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Date: Sun, 14 Apr 2024 03:18:30 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger@dilger.ca>, Nam Cao <namcao@linutronix.de>,
	=?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-riscv@lists.infradead.org,
	Ext4 Developers List <linux-ext4@vger.kernel.org>,
	Conor Dooley <conor@kernel.org>
Subject: Re: riscv32 EXT4 splat, 6.8 regression?
Message-ID: <20240414021830.GR2118490@ZenIV>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Sat, Apr 13, 2024 at 10:04:57PM -0400, Theodore Ts'o wrote:
> On Sat, Apr 13, 2024 at 07:46:03PM -0600, Andreas Dilger wrote:
> > This looks like a straight-forward mathematical substitution of "dlimit"
> > with "search_buf + buf_size" and rearranging of the terms to make the
> > while loop offset "zero based" rather than "address based" and would
> > avoid overflow if "search_buf" was within one 4kB block of overflow:
> > 
> >    dlimit = search_buf + buf_size = 0xfffff000 + 0x1000 = 0x00000000
> 
> Umm... maybe, but does riscv32 actually have a memory map where a
> kernel page would actually have an address in high memory like that?
> That seems.... unusual.

Would instanty break IS_ERR() and friends.  And those are arch-independent.