linux-kernel - Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4F74E5B8.7050905@zytor.com>
Date:	Thu, 29 Mar 2012 15:44:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Sharp <dhsharp@...gle.com>
CC:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Justin Teravest <teravest@...gle.com>,
	Laurent Chavey <chavey@...gle.com>,
	Michael Davidson <md@...gle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace
 handler

On 03/29/2012 03:40 PM, David Sharp wrote:
> On Thu, Mar 29, 2012 at 1:06 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> I had a long discussion with Frederic over IRC earlier today.  We came
>> up with the following strawman:
>>
>> 1. A system call thunk (which could be enabled/disabled by patching the
>> syscall table.)  This provides an entry and exit hook, and also sets a
>> per-thread flag to capture userspace traffic.
> 
> Our goal is for syscall traces to be as fast as regular tracepoints.
> iirc, What we've found is that much of the extra overhead of syscall
> tracepoints as compared to regular tracepoints is due to that the code
> path for syscall tracing is bundled with checks for ptrace and other
> stuff (Vaibhav did all this characterization, he can jump in with
> details if wanted). How much work would this "thunk" have to do that
> is not either recording the trace or calling the syscall?

Nothing.  That IS what the thunk would do:

thunk:
	<record syscall entry>
	call real_syscall_table(syscall_number)
	<record syscall exit>
	ret

	-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/