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From: David Hildenbrand <david@redhat.com>
To: Al Viro <viro@zeniv.linux.org.uk>,
	Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	David Laight <David.Laight@aculab.com>,
	Christoph Hellwig <hch@lst.de>,
	Greg KH <gregkh@linuxfoundation.org>,
	"kernel-team@android.com" <kernel-team@android.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, David Howells <dhowells@redhat.com>,
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	<linux-arm-kernel@lists.infradead.org>,
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Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"
Date: Fri, 23 Oct 2020 15:12:23 +0200
Message-ID: <e7a8f709-87b8-c328-6190-8371c6fa3ae8@redhat.com> (raw)
In-Reply-To: <20201022192458.GV3576660@ZenIV.linux.org.uk>

On 22.10.20 21:24, Al Viro wrote:
> On Thu, Oct 22, 2020 at 12:04:52PM -0700, Nick Desaulniers wrote:
> 
>> Passing an `unsigned long` as an `unsigned int` does no such
>> narrowing: https://godbolt.org/z/TvfMxe (same vice-versa, just tail
>> calls, no masking instructions).
>> So if rw_copy_check_uvector() is inlined into import_iovec() (looking
>> at the mainline@1028ae406999), then children calls of
>> `rw_copy_check_uvector()` will be interpreting the `nr_segs` register
>> unmodified, ie. garbage in the upper 32b.
> 
> FWIW,
> 
> void f(unsinged long v)
> {
> 	if (v != 1)
> 		printf("failed\n");
> }
> 
> void g(unsigned int v)
> {
> 	f(v);
> }
> 
> void h(unsigned long v)
> {
> 	g(v);
> }
> 
> main()
> {
> 	h(0x100000001);
> }
> 
> must not produce any output on a host with 32bit int and 64bit long, regardless of
> the inlining, having functions live in different compilation units, etc.
> 
> Depending upon the calling conventions, compiler might do truncation in caller or
> in a callee, but it must be done _somewhere_.

The interesting case is having g() in a separate compilation unit and
force-calling g() with 0x100000001 via inline ASM. So forcing garbage
into high bits.

I'll paly with it.

-- 
Thanks,

David / dhildenb


  parent reply index

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-25  4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25  4:51 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-25  4:51 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-10-21 16:13   ` Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c" Greg KH
2020-10-21 20:59     ` David Laight
2020-10-21 23:39     ` Al Viro
2020-10-22  8:26       ` Greg KH
2020-10-22  8:35         ` David Hildenbrand
2020-10-22  8:40           ` David Laight
2020-10-22  8:48             ` David Hildenbrand
2020-10-22  9:01               ` Greg KH
2020-10-22  9:06                 ` David Laight
2020-10-22  9:19                 ` David Hildenbrand
2020-10-22  9:25                   ` David Hildenbrand
2020-10-22  9:32                     ` David Laight
2020-10-22  9:36                       ` David Hildenbrand
2020-10-22 10:48                         ` Greg KH
2020-10-22 12:18                           ` Greg KH
2020-10-22 12:42                             ` David Hildenbrand
2020-10-22 12:57                               ` Greg KH
2020-10-22 13:50                                 ` Greg KH
     [not found]                                   ` <CAK8P3a1B7OVdyzW0-97JwzZiwp0D0fnSfyete16QTvPp_1m07A@mail.gmail.com>
2020-10-22 14:40                                     ` Greg KH
2020-10-22 16:15                                       ` David Laight
2020-10-23 12:46                                   ` David Laight
2020-10-23 13:09                                     ` David Hildenbrand
2020-10-23 14:33                                       ` David Hildenbrand
2020-10-23 14:39                                         ` David Laight
2020-10-23 14:47                                           ` 'Greg KH'
2020-10-23 16:33                                             ` David Hildenbrand
2020-11-02  9:06                                             ` David Laight
2020-11-02 13:52                                               ` 'Greg KH'
2020-11-02 18:23                                                 ` David Laight
2020-10-23 17:58                                       ` Al Viro
2020-10-23 18:27                                         ` Segher Boessenkool
2020-10-23 21:28                                           ` David Laight
2020-10-24 17:29                                             ` Segher Boessenkool
2020-10-24 21:12                                               ` David Laight
     [not found]                                     ` <CAK8P3a1n+b8hOMhNQSDzgic03dyXbmpccfTJ3C1bGKvzsgMXbg@mail.gmail.com>
2020-10-23 13:28                                       ` David Laight
2020-10-22 13:23                         ` Christoph Hellwig
2020-10-22 16:35                           ` David Laight
2020-10-22 16:40                             ` Matthew Wilcox
2020-10-22 16:50                               ` David Laight
2020-10-22 17:00                               ` Nick Desaulniers
2020-10-22 20:59                                 ` Eric Biggers
2020-10-22 21:28                                   ` Al Viro
2020-10-22 18:19                               ` Al Viro
2020-10-22 17:54                             ` Nick Desaulniers
     [not found]                               ` <CAK8P3a3LjG+ZvmQrkb9zpgov8xBkQQWrkHBPgjfYSqBKGrwT4w@mail.gmail.com>
2020-10-22 19:04                                 ` Nick Desaulniers
2020-10-22 19:24                                   ` Al Viro
2020-10-22 19:27                                     ` Al Viro
2020-10-22 20:06                                     ` Al Viro
2020-10-22 20:09                                       ` Al Viro
2020-10-22 20:11                                     ` Nick Desaulniers
2020-10-22 22:07                                     ` David Laight
2020-10-23 13:12                                     ` David Hildenbrand [this message]
2020-10-22 22:04                                   ` David Laight
2020-10-22  9:28                   ` David Laight
2020-10-22  9:02               ` David Laight
2020-09-25  4:51 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-25  4:51 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-25  4:51 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-25  4:51 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-25  4:51 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-25  4:51 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-25  4:51 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
2020-09-25 15:23 ` let import_iovec deal with compat_iovecs as well v4 Al Viro

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