linux-kernel - Re: [V2 PATCH] sparc64/gup: check address scope legitimacy

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Date:	Sat, 5 Dec 2015 10:59:56 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	"Shi, Yang" <yang.shi@...aro.org>
Cc:	davem@...emloft.net, linux-kernel@...r.kernel.org,
	sparclinux@...r.kernel.org, linaro-kernel@...ts.linaro.org
Subject: Re: [V2 PATCH] sparc64/gup: check address scope legitimacy

> >access_ok() always returns 1.
> 
> Thanks for pointing it out. And, I didn't notice that gup is just built for
> SPARC64. I though it is built by both 64 bit and 32 bit.
> 
> A follow-up question, is there any reason to just have sparc specific fast
> gup for 64 bit not for 32 bit?
I do not know - sorry.

> >>@@ -203,6 +206,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> >>  	addr = start;
> >>  	len = (unsigned long) nr_pages << PAGE_SHIFT;
> >>  	end = start + len;
> >>+	if (end < start)
> >>+		goto slow_irqon;
> >
> >end can only be smaller than start if there is some overflow.
> >See how end is calculated just the line above.
> >
> >This looks like a highly suspicious change.
> 
> I'm supposed this is used to protect the overflow. I copied the code from
> other arch. Actually, every arch has this except sparc.
The the other archs are likely confused as well - there is most
likely some history behind that can be found if digging a little.

The code is not present in the generic version.

	Sam
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