linux-kernel - Re: bisected boot regression post 2.6.25-rc3.. please revert

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Message-ID: <18388.47773.77106.664217@cargo.ozlabs.ibm.com>
Date:	Mon, 10 Mar 2008 15:35:41 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	hans.rosenfeld@....com, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: bisected boot regression post 2.6.25-rc3.. please revert

Linus Torvalds writes:

> But even for PAGE_MASK, we literally have code like this:
> 
> 	if ((size_avail & PAGE_MASK) < rg.size) {
> 
> where it so _happens_ that "size_avail" is unsigned, but what if it 
> wasn't? It could turn a unsigned comparison into a signed one, and 
> introduce any number of security bugs etc.

We have had PAGE_MASK being signed on powerpc for ages, so if you do
find any such bugs, please let me know. :)  I'm not aware of any at
present, though.

The expression you quoted will be ok as long as either size_avail or
rg.size is unsigned, as far as I can see.

Our PAGE_SIZE is unsigned long.

Paul.
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