linux-kernel - Re: [PATCH 1/2] lib: add fast lzo decompressor

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Message-ID: <18900.52255.798522.393088@stoffel.org>
Date:	Thu, 2 Apr 2009 10:30:55 -0400
From:	"John Stoffel" <john@...ffel.org>
To:	Andreas Robinson <andr345@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Alain Knaff <alain@...ff.lu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lib: add fast lzo decompressor

>>>>> "Andreas" == Andreas Robinson <andr345@...il.com> writes:

Andreas> On Wed, 2009-04-01 at 09:12 -0700, H. Peter Anvin wrote:
>> Andreas Robinson wrote:
>> > This patch adds an LZO decompressor tweaked to be faster than
>> > the 'safe' decompressor already in the kernel.
>> > 
>> > On x86_64, it runs in roughly 80% of the time needed by the safe
>> > decompressor.
>> > 
>> > This function is inherently insecure and can cause buffer overruns.
>> > It is only intended for decompressing implicitly trusted data, such
>> > as an initramfs and the kernel itself.
>> > 
>> > As such, the function is neither exported nor declared in a header.
>> > 
>> 
>> OK, I'm more than a bit nervous about that, especially since we're
>> trying to make the decompression functions more generic.

Andreas> Perhaps the system can default to the safe decompressor for
Andreas> normal use and choose the fast one if STATIC is defined or
Andreas> when system_state == SYSTEM_BOOTING?

So how do you prove that data is trusted?  What happens on buffer
overflow?  I don't think that a 20% speedup on decompression, with a
possibility of borking the boot completely is worth it.  Or are you
suggesting that people pre-test their initramfs images with this
compressor before deciding to boot from it?

Reliable booting is better than random crashes in my book.

John
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