linux-kernel - Re: [PATCH] x86: do not overrun page table ranges in gup

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: <87prox5x3t.fsf@saeurebad.de>
Date:	Tue, 29 Jul 2008 02:53:58 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, akpm@...uxfoundation.org,
	torvalds@...uxfoundation.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: do not overrun page table ranges in gup

Hi,

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Tue, 29 Jul 2008, Johannes Weiner wrote:
>> 
>> Actually, I think the prettier fix would be to just establish that
>> garuantee:
>>
>> --- a/arch/x86/mm/gup.c
>> +++ b/arch/x86/mm/gup.c
>> @@ -223,7 +223,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
>>  			struct page **pages)
>>  {
>>  	struct mm_struct *mm = current->mm;
>> -	unsigned long end = start + (nr_pages << PAGE_SHIFT);
>> +	unsigned long end = PAGE_ALIGN(start + (nr_pages << PAGE_SHIFT));
>
> Umm. 'end' is guaranteed to be page-aligned if 'start' is. 
>
> So if this makes a difference, that implies that _start_ isn't 
> page-aligned, and then you when you add PAGE_SIZE to 'addr', you are going 
> to miss 'end' again.
>
> So no, the right fix would be to align 'start' first, which means that 
> everything else (including 'end') will be page-aligned. Aligning just one 
> or the other is very very wrong.

Blah, I just should call it a day.  Thanks for the explanation, you are
right.

	Hannes
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/