linux-kernel - Re: [PATCH v2 06/20] x86/alternative: use temporary mm for text poking

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Message-ID: <6D321F51-6B19-46F6-91AC-74248A542BA0@vmware.com>
Date:   Tue, 5 Feb 2019 17:54:56 +0000
From:   Nadav Amit <namit@...are.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Damian Tometzki <linux_dti@...oud.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux-MM <linux-mm@...ck.org>, Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        "Dock, Deneen T" <deneen.t.dock@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2 06/20] x86/alternative: use temporary mm for text
 poking

> On Feb 5, 2019, at 4:35 AM, Borislav Petkov <bp@...en8.de> wrote:
> 
> On Tue, Feb 05, 2019 at 12:31:46PM +0100, Peter Zijlstra wrote:
>> ...
>> 
>> So while in general I agree with BUG_ON() being undesirable, I think
>> liberal sprinking in text_poke() is fine; you really _REALLY_ want this
>> to work or fail loudly. Text corruption is just painful.
> 
> Ok. It would be good to have the gist of this sentiment in a comment
> above it so that it is absolutely clear why we're doing it.

I added a short comment for v3 above each BUG_ON().

> And since text_poke() can't fail, then it doesn't need a retval too.
> AFAICT, nothing is actually using it.

As Peter said, this is addressed in a separate patch (one patch per logical
change).