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From: Nick Desaulniers <ndesaulniers@google.com>
To: David Laight <David.Laight@aculab.com>
Cc: Christoph Hellwig <hch@lst.de>,
	David Hildenbrand <david@redhat.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"kernel-team@android.com" <kernel-team@android.com>,
	Andrew Morton <akpm@linux-foundation.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: Thu, 22 Oct 2020 10:54:06 -0700
Message-ID: <CAKwvOdnix6YGFhsmT_mY8ORNPTOsN3HwS33Dr0Ykn-pyJ6e-Bw@mail.gmail.com> (raw)
In-Reply-To: <8f1fff0c358b4b669d51cc80098dbba1@AcuMS.aculab.com>


[-- Attachment #1: Type: text/plain, Size: 2086 bytes --]

On Thu, Oct 22, 2020 at 9:35 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Christoph Hellwig
> > Sent: 22 October 2020 14:24
> >
> > On Thu, Oct 22, 2020 at 11:36:40AM +0200, David Hildenbrand wrote:
> > > My thinking: if the compiler that calls import_iovec() has garbage in
> > > the upper 32 bit
> > >
> > > a) gcc will zero it out and not rely on it being zero.
> > > b) clang will not zero it out, assuming it is zero.
> > >
> > > But
> > >
> > > a) will zero it out when calling the !inlined variant
> > > b) clang will zero it out when calling the !inlined variant
> > >
> > > When inlining, b) strikes. We access garbage. That would mean that we
> > > have calling code that's not generated by clang/gcc IIUC.
> >
> > Most callchains of import_iovec start with the assembly syscall wrappers.
>
> Wait...
> readv(2) defines:
>         ssize_t readv(int fd, const struct iovec *iov, int iovcnt);
>
> But the syscall is defined as:
>
> SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
>                 unsigned long, vlen)
> {
>         return do_readv(fd, vec, vlen, 0);
> }
>
> I'm guessing that nothing actually masks the high bits that come
> from an application that is compiled with clang?
>
> The vlen is 'unsigned long' through the first few calls.
> So unless there is a non-inlined function than takes vlen
> as 'int' the high garbage bits from userspace are kept.

Yeah, that's likely a bug: https://godbolt.org/z/KfsPKs

>
> Which makes it a bug in the kernel C syscall wrappers.
> They need to explicitly mask the high bits of 32bit
> arguments on arm64 but not x86-64.

Why not x86-64? Wouldn't it be *any* LP64 ISA?

Attaching a patch that uses the proper width, but I'm pretty sure
there's still a signedness issue .  Greg, would you mind running this
through the wringer?

>
> What does the ARM EABI say about register parameters?

AAPCS is the ABI for 64b ARM, IIUC, which is the ISA GKH is reporting
the problem against. IIUC, EABI is one of the 32b ABIs.  aarch64 is
LP64 just like x86_64.

--
Thanks,
~Nick Desaulniers

[-- Attachment #2: 0001-fs-fix-up-type-confusion-in-readv-writev.patch --]
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  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 [this message]
     [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
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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