. If it
> is not super user and the action will access tracefs and kallsyms,
> it should warn at that point.
If kptr_restrict=2, perf probe fails with same error even for root user.
That's why I thought to just change this warning message.
Different combinations of privilege, perf_event_paranoid, kptr_restrict:
Normal/Root user
| perf_event_paranoid
V V kptr_restrict perf probe error
----------------------------------------------------------------
N -1 0 Failed to open kprobe_events: Permission denied
N 0 0 Failed to open kprobe_events: Permission denied
N 1 0 Failed to open kprobe_events: Permission denied
N 2 0 Relocated base symbol is not found!
N -1 1 Relocated base symbol is not found!
N 0 1 Relocated base symbol is not found!
N 1 1 Relocated base symbol is not found!
N 2 1 Relocated base symbol is not found!
N -1 2 Relocated base symbol is not found!
N 0 2 Relocated base symbol is not found!
N 1 2 Relocated base symbol is not found!
N 2 2 Relocated base symbol is not found!
R -1 0 No error.
R 0 0 No error.
R 1 0 No error.
R 2 0 No error.
R -1 1 No error.
R 0 1 No error.
R 1 1 No error.
R 2 1 No error.
R -1 2 Relocated base symbol is not found!
R 0 2 Relocated base symbol is not found!
R 1 2 Relocated base symbol is not found!
R 2 2 Relocated base symbol is not found!
Ravi
next prev parent reply other threads:[~2021-05-26 4:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-25 4:37 [PATCH] perf probe: Provide more detail with relocation warning Ravi Bangoria
2021-05-25 12:48 ` Masami Hiramatsu
2021-05-26 4:53 ` Ravi Bangoria [this message]
2021-05-26 6:33 ` Masami Hiramatsu
2021-05-26 12:56 ` Arnaldo Carvalho de Melo
2021-05-26 14:20 ` Masami Hiramatsu
2021-06-02 11:52 ` Arnaldo Carvalho de Melo
2021-06-02 12:12 ` Masami Hiramatsu
2021-06-02 13:15 ` Arnaldo Carvalho de Melo
2021-05-26 9:01 ` [PATCH] tools/perf: doc: Add permission and sysctl notice Masami Hiramatsu
2021-05-26 9:50 ` Ravi Bangoria
2021-05-26 13:16 ` Masami Hiramatsu
2021-05-26 14:51 ` [PATCH v2] " Masami Hiramatsu
2021-06-02 11:53 ` Arnaldo Carvalho de Melo
2021-06-02 13:51 ` Ravi Bangoria
2021-06-04 13:25 ` Arnaldo Carvalho de Melo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=05e32c82-1009-03ba-d973-8b1bc0582ce2@linux.ibm.com \
--to=ravi.bangoria@linux.ibm.com \
--cc=acme@kernel.org \
--cc=aneesh.kumar@linux.ibm.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mhiramat@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).