linux-kernel - Re: Re: [PATCH RESEND] arm64: add alignment fault hanling

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Date:	Mon, 15 Feb 2016 11:44:54 +0000 (GMT)
From:	EunTaik Lee <eun.taik.lee@...sung.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"will.deacon@....com" <will.deacon@....com>,
	"vladimir.murzin@....com" <vladimir.murzin@....com>,
	"suzuki.poulose@....com" <suzuki.poulose@....com>,
	"riandrews@...roid.com" <riandrews@...roid.com>,
	"james.morse@....com" <james.morse@....com>,
	"salyzyn@...roid.com" <salyzyn@...roid.com>,
	"Dave.Martin@....com" <Dave.Martin@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH RESEND] arm64: add alignment fault hanling

> How do you end up with Device nGnRnE in user space? I thought we should
> have got some guard page.
I guess it is a device file that is mmaped in the user space and later remapped in the kernel
 using pgprot_noncached(). 
I can't find the code that inserts a guard page in between vma's can you please help me find that code?

> do_strncpy_from_user() relies on unsafe_get_user() not being able to
> read 8 bytes. The problem now is that it doesn't get a page fault but an
> alignment one is isn't handled.
Yes.

> Why addr >= TASK_SIZE? addr here should be the fault address, not pc.
You're right. I should have used user_mode(regs).

> The simplest would be to use do_bad_area() here without any additional
> function.
Yes, I should've probably used do_bad_area(). I just wanted to do the minimal stuff.