linux-kernel - Re: [PATCH] arm64: avoid overflow in VA_START and PAGE

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Date:   Thu, 3 Aug 2017 10:53:12 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     zijun_hu <zijun_hu@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Doug Anderson <dianders@...omium.org>,
        Stephen Hines <srhines@...gle.com>,
        Pirama Arumuga Nainar <pirama@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>,
        Oleksandr Andrushchenko <Oleksandr_Andrushchenko@...m.com>,
        Alexander Popov <alex.popov@...ux.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: avoid overflow in VA_START and PAGE_OFFSET

> Would
>
> #define VA_START (UL(0xffffffffffffffff) - (1 << VA_BITS) + 1)
>
> also work?

I think you'd have to wrap the 1 in a UL(), ex:

#define VA_START (UL(0xffffffffffffffff) - (UL(1) << VA_BITS) + 1)

Otherwise IIUC a integral literal (`1`) is treated as an int, which on
arm64 is LP64 making it 32b, where most configs set VA_BITS
to larger than 32b.  Shifting by more than the width is undefined
behavior. And without it, I get compile errors.

I'll send v2 with your suggestion, thanks.
-- 
Thanks,
~Nick Desaulniers