From: Thomas Gleixner <tglx@linutronix.de>
To: "Luck, Tony" <tony.luck@intel.com>, Al Viro <viro@zeniv.linux.org.uk>
Cc: cluster-devel <cluster-devel@redhat.com>, Jan Kara <jack@suse.cz>,
Andreas Gruenbacher <agruenba@redhat.com>,
x86@kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Borislav Petkov <bp@alien8.de>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable
Date: Sat, 28 Aug 2021 23:47:03 +0200 [thread overview]
Message-ID: <87r1edgs2w.ffs@tglx> (raw)
In-Reply-To: <20210827232246.GA1668365@agluck-desk2.amr.corp.intel.com>
On Fri, Aug 27 2021 at 16:22, Tony Luck wrote:
> On Fri, Aug 27, 2021 at 09:57:10PM +0000, Al Viro wrote:
>> On Fri, Aug 27, 2021 at 09:48:55PM +0000, Al Viro wrote:
>>
>> > [btrfs]search_ioctl()
>> > Broken with memory poisoning, for either variant of semantics. Same for
>> > arm64 sub-page permission differences, I think.
>>
>>
>> > So we have 3 callers where we want all-or-nothing semantics - two in
>> > arch/x86/kernel/fpu/signal.c and one in btrfs. HWPOISON will be a problem
>> > for all 3, AFAICS...
>> >
>> > IOW, it looks like we have two different things mixed here - one that wants
>> > to try and fault stuff in, with callers caring only about having _something_
>> > faulted in (most of the users) and one that wants to make sure we *can* do
>> > stores or loads on each byte in the affected area.
>> >
>> > Just accessing a byte in each page really won't suffice for the second kind.
>> > Neither will g-u-p use, unless we teach it about HWPOISON and other fun
>> > beasts... Looks like we want that thing to be a separate primitive; for
>> > btrfs I'd probably replace fault_in_pages_writeable() with clear_user()
>> > as a quick fix for now...
>> >
>> > Comments?
>>
>> Wait a sec... Wasn't HWPOISON a per-page thing? arm64 definitely does have
>> smaller-than-page areas with different permissions, so btrfs search_ioctl()
>> has a problem there, but arch/x86/kernel/fpu/signal.c doesn't have to deal
>> with that...
>>
>> Sigh... I really need more coffee...
>
> On Intel poison is tracked at the cache line granularity. Linux
> inflates that to per-page (because it can only take a whole page away).
> For faults triggered in ring3 this is pretty much the same thing because
> mm/memory_failure.c unmaps the page ... so while you see a #MC on first
> access, you get #PF when you retry. The x86 fault handler sees a magic
> signature in the page table and sends a SIGBUS.
>
> But it's all different if the #MC is triggerd from ring0. The machine
> check handler can't unmap the page. It just schedules task_work to do
> the unmap when next returning to the user.
>
> But if your kernel code loops and tries again without a return to user,
> then your get another #MC.
But that's not the case for restore_fpregs_from_user() when it hits #MC.
restore_fpregs_from_user()
...
ret = __restore_fpregs_from_user(buf, xrestore, fx_only)
/* Try to handle #PF, but anything else is fatal. */
if (ret != -EFAULT)
return -EINVAL;
Now let's look at __restore_fpregs_from_user()
__restore_fpregs_from_user()
return $FPUVARIANT_rstor_from_user_sigframe()
which all end up in user_insn(). user_insn() returns 0 or the negated
trap number, which results in -EFAULT for #PF, but for #MC the negated
trap number is -18 i.e. != -EFAULT. IOW, there is no endless loop.
This used to be a problem before commit:
aee8c67a4faa ("x86/fpu: Return proper error codes from user access functions")
and as the changelog says the initial reason for this was #GP going into
the fault path, but I'm pretty sure that I also discussed the #MC angle with
Borislav back then. Should have added some more comments there
obviously.
Thanks,
tglx
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next prev parent reply other threads:[~2021-09-13 14:28 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 16:49 [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 01/19] iov_iter: Fix iov_iter_get_pages{, _alloc} page fault return value Andreas Gruenbacher
2021-09-09 11:09 ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 02/19] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 03/19] gup: Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Andreas Gruenbacher
2021-08-27 19:08 ` Al Viro
2021-09-03 14:56 ` Filipe Manana
2021-09-28 15:02 ` Andreas Gruenbacher
2021-09-28 16:37 ` Matthew Wilcox
2021-09-28 20:41 ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 04/19] iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-27 18:53 ` Al Viro
2021-08-27 18:57 ` Linus Torvalds
2021-08-27 19:16 ` Al Viro
2021-08-27 20:56 ` Kari Argillander
2021-08-28 17:13 ` Linus Torvalds
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-27 18:49 ` Al Viro
2021-08-27 19:05 ` Linus Torvalds
2021-08-27 19:23 ` Al Viro
2021-08-27 19:33 ` Linus Torvalds
2021-08-27 19:37 ` Al Viro
2021-08-27 21:48 ` Al Viro
2021-08-27 21:57 ` Al Viro
2021-08-27 23:22 ` Luck, Tony
2021-08-28 2:20 ` Luck, Tony
2021-08-28 21:47 ` Thomas Gleixner [this message]
2021-08-28 22:04 ` Al Viro
2021-08-28 22:11 ` Al Viro
2021-08-28 22:19 ` Al Viro
2021-08-28 22:51 ` Al Viro
2021-08-29 18:44 ` Thomas Gleixner
2021-08-29 19:46 ` Al Viro
2021-08-29 19:51 ` Thomas Gleixner
2021-08-28 22:20 ` Tony Luck
2021-08-29 1:40 ` Matthew Wilcox
2021-08-30 15:41 ` Luck, Tony
2021-08-28 22:23 ` Thomas Gleixner
2021-08-28 19:28 ` [Ocfs2-devel] [RFC][arm64] possible infinite loop in btrfs search_ioctl() Al Viro
2021-08-31 13:54 ` Catalin Marinas
2021-08-31 15:28 ` Al Viro
2021-08-31 16:01 ` Catalin Marinas
2021-10-11 17:37 ` Catalin Marinas
2021-10-11 19:15 ` Linus Torvalds
2021-10-11 21:08 ` Catalin Marinas
2021-10-11 23:59 ` Linus Torvalds
2021-10-12 17:27 ` Catalin Marinas
2021-10-12 17:58 ` Linus Torvalds
2021-10-18 17:13 ` Catalin Marinas
2021-10-21 0:46 ` Andreas Gruenbacher
2021-10-21 10:05 ` Catalin Marinas
2021-10-21 14:42 ` Andreas Gruenbacher
2021-10-21 17:09 ` Catalin Marinas
2021-10-21 18:00 ` Andreas Gruenbacher
2021-10-22 18:41 ` Catalin Marinas
2021-10-25 19:37 ` Andreas Gruenbacher
2021-10-22 2:30 ` Linus Torvalds
2021-10-22 9:34 ` Catalin Marinas
2021-08-29 0:58 ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Al Viro
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 06/19] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 07/19] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 08/19] gfs2: Eliminate vestigial HIF_FIRST Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 09/19] gfs2: Remove redundant check from gfs2_glock_dq Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 10/19] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 11/19] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 12/19] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 13/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 14/19] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-09-03 18:54 ` Darrick J. Wong
2021-09-09 11:17 ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-09-03 18:54 ` Darrick J. Wong
2021-09-09 11:20 ` Christoph Hellwig
2021-09-28 15:05 ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 16/19] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-27 18:30 ` Darrick J. Wong
2021-08-27 20:15 ` Andreas Gruenbacher
2021-08-27 21:32 ` Darrick J. Wong
2021-08-27 21:49 ` Andreas Grünbacher
2021-08-27 22:35 ` Linus Torvalds
2021-09-03 18:47 ` Darrick J. Wong
2021-09-03 18:53 ` Darrick J. Wong
2021-09-09 11:30 ` Christoph Hellwig
2021-09-09 17:22 ` Linus Torvalds
2021-09-10 7:36 ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 17/19] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-09-09 11:36 ` Christoph Hellwig
2021-09-09 17:17 ` Linus Torvalds
2021-09-10 7:24 ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 18/19] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-08-27 18:47 ` Al Viro
2021-08-27 19:56 ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 19/19] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-27 17:16 ` [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-09-01 19:52 ` Andreas Gruenbacher
2021-09-03 15:52 ` Linus Torvalds
2021-09-03 18:25 ` Al Viro
2021-09-03 18:47 ` Linus Torvalds
2021-09-03 19:51 ` Andreas Grünbacher
2021-09-03 15:07 ` Filipe Manana
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