linux-kernel - Re: [PATCH] arm64: fix address fault during mapping fdt region

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Date:	Mon, 1 Aug 2016 14:31:20 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	zijun_hu <zijun_hu@...o.com>
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Laura Abbott <labbott@...oraproject.org>,
	"Suzuki K. Poulose" <suzuki.poulose@....com>,
	Jeremy Linton <jeremy.linton@....com>, tj@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, zijun_hu@....com
Subject: Re: [PATCH] arm64: fix address fault during mapping fdt region

On Mon, Aug 01, 2016 at 09:17:09PM +0800, zijun_hu wrote:
> On 08/01/2016 07:24 PM, Mark Rutland wrote:
> > On Mon, Aug 01, 2016 at 06:59:50PM +0800, zijun_hu wrote:
> >> 2，it is more portable; we only need to call fdt_check_header() and don't
> >> care about fdt header filed layout; moreover,fdt module is another independent
> >> module and arm64 only uses it and should not depend on more details of fdt
> >> such as size and magic fields locate within the first MIN_FDT_ALIGN bytes;
> >> the decision whether a fdt header is corrupted should be left to fdt team
> > 
> > While it's true that we assume knowledge of the FDT format, and ideally
> > we'd leave this to common code, we do so regardless by requiring the
> > header size. So both approaches assume details regarding the FDT format.
> > 
> okay, the only thing my solution is depends on is the fdt header struct name
> which maybe remain unchanged in further fdt source modification
> regardless of fields layout or position or header size;
> 
> by the way, my solution only maps more one SWAPPER_BLOCK_SIZE at extreme condition
> (offset + sizeof(struct fdt_header)) > SWAPPER_BLOCK_SIZE, it can occurs very rarely,
> even it happens, it is no matter due to the fast mapping operations
> 
> That all said, ard.biesheuvel's can resolves address fault too, you can decide which
> solution to used, maybe ask fdt team for some advisements

As a member of the "fdt team" (at least for bindings and the spec), I'm
happy with Ard's patch. ;)

Regardless, many thanks for the report, and the proposed fix!

Thanks,
Mark.