linux-kernel - Re: [RFC PATCH v2 1/2] ARM/mm/fault: always goto bad_area when handling with page faults of kernel address

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Message-ID: <20251128022756.9973-1-xieyuanbin1@huawei.com>
Date: Fri, 28 Nov 2025 10:27:56 +0800
From: Xie Yuanbin <xieyuanbin1@...wei.com>
To: <bigeasy@...utronix.de>
CC: <akpm@...ux-foundation.org>, <arnd@...db.de>, <brauner@...nel.org>,
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	<will@...nel.org>, <wozizhi@...weicloud.com>, <xieyuanbin1@...wei.com>
Subject: Re: [RFC PATCH v2 1/2] ARM/mm/fault: always goto bad_area when handling with page faults of kernel address

On Thu, 27 Nov 2025 15:51:27 +0100, Sebastian Andrzej Siewior wrote:
> What is with the patch I sent wrong?

Hi, Sebastian Andrzej Siewior!

There is nothing wrong with your patches, but when you submitted
your patches, this bug has not been reportted:
Link: https://lore.kernel.org/20251126090505.3057219-1-wozizhi@huaweicloud.com

Your patches fixed the missing mitigation, but the aforementioned bug
still exists. I think there might be a better solution that can fix both
bugs at the same time.

We had some discussions about this bug:
Link: https://lore.kernel.org/CAHk-=wh1Wfwt9OFB4AfBbjyeu4JVZuSWQ4A8OoT3W6x9btddfw@mail.gmail.com
Link: https://lore.kernel.org/20251126192640.GD3538@ZenIV
Link: https://lore.kernel.org/aSeNtFxD1WRjFaiR@shell.armlinux.org.uk

According to the discussion, it might be better to handle the kernel
address fault directly, just like what x86 does, instead of finding VMA.
Link: https://elixir.bootlin.com/linux/v6.18-rc7/source/arch/x86/mm/fault.c#L1473
```c
	if (unlikely(fault_in_kernel_space(address)))
		do_kern_addr_fault(regs, error_code, address);
	else
		do_user_addr_fault(regs, error_code, address);
```

It seems your patches hasn't been merged into the linux-next branch yet.
This patch is based on linux-next, so it doesn't include your
modifications. This patch might conflict with your patch:
Link: https://lore.kernel.org/20251110145555.2555055-2-bigeasy@linutronix.de
so I'd like to discuss it with you.

Thanks!

Xie Yuanbin