From: Sven Schnelle <svens@linux.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tracing: fix memcpy size when copying stack entries
Date: Tue, 13 Jun 2023 07:19:14 +0200 [thread overview]
Message-ID: <yt9dy1koey7h.fsf@linux.ibm.com> (raw)
In-Reply-To: <20230612123407.5ebcabdf@gandalf.local.home> (Steven Rostedt's message of "Mon, 12 Jun 2023 12:34:07 -0400")
Steven Rostedt <rostedt@goodmis.org> writes:
> On Mon, 12 Jun 2023 18:07:48 +0200
> Sven Schnelle <svens@linux.ibm.com> wrote:
>
>> Noticed the following warning during boot:
>>
>> [ 2.316341] Testing tracer wakeup:
>> [ 2.383512] ------------[ cut here ]------------
>> [ 2.383517] memcpy: detected field-spanning write (size 104) of single field "&entry->caller" at kernel/trace/trace.c:3167 (size 64)
>>
>> The reason seems to be that the maximum number of entries is calculated
>> from the size of the fstack->calls array which is 128. But later the same
>> size is used to memcpy() the entries to entry->callers, which has only
>> room for eight elements. Therefore use the minimum of both arrays as limit.
>>
>> Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
>> ---
>> kernel/trace/trace.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 64a4dde073ef..988d664c13ec 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -3146,7 +3146,7 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer,
>> barrier();
>>
>> fstack = this_cpu_ptr(ftrace_stacks.stacks) + stackidx;
>> - size = ARRAY_SIZE(fstack->calls);
>> + size = min(ARRAY_SIZE(entry->caller), ARRAY_SIZE(fstack->calls));
>
> No, this is not how it works, and this breaks the stack tracing code.
> [..]
> The old way use to just record the 8 entries, but that was not very useful
> in real world analysis. Your patch takes that away. Might as well just
> record directly into the ring buffer again like it use to.
>
> Yes the above may be special, but your patch breaks it.
Indeed, i'm feeling a bit stupid for sending that patch, should have
used my brain during reading the source. Thanks for the explanation.
next prev parent reply other threads:[~2023-06-13 5:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-12 16:07 [PATCH] tracing: fix memcpy size when copying stack entries Sven Schnelle
2023-06-12 16:34 ` Steven Rostedt
2023-06-13 5:19 ` Sven Schnelle [this message]
2023-06-13 15:37 ` Steven Rostedt
2023-06-14 10:41 ` Sven Schnelle
2023-06-14 11:30 ` David Laight
2023-07-12 14:06 ` Sven Schnelle
2023-07-12 14:14 ` Steven Rostedt
2023-07-12 14:26 ` Steven Rostedt
2023-07-12 14:32 ` Sven Schnelle
2023-07-12 14:31 ` Sven Schnelle
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=yt9dy1koey7h.fsf@linux.ibm.com \
--to=svens@linux.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=rostedt@goodmis.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).