From: Andy Lutomirski <luto@kernel.org>
To: NeilBrown <neilb@suse.com>, "Ted Ts'o" <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Peter Zijlstra <peterz@infradead.org>,
Dmitry Safonov <dsafonov@virtuozzo.com>,
Andrew Lutomirski <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>,
Brian Gerst <brgerst@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-tip-commits@vger.kernel.org, jsimmons@infradead.org
Subject: Re: in_compat_syscall() returns from kernel thread for X86_32.
Date: Thu, 18 Oct 2018 10:26:20 -0700 [thread overview]
Message-ID: <CALCETrWH342Y7jKHsYdT=_3fuyDkWhvQLK9z4PTs9jzbfoCVwg@mail.gmail.com> (raw)
In-Reply-To: <871s8ndg6a.fsf@notabene.neil.brown.name>
On Wed, Oct 17, 2018 at 9:36 PM NeilBrown <neilb@suse.com> wrote:
>
> On Wed, Oct 17 2018, Andy Lutomirski wrote:
>
> > On Wed, Oct 17, 2018 at 6:48 PM NeilBrown <neilb@suse.com> wrote:
> >>
> >>
> >> Was: Re: [tip:x86/asm] x86/entry: Rename is_{ia32,x32}_task() to in_{ia32,x32}_syscall()
> >> On Tue, Apr 19 2016, tip-bot for Dmitry Safonov wrote:
> >>
> >> > Commit-ID: abfb9498ee1327f534df92a7ecaea81a85913bae
> >> > Gitweb: http://git.kernel.org/tip/abfb9498ee1327f534df92a7ecaea81a85913bae
> >> > Author: Dmitry Safonov <dsafonov@virtuozzo.com>
> >> > AuthorDate: Mon, 18 Apr 2016 16:43:43 +0300
> >> > Committer: Ingo Molnar <mingo@kernel.org>
> >> > CommitDate: Tue, 19 Apr 2016 10:44:52 +0200
> >> >
> >> > x86/entry: Rename is_{ia32,x32}_task() to in_{ia32,x32}_syscall()
> >> >
> >> ...
> >> > @@ -318,7 +318,7 @@ static inline bool is_x32_task(void)
> >> >
> >> > static inline bool in_compat_syscall(void)
> >> > {
> >> > - return is_ia32_task() || is_x32_task();
> >> > + return in_ia32_syscall() || in_x32_syscall();
> >> > }
> >>
> >> Hi,
> >> I'm reply to this patch largely to make sure I get the right people
> >> .....
> >>
> >> This test is always true when CONFIG_X86_32 is set, as that forces
> >> in_ia32_syscall() to true.
> >> However we might not be in a syscall at all - we might be running a
> >> kernel thread which is always in 64 mode.
> >> Every other implementation of in_compat_syscall() that I found is
> >> dependant on a thread flag or syscall register flag, and so returns
> >> "false" in a kernel thread.
> >>
> >> Might something like this be appropriate?
> >>
> >> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
> >> index 2ff2a30a264f..c265b40a78f2 100644
> >> --- a/arch/x86/include/asm/thread_info.h
> >> +++ b/arch/x86/include/asm/thread_info.h
> >> @@ -219,7 +219,7 @@ static inline int arch_within_stack_frames(const void * const stack,
> >> #ifndef __ASSEMBLY__
> >>
> >> #ifdef CONFIG_X86_32
> >> -#define in_ia32_syscall() true
> >> +#define in_ia32_syscall() (!(current->flags & PF_KTHREAD))
> >> #else
> >> #define in_ia32_syscall() (IS_ENABLED(CONFIG_IA32_EMULATION) && \
> >> current_thread_info()->status & TS_COMPAT)
> >>
> >> This came up in the (no out-of-tree) lustre filesystem where some code
> >> needs to assume 32-bit mode in X86_32 syscalls, and 64-bit mode in kernel
> >> threads.
> >>
> >
> > I could get on board with:
> >
> > ({WARN_ON_ONCE(current->flags & PF_KTHREAD); true})
> >
> > The point of these accessors is to be used *in a syscall*.
> >
> > What on Earth is Lustre doing that makes it have this problem?
>
> Lustre uses it in the ->getattr method to make sure ->ino, ->dev and
> ->rdev are appropriately sized. This isn't very different from the
> usage in ext4 to ensure the seek offset for directories is suitable.
>
> These interfaces can be used both from systemcalls and from kernel
> threads, such as via nfsd.
>
> I don't *know* if nfsd is the particular kthread that causes problems
> for lustre. All I know is that ->getattr returns 32bit squashed inode
> numbers in kthread context where 64 bit numbers would be expected.
>
Well, that looks like Lustre is copying an ext4 bug.
Hi ext4 people-
ext4's is_32bit_api() function is bogus. You can't use
in_compat_syscall() unless you know you're in a syscall
The buggy code was introduced in:
commit d1f5273e9adb40724a85272f248f210dc4ce919a
Author: Fan Yong <yong.fan@whamcloud.com>
Date: Sun Mar 18 22:44:40 2012 -0400
ext4: return 32/64-bit dir name hash according to usage type
I don't know what the right solution is. Al, is it legit at all for
fops->llseek to care about the caller's bitness? If what ext4 is
doing is legit, then ISTM the VFS needs to gain a new API to tell
->llseek what to do. But I'm wondering why FMODE_64BITHASH by itself
isn't sufficient,
I'm quite tempted to add a warning to the x86 arch code to try to
catch this type of bug. Fortunately, a bit of grepping suggests that
ext4 is the only filesystem with this problem.
--Andy
next prev parent reply other threads:[~2018-10-18 17:26 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-11 15:22 [PATCH] x86/vdso: add mremap hook to vm_special_mapping Dmitry Safonov
2016-04-11 15:41 ` kbuild test robot
2016-04-11 15:54 ` Dmitry Safonov
2016-04-14 16:32 ` [PATCHv2] " Dmitry Safonov
2016-04-14 22:58 ` Andy Lutomirski
2016-04-15 8:46 ` Dmitry Safonov
2016-04-15 9:18 ` Ingo Molnar
2016-04-15 9:51 ` Dmitry Safonov
2016-04-15 12:08 ` Dmitry Safonov
2016-04-15 13:20 ` [PATCHv3 1/2] " Dmitry Safonov
2016-04-15 13:20 ` [PATCHv3 2/2] x86: rename is_{ia32,x32}_task to in_{ia32,x32}_syscall Dmitry Safonov
2016-04-15 16:52 ` Andy Lutomirski
2016-04-15 16:55 ` Dmitry Safonov
2016-04-15 13:53 ` [PATCHv3 1/2] x86/vdso: add mremap hook to vm_special_mapping kbuild test robot
2016-04-15 14:12 ` [PATCHv4 " Dmitry Safonov
2016-04-15 14:12 ` [PATCHv4 2/2] x86: rename is_{ia32,x32}_task to in_{ia32,x32}_syscall Dmitry Safonov
2016-04-15 16:58 ` [PATCHv4 1/2] x86/vdso: add mremap hook to vm_special_mapping Andy Lutomirski
2016-04-18 11:18 ` Dmitry Safonov
2016-04-18 15:37 ` Andy Lutomirski
2016-04-18 13:43 ` [PATCHv5 1/3] x86: rename is_{ia32,x32}_task to in_{ia32,x32}_syscall Dmitry Safonov
2016-04-18 13:43 ` [PATCHv5 2/3] x86/vdso: add mremap hook to vm_special_mapping Dmitry Safonov
2016-04-18 14:03 ` kbuild test robot
2016-04-18 14:17 ` [PATCHv6 " Dmitry Safonov
2016-04-18 14:23 ` [PATCHv7 " Dmitry Safonov
2016-04-20 16:22 ` Dmitry Safonov
2016-04-21 19:52 ` Andy Lutomirski
2016-04-22 10:45 ` Dmitry Safonov
2016-04-23 23:09 ` [PATCHv5 " kbuild test robot
2016-04-18 13:43 ` [PATCHv5 3/3] selftest/x86: add mremap vdso 32-bit test Dmitry Safonov
2016-04-21 20:01 ` Andy Lutomirski
2016-04-22 11:34 ` Dmitry Safonov
2016-04-19 9:34 ` [tip:x86/asm] x86/entry: Rename is_{ia32,x32}_task() to in_{ia32,x32}_syscall() tip-bot for Dmitry Safonov
2016-04-19 11:15 ` Ingo Molnar
2016-04-19 11:35 ` Borislav Petkov
2016-04-19 17:00 ` H. Peter Anvin
2016-04-19 16:04 ` Andy Lutomirski
2016-04-22 8:36 ` Ingo Molnar
2018-10-18 1:47 ` in_compat_syscall() returns from kernel thread for X86_32 NeilBrown
2018-10-18 2:37 ` Andy Lutomirski
2018-10-18 2:49 ` Al Viro
2018-10-18 4:36 ` NeilBrown
2018-10-18 17:26 ` Andy Lutomirski [this message]
2018-10-20 6:02 ` Andreas Dilger
2018-10-20 7:58 ` Andy Lutomirski
2018-10-24 1:47 ` NeilBrown
2018-10-24 13:15 ` Theodore Y. Ts'o
2018-10-24 14:32 ` Theodore Y. Ts'o
2019-01-11 22:21 ` Pavel Machek
2018-10-25 3:46 ` NeilBrown
2018-10-25 4:45 ` Andy Lutomirski
2016-04-25 11:37 ` [PATCHv8 1/2] x86/vdso: add mremap hook to vm_special_mapping Dmitry Safonov
2016-04-25 11:37 ` [PATCHv8 2/2] selftest/x86: add mremap vdso test Dmitry Safonov
2016-04-25 21:39 ` Andy Lutomirski
2016-04-25 21:38 ` [PATCHv8 1/2] x86/vdso: add mremap hook to vm_special_mapping Andy Lutomirski
[not found] ` <e0a10957-ddf7-1bc4-fad6-8b5836628fce@virtuozzo.com>
2016-05-05 11:52 ` Ingo Molnar
2016-05-05 11:55 ` Dmitry Safonov
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='CALCETrWH342Y7jKHsYdT=_3fuyDkWhvQLK9z4PTs9jzbfoCVwg@mail.gmail.com' \
--to=luto@kernel.org \
--cc=adilger.kernel@dilger.ca \
--cc=bp@alien8.de \
--cc=brgerst@gmail.com \
--cc=dsafonov@virtuozzo.com \
--cc=dvlasenk@redhat.com \
--cc=hpa@zytor.com \
--cc=jsimmons@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=neilb@suse.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=tytso@mit.edu \
/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).