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

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Message-ID: <BEFCBDFB-F08F-441D-8BCC-07E5F448D9D2@vmware.com>
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

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