linux-kernel - Re: [PATCH] mm/tlb: Fix use

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: <6A09F721-0AD9-4B86-AB3E-563A1CF5ABDE@amacapital.net>
Date:   Fri, 21 Feb 2020 11:22:16 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH] mm/tlb: Fix use_mm() vs TLB invalidate



> On Feb 21, 2020, at 11:19 AM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> On Fri, Feb 21, 2020 at 3:11 AM Peter Zijlstra <peterz@...radead.org> wrote:
>> 
>> +       BUG_ON(!(tsk->flags & PF_KTHREAD));
>> +       BUG_ON(tsk->mm != NULL);
> 
> Stop this craziness.
> 
> There is absolutely ZERO excuse for this kind of garbage.
> 
> Making this a BUG_ON() will just cause all the possible debugging info
> to be thrown away and lost, and you often have a dead machine.
> 
> For absolutely no good reason.
> 
> Make it a WARN_ON_ONCE(). If it triggers, everything works the way it
> always did, but we get notified.
> 
> Stop with the stupid crazy BUG_ON() crap already. It is actively _bad_
> for debugging.
> 
>  

In this particular case, if we actually flub this, we are very likely to cause data corruption — we’re about to do user access with the wrong mm.

So I suppose we could switch to init_mm and carry on. *Something* will crash, but it probably won’t corrupt data or take down the machine.