linux-kernel - Re: [PATCH] signal/x86: Delay calling signals in atomic

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: <Ykblv2aKh3ekqpi4@linutronix.de>
Date:   Fri, 1 Apr 2022 13:45:03 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ben Segall <bsegall@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] signal/x86: Delay calling signals in atomic

On 2022-03-30 13:10:05 [-0500], Eric W. Biederman wrote:
> But it looks like if we are coming from userspace then we use the same
> stack as any other time we would come from userspace.  AKA a stack
> that allows the kernel to sleep.
> 
> So I don't see what the problem is that is trying to be fixed.

It is not only the stack. In atomic context / disabled interrupts it is
not possible to acquire a spinlock_t (sighand_struct::siglock) which is
done later.

> I know that code has been changed over the years, perhaps this is
> something that was fixed upstream and the real time tree didn't realize
> there was no longer a need to fix anything?
> 
> Or am I missing something subtle when reading the idtentry assembly?

It certainly is true that the code changed over the years. The per-CPU
stack is one problem, the siglock in atomic context is the other one.
Thank you for the input. Let me digest the informations I have here and
get back.

> Eric

Sebastian