linux-kernel - Re: [PATCH 01/17] Fix "x86/alternatives: Lockdep-enforce text_mutex in text

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Date:   Fri, 25 Jan 2019 18:28:04 +0000
From:   Nadav Amit <namit@...are.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     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>,
        Peter Zijlstra <peterz@...radead.org>,
        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@...ux.intel.com" <kristen@...ux.intel.com>,
        "deneen.t.dock@...el.com" <deneen.t.dock@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 01/17] Fix "x86/alternatives: Lockdep-enforce text_mutex
 in text_poke*()"

> On Jan 25, 2019, at 1:30 AM, Borislav Petkov <bp@...en8.de> wrote:
> 
> On Wed, Jan 16, 2019 at 04:32:43PM -0800, Rick Edgecombe wrote:
>> From: Nadav Amit <namit@...are.com>
>> 
>> text_mutex is currently expected to be held before text_poke() is
>> called, but we kgdb does not take the mutex, and instead *supposedly*
>> ensures the lock is not taken and will not be acquired by any other core
>> while text_poke() is running.
>> 
>> The reason for the "supposedly" comment is that it is not entirely clear
>> that this would be the case if gdb_do_roundup is zero.
> 
> I guess that variable name is "kgdb_do_roundup” ?

Yes. Will fix.

> 
>> This patch creates two wrapper functions, text_poke() and
> 
> Avoid having "This patch" or "This commit" in the commit message. It is
> tautologically useless.
> 
> Also, do
> 
> $ git grep 'This patch' Documentation/process
> 
> for more details.

Ok.

>> 
>> +void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
> 
> text_poke_unlocked() I guess. I don't think kgdb is that special that it
> needs its own function flavor.

Tglx suggested this naming to prevent anyone from misusing text_poke_kdgb().
This is a very specific use-case that nobody else should need.

Regards,
Nadav