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From: Peter Mamonov <pmamonov@gmail.com>
To: Lucas Stach <l.stach@pengutronix.de>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH] commands: mem: truncate mem device size to fit the loff_t file size
Date: Wed, 7 Nov 2018 20:07:22 +0300	[thread overview]
Message-ID: <20181107170721.yelfwfusdnovybr7@localhost.localdomain> (raw)
In-Reply-To: <1541606897.2508.55.camel@pengutronix.de>

On Wed, Nov 07, 2018 at 05:08:17PM +0100, Lucas Stach wrote:
> Am Mittwoch, den 07.11.2018, 16:45 +0300 schrieb Peter Mamonov:
> > Hi, Lucas,
> > 
> > On Tue, Nov 06, 2018 at 05:14:07PM +0100, Lucas Stach wrote:
> > > On 64bit arches the file covering the whole address space is larger than
> > > what can be represented in the loff_t type (s64) used for the file size.
> > > Thus the size of this device is interpreted as negative in a lot of
> > > places. Fix this by truncating the size to fit the file size type.
> > 
> > While this is probably an appropriate solution for some architectures, it will 
> > cause problems on MIPS64. The root of evil is MIPS64 address space 
> > segmentation: https://docplayer.net/docs-images/25/4553906/images/21-0.png).  
> > Most notably your patch prevents access to the xkphys segment, where most 
> > peripheral devices of a SoC are accessible.
> 
> Isn't this a problem for MIPS64 even before my patch? For example the
> "mw" command uses open_and_lseek on the dev/mem file with the address
> of the write being the seek offset. As this is a loff_t value, seeking
> to something with the highest order bit set won't do what you expect to
> happen, right?

You are right. I fixed this in a straightforward manner (see the patch 
below). Guess it's time to find a better solution :)

	Author: Peter Mamonov <pmamonov@gmail.com>
	Date:   Thu Jul 6 13:32:53 2017 +0300
	
	    FIXME: fs: fix memory access for 64bit MIPS
	
	diff --git a/fs/fs.c b/fs/fs.c
	index f61ee091b5..45190812c5 100644
	--- a/fs/fs.c
	+++ b/fs/fs.c
	@@ -941,8 +941,6 @@ loff_t lseek(int fildes, loff_t offset, int whence)
		case SEEK_SET:
			if (f->size != FILE_SIZE_STREAM && offset > f->size)
				goto out;
	-               if (offset < 0)
	-                       goto out;
			pos = offset;
			break;
		case SEEK_CUR:
	@@ -960,10 +958,6 @@ loff_t lseek(int fildes, loff_t offset, int whence)
		}
	        
		pos = fsdrv->lseek(&f->fsdev->dev, f, pos);
	-       if (pos < 0) {
	-               errno = -pos;
	-               return -1;
	-       }
	        
		return pos;

Regards,
Peter

> 
> Regards,
> Lucas

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      reply	other threads:[~2018-11-07 17:07 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-06 16:14 Lucas Stach
2018-11-07  7:47 ` Sascha Hauer
2018-11-07 13:45 ` Peter Mamonov
2018-11-07 16:08   ` Lucas Stach
2018-11-07 17:07     ` Peter Mamonov [this message]

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