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From: Borislav Petkov <bp@alien8.de>
To: Tony Luck <tony.luck@intel.com>
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, 13 Sep 2021 11:24:53 +0200	[thread overview]
Message-ID: <YT8Y5cBiaD3NpAIi@zn.tnic> (raw)
In-Reply-To: <20210818002942.1607544-2-tony.luck@intel.com>

On Tue, Aug 17, 2021 at 05:29:40PM -0700, Tony Luck wrote:
> Recovery action when get_user() triggers a machine check uses the fixup
> path to make get_user() return -EFAULT.  Also queue_task_work() sets up
> so that kill_me_maybe() will be called on return to user mode to send
> a SIGBUS to the current process.
> 
> But there are places in the kernel where the code assumes that this
> EFAULT return was simply because of a page fault. The code takes some
> action to fix that, and then retries the access. This results in a second
> machine check.
> 
> While processing this second machine check queue_task_work() is called
> again. But since this uses the same callback_head structure that was used
> in the first call, the net result is an entry on the current->task_works
> list that points to itself. When task_work_run() is called it loops
> forever in this code:
> 
>         do {
>                 next = work->next;
>                 work->func(work);
>                 work = next;
>                 cond_resched();
>         } while (work);
> 
> Add a counter (current->mce_count) to keep track of repeated machine
> checks before task_work() is called. First machine check saves the address
> information and calls task_work_add(). Subsequent machine checks before
> that task_work call back is executed check that the address is in the
> same page as the first machine check (since the callback will offline
> exactly one page).
> 
> Expected worst case is two machine checks before moving on (e.g. one user
> access with page faults disabled, then a repeat to the same addrsss with
> page faults enabled). Just in case there is some code that loops forever
> enforce a limit of 10.
> 
> Cc: <stable@vger.kernel.org>

What about a Fixes: tag?

I guess backporting this to the respective kernels is predicated upon
the existence of those other "places" in the kernel where code assumes
the EFAULT was because of a #PF.

Hmmm?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  parent reply	other threads:[~2021-09-13  9:25 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
2021-09-13  9:24     ` Borislav Petkov [this message]
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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