From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
live-patching@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Konstantin Khorenko <khorenko@virtuozzo.com>
Subject: Re: 'perf probe' and symbols from .text.<something>
Date: Mon, 22 Feb 2021 11:51:50 -0600 [thread overview]
Message-ID: <20210222175150.yxgw3sxxaqjqgq56@treble> (raw)
In-Reply-To: <20210223000508.cab3cddaa3a3790525f49247@kernel.org>
On Tue, Feb 23, 2021 at 12:05:08AM +0900, Masami Hiramatsu wrote:
> > Of course, one could place probes using absolute addresses of the
> > functions but that would be less convenient.
> >
> > This also affects many livepatch modules where the kernel code can be
> > compiled with -ffunction-sections and each function may end up in a
> > separate section .text.<function_name>. 'perf probe' cannot be used
> > there, except with the absolute addresses.
> >
> > Moreover, if FGKASLR patches are merged
> > (https://lwn.net/Articles/832434/) and the kernel is built with FGKASLR
> > enabled, -ffunction-sections will be used too. 'perf probe' will be
> > unable to see the kernel functions then.
>
> Hmm, if the FGKASLAR really randomizes the symbol address, perf-probe
> should give up "_text-relative" probe for that kernel, and must fallback
> to the "symbol-based" probe. (Are there any way to check the FGKASLR is on?)
> The problem of "symbol-based" probe is that local (static) symbols
> may share a same name sometimes. In that case, it can not find correct
> symbol. (Maybe I can find a candidate from its size.)
> Anyway, sometimes the security and usability are trade-off.
We had a similar issue with FGKASLR and live patching. The proposed
solution is a new linker flag which eliminates duplicates: -z
unique-symbol.
https://sourceware.org/bugzilla/show_bug.cgi?id=26391
--
Josh
next prev parent reply other threads:[~2021-02-22 17:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 17:09 'perf probe' and symbols from .text.<something> Evgenii Shatokhin
2021-02-18 19:35 ` Josh Poimboeuf
2021-02-22 15:05 ` Masami Hiramatsu
2021-02-22 15:12 ` Masami Hiramatsu
2021-02-22 17:51 ` Josh Poimboeuf [this message]
2021-02-23 1:23 ` Masami Hiramatsu
2021-02-23 7:36 ` Masami Hiramatsu
2021-02-23 19:45 ` Josh Poimboeuf
2021-02-24 8:00 ` Masami Hiramatsu
2021-02-23 1:48 ` [PATCH] perf-probe: Failback to symbol-base probe for probes on module Masami Hiramatsu
2021-02-23 7:36 ` Masami Hiramatsu
2021-02-23 7:09 ` 'perf probe' and symbols from .text.<something> Masami Hiramatsu
2021-02-23 7:37 ` [PATCH] perf-probe: dso: Add symbols in .text.* subsections to text symbol map in kenrel modules Masami Hiramatsu
2021-02-23 15:02 ` Evgenii Shatokhin
2021-02-23 20:11 ` Arnaldo Carvalho de Melo
2021-02-24 7:47 ` Evgenii Shatokhin
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=20210222175150.yxgw3sxxaqjqgq56@treble \
--to=jpoimboe@redhat.com \
--cc=acme@kernel.org \
--cc=eshatokhin@virtuozzo.com \
--cc=khorenko@virtuozzo.com \
--cc=kristen@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=live-patching@vger.kernel.org \
--cc=mhiramat@kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.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).