linux-kernel - Re: [PATCH v2] x86/boot: Rename overlapping memcpy() to memmove()

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Message-ID: <CAGXu5jJb1KKDfYsZPPGrF-1UUf1sKkvzdt=i115bKKhOBp72Vw@mail.gmail.com>
Date:	Thu, 28 Apr 2016 09:49:18 -0700
From:	Kees Cook <keescook@...omium.org>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Ingo Molnar <mingo@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
	Baoquan He <bhe@...hat.com>, Borislav Petkov <bp@...e.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86/boot: Rename overlapping memcpy() to memmove()

On Thu, Apr 28, 2016 at 9:47 AM, One Thousand Gnomes
<gnomes@...rguk.ukuu.org.uk> wrote:
> O> For example, this is what I've got currently:
>>
>> /* Detect and warn about potential overlaps. */
>> void *memcpy(void *dest, const void *src, size_t n)
>> {
>>         if (dest > src && dest - src < n)
>>                 warn("Potentially unsafe overlapping memcpy detected!");
>>         return __memcpy(dest, src, n);
>> }
>>
>> Does that seem okay? If so, I'll send the patch...
>
> Probably useful for debug, but instead of relying on __memcpy
> happening to handle overlaps - which isn't portable you could instead
> debug all platforms by doing
>
>         if (...) {
>                 warn(...)
>                 memmove()
>         } else
>                 __memcpy
>

Yeah, that's kind of where we started (but without the warning). I
prefer this, since we don't run the risk of MAYBE breaking. We warn,
but we remain safe.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security