From: David Laight <David.Laight@ACULAB.COM>
To: 'Al Viro' <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
David Howells <dhowells@redhat.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-aio@kvack.org" <linux-aio@kvack.org>,
"io-uring@vger.kernel.org" <io-uring@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: RE: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec
Date: Wed, 23 Sep 2020 14:38:24 +0000 [thread overview]
Message-ID: <200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com> (raw)
In-Reply-To: <20200923141654.GJ3421308@ZenIV.linux.org.uk>
From: Al Viro
> Sent: 23 September 2020 15:17
>
> On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote:
>
> > +struct iovec *iovec_from_user(const struct iovec __user *uvec,
> > + unsigned long nr_segs, unsigned long fast_segs,
>
> Hmm... For fast_segs unsigned long had always been ridiculous
> (4G struct iovec on caller stack frame?), but that got me wondering about
> nr_segs and I wish I'd thought of that when introducing import_iovec().
>
> The thing is, import_iovec() takes unsigned int there. Which is fine
> (hell, the maximal value that can be accepted in 1024), except that
> we do pass unsigned long syscall argument to it in some places.
It will make diddly-squit difference.
The parameters end up in registers on most calling conventions.
Plausibly you get an extra 'REX' byte on x86 for the 64bit value.
What you want to avoid is explicit sign/zero extension and value
masking after arithmetic.
On x86-64 the 'horrid' type is actually 'signed int'.
It often needs sign extending to 64bits (eg when being
used as an array subscript).
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-09-23 14:38 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 6:05 let import_iovec deal with compat_iovecs as well v3 Christoph Hellwig
2020-09-23 6:05 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-23 6:05 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-09-23 6:05 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-23 14:16 ` Al Viro
2020-09-23 14:38 ` David Laight [this message]
2020-09-23 14:49 ` Al Viro
2020-09-23 14:40 ` Al Viro
2020-09-23 6:05 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-23 6:05 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-23 14:25 ` Al Viro
2020-09-23 14:32 ` Christoph Hellwig
2020-09-23 14:59 ` Al Viro
2020-09-23 16:38 ` Al Viro
2020-09-23 17:05 ` Al Viro
2020-09-23 17:46 ` Christoph Hellwig
2020-09-23 17:08 ` Brian Gerst
2020-09-23 18:45 ` Arnd Bergmann
2020-09-23 19:47 ` Al Viro
2020-09-23 19:52 ` Arnd Bergmann
2020-09-23 21:30 ` David Laight
2020-09-23 6:05 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-23 6:05 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-23 6:05 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-23 6:05 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
2020-09-25 4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25 4:51 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=200cf2b9ce5e408f8838948fda7ce9a0@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=axboe@kernel.dk \
--cc=dhowells@redhat.com \
--cc=hch@lst.de \
--cc=io-uring@vger.kernel.org \
--cc=keyrings@vger.kernel.org \
--cc=linux-aio@kvack.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-parisc@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=netdev@vger.kernel.org \
--cc=sparclinux@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).