linux-kernel - Re: [PATCH] arm64/mm: fix virtual address boundary check

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Message-ID: <1456364073.16470.8.camel@mtkswgap22>
Date:	Thu, 25 Feb 2016 09:34:33 +0800
From:	Miles Chen <miles.chen@...iatek.com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	Will Deacon <will.deacon@....com>, <wsdupstream@...iatek.com>,
	<linux-mediatek@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64/mm: fix virtual address boundary check

On Wed, 2016-02-24 at 16:19 +0000, Catalin Marinas wrote:
> On Thu, Feb 25, 2016 at 12:01:48AM +0800, miles.chen@...iatek.com wrote:
> > From: Miles Chen <miles.chen@...iatek.com>
> > 
> > The MODULES_VADDR is not the lowest possible
> > kernel virtual address. TASK_SIZE_64 may be larger than
> > MODULES_VADDR, FIXADDR_TOP, and PCI_IO_START.
> > 
> > Fix this by comparing TASK_SIZE_64 (highest user virtual address)
> > with VA_START (lowest kernel virtual address).
> > 
> >  #define VA_BITS		(CONFIG_ARM64_VA_BITS)
> >  #define VA_START		(UL(0xffffffffffffffff) << VA_BITS)
> >  #define PAGE_OFFSET		(UL(0xffffffffffffffff) << (VA_BITS - 1))
> >  #define MODULES_END		(PAGE_OFFSET)
> >  #define MODULES_VADDR		(MODULES_END - SZ_64M)
> >  #define PCI_IO_END		(MODULES_VADDR - SZ_2M)
> >  #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
> >  #define FIXADDR_TOP		(PCI_IO_START - SZ_2M)
> >  #define TASK_SIZE_64		(UL(1) << VA_BITS)
> 
> We should remove these checks altogether. There is a huge gap between
> the user and kernel addresses that they would never overlap (we don't
> have enough levels of page tables to cover 64-bit VA space).
> 
Thanks for your reply. I confirmed that in the ARMv8 documentation. 
I'll send another patch to remove these checks.


Cheers,
Miles