From: "Luck, Tony" <tony.luck@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Jue Wang <juew@google.com>, Ding Hui <dinghui@sangfor.com.cn>,
naoya.horiguchi@nec.com, osalvador@suse.de,
Youquan Song <youquan.song@intel.com>,
huangcun@sangfor.com.cn, x86@kernel.org,
linux-edac@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery
Date: Mon, 23 Aug 2021 08:24:37 -0700 [thread overview]
Message-ID: <20210823152437.GA1637466@agluck-desk2.amr.corp.intel.com> (raw)
In-Reply-To: <YSJjNlTJiBx1v1SS@zn.tnic>
On Sun, Aug 22, 2021 at 04:46:14PM +0200, Borislav Petkov wrote:
> On Fri, Aug 20, 2021 at 01:33:56PM -0700, Luck, Tony wrote:
> > The new version (thanks to All fixing iov_iter.c) now does
> > exactly what POSIX says should happen. If I have a buffer
> > with poison at offset 213, and I do this:
> >
> > ret = write(fd, buf, 512);
> >
> > Then the return from write is 213, and the first 213 bytes
> > from the buffer appear in the file, and the file size is
> > incremented by 213 (assuming the write started with the lseek
> > offset at the original size of the file).
>
> ... and the user still gets a SIGBUS so that it gets a chance to handle
> the encountered poison? I.e., not retry the write for the remaining 512
> - 213 bytes?
Whether the user gets a SIGBUS depends on what they do next. In a typical
user loop trying to do a write:
while (nbytes) {
ret = write(fd, buf, nbytes);
if (ret == -1)
return ret;
buf += ret;
nbytes -= ret;
}
The next iteration after the short write caused by the machine check
will return ret == -1, errno = EFAULT.
Andy Lutomirski convinced me that the kernel should not send a SIGBUS
to an application when the kernel accesses the poison in user memory.
If the user tries to access the page with the poison directly they'll
get a SIGBUS (page was unmapped so user gets a #PF, but the x86 fault
handler sees that the page was unmapped because of poison, so sends a
SIGBUS).
> If so, do we document that somewhere so that application writers can
> know what they should do in such cases?
Applications see a failed write ... they should do whatever they would
normally do for a failed write.
-Tony
next prev parent reply other threads:[~2021-08-23 15:24 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-06 19:06 [PATCH 0/3] More machine check recovery fixes Tony Luck
2021-07-06 19:06 ` [PATCH 1/3] x86/mce: Change to not send SIGBUS error during copy from user Tony Luck
2021-07-06 19:06 ` [PATCH 2/3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-07-06 19:06 ` [PATCH 3/3] x86/mce: Drop copyin special case for #MC Tony Luck
2021-08-18 0:29 ` [PATCH v2 0/3] More machine check recovery fixes Tony Luck
2021-08-18 0:29 ` [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-08-20 17:31 ` Borislav Petkov
2021-08-20 18:59 ` Luck, Tony
2021-08-20 19:27 ` Borislav Petkov
2021-08-20 20:23 ` Luck, Tony
2021-08-21 4:51 ` Tony Luck
2021-08-21 21:51 ` Al Viro
2021-08-22 14:36 ` Borislav Petkov
2021-08-20 20:33 ` Luck, Tony
2021-08-22 14:46 ` Borislav Petkov
2021-08-23 15:24 ` Luck, Tony [this message]
2021-09-13 9:24 ` Borislav Petkov
2021-09-13 21:52 ` [PATCH v3] " Luck, Tony
2021-09-14 8:28 ` Borislav Petkov
2021-08-18 0:29 ` [PATCH v2 2/3] x86/mce: Change to not send SIGBUS error during copy from user Tony Luck
2021-09-21 7:52 ` [tip: ras/core] " tip-bot2 for Tony Luck
2021-08-18 0:29 ` [PATCH v2 3/3] x86/mce: Drop copyin special case for #MC Tony Luck
2021-09-20 9:13 ` Borislav Petkov
2021-09-20 16:18 ` Luck, Tony
2021-09-20 16:37 ` Borislav Petkov
2021-09-20 16:43 ` Luck, Tony
2021-09-21 7:52 ` [tip: ras/core] " tip-bot2 for Tony Luck
2021-08-18 16:14 ` [PATCH v2 0/3] More machine check recovery fixes Luck, Tony
-- strict thread matches above, loose matches on Subject: below --
2021-01-08 22:22 [PATCH 0/2] Fix infinite machine check loop in futex_wait_setup() Tony Luck
2021-01-11 21:44 ` [PATCH v2 0/3] " Tony Luck
2021-01-11 21:44 ` [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-11 22:11 ` Andy Lutomirski
2021-01-11 22:20 ` Luck, Tony
2021-01-12 17:00 ` Andy Lutomirski
2021-01-12 17:16 ` Luck, Tony
2021-01-12 17:21 ` Andy Lutomirski
2021-01-12 18:23 ` Luck, Tony
2021-01-12 18:57 ` Andy Lutomirski
2021-01-12 20:52 ` Luck, Tony
2021-01-12 22:04 ` Andy Lutomirski
2021-01-13 1:50 ` Luck, Tony
2021-01-13 4:15 ` Andy Lutomirski
2021-01-13 10:00 ` Borislav Petkov
2021-01-13 16:06 ` Luck, Tony
2021-01-13 16:19 ` Borislav Petkov
2021-01-13 16:32 ` Luck, Tony
2021-01-13 17:35 ` Borislav Petkov
2021-01-14 20:22 ` Borislav Petkov
2021-01-14 21:05 ` Luck, Tony
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