linux-kernel - Re: [PATCH v5] x86: Enable fast strings on Intel if BIOS hasn't already

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Message-ID: <518145F6.3060800@zytor.com>
Date:	Wed, 01 May 2013 09:42:30 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Theodore Ts'o" <tytso@....edu>, Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Andrew Lutomirski <luto@....edu>
Subject: Re: [PATCH v5] x86: Enable fast strings on Intel if BIOS hasn't already

On 05/01/2013 09:34 AM, Theodore Ts'o wrote:
> 
> In fact, there is the question of whether we should be checking to see
> if the CPU stepping is one of the ones with the bug, and if so, to
> have Linux disable fast strings even if the BIOS didn't, instead of
> blindly enabling fast strings....
> 

The erratum reads seriously, but it only affects crossings between pages
of different page types, which is rare in itself.  WT and WP are not
even used in Linux; the UC case we end up doing 8-byte stores instead of
the proper size, which is wrong, but for the case where the user is
malicious the user could just do that directly, and it seems extremely
hard to envision a scenario where someone would do that intentionally.

	-hpa

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