linux-kernel - Re: [PATCH v10 07/14] unwind_user/deferred: Make unwind deferral requests NMI-safe

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: <80DBA3D8-5B52-43DB-8234-EAC51D0FC0E1@goodmis.org>
Date: Thu, 19 Jun 2025 05:42:31 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
CC: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Ingo Molnar <mingo@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>,
 Indu Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>,
 Beau Belgrave <beaub@...ux.microsoft.com>, Jens Remus <jremus@...ux.ibm.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v10 07/14] unwind_user/deferred: Make unwind deferral requests NMI-safe

On June 19, 2025 5:32:26 AM EDT, Peter Zijlstra <peterz@...radead.org> wrote:
>On Thu, Jun 19, 2025 at 05:07:10AM -0400, Steven Rostedt wrote:
>
>> Does #DB make in_nmi() true? If that's the case then we do need to handle that.
>
>Yes: #DF, #MC, #BP (int3), #DB and NMI all have in_nmi() true.
>
>Ignoring #DF because that's mostly game over, you can get them all
>nested for up to 4 (you're well aware of the normal NMI recursion
>crap).

We probably can implement this with stacked counters.

>Then there is the SEV #VC stuff, which is also NMI like. So if you're a
>CoCo-nut, you can perhaps get it up to 5.

The rest of the tracing infrastructure goes 4 deep and hasn't had issues, so 4 is probably sufficient.

-- Steve