linux-kernel - Re: [RFC PATCH] vfs: Fix might sleep in load_unaligned

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Message-ID: <20251128013935.3539-1-xieyuanbin1@huawei.com>
Date: Fri, 28 Nov 2025 09:39:35 +0800
From: Xie Yuanbin <xieyuanbin1@...wei.com>
To: <viro@...iv.linux.org.uk>, <linux@...linux.org.uk>, <will@...nel.org>,
	<david.laight@...box.com>, <rmk+kernel@...linux.org.uk>
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	<jack@...e.com>, <wozizhi@...weicloud.com>, <linux-fsdevel@...r.kernel.org>,
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	<lilinjie8@...wei.com>, <liaohua4@...wei.com>, <wangkefeng.wang@...wei.com>,
	<pangliyuan1@...wei.com>, Xie Yuanbin <xieyuanbin1@...wei.com>
Subject: Re: [RFC PATCH] vfs: Fix might sleep in load_unaligned_zeropad() with rcu read lock held

On Wed, 26 Nov 2025 19:26:40 +0000, Al Viro wrote:
> For quick and dirty variant (on current tree), how about
> adding
> 	if (unlikely(addr > TASK_SIZE) && !user_mode(regs))
> 		goto no_context;
>
> right after
>
> 	if (!ttbr0_usermode_access_allowed(regs))
> 		goto no_context;
>
> in do_page_fault() there?
>
> NOTE: that might or might not break vdso; I don't think it would, but...

On Wed, 26 Nov 2025 23:31:00 +0000, Russell King wrote:
> Now, for 32-bit ARM, I think I am coming to the conclusion that Al's
> suggestion is probably the easiest solution. However, whether it has
> side effects, I couldn't say - the 32-bit ARM fault code has been
> modified by quite a few people in ways I don't yet understand, so I
> can't be certain at the moment whether it would cause problems.
>
> I think the only thing to do is to try the solution and see what
> breaks. I'm not in a position to be able to do that as, having not
> had reason to touch 32-bit ARM for years, I don't have a hackable
> platform nearby. Maybe Xie Yuanbin can test it?

Hi, Al Viro and Russell King!

I moved the judgment forward to before local_irq_enable() and submitted
a new patch:
Link: https://lore.kernel.org/20251127140109.191657-1-xieyuanbin1@huawei.com

This is because there's another bug I reported before that also requires
a similar judgment, but before the interrupt is enabled.
Link: https://lore.kernel.org/20250925025744.6807-1-xieyuanbin1@huawei.com

I hope this can fix both of these bugs.

It is closer to the x86's implementation and works well in current tests.
Could you please take a look? Thanks you very much!

Xie Yuanbin