linux-kernel - Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

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: <20241029135617.GB14555@noisy.programming.kicks-ass.net>
Date: Tue, 29 Oct 2024 14:56:17 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

On Mon, Oct 28, 2024 at 02:47:38PM -0700, Josh Poimboeuf wrote:

> + * The only exception is when the task has migrated to another CPU, *and* this
> + * is called while the task work is running (or has already run).  Then a new
> + * cookie will be generated and the callback will be called again for the new
> + * cookie.

So that's a bit crap. The user stack won't change for having been
migrated.

So perf can readily use the full u64 cookie value as a sequence number,
since the whole perf record will already have the TID of the task in.
Mixing in this CPU number for no good reason and causing trouble like
this just doesn't make sense to me.

If ftrace needs brain damage like this, can't we push this to the user?

That is, do away with the per-cpu sequence crap, and add a per-task
counter that is incremented for every return-to-userspace.