linux-kernel - Re: [PATCH 2/2] ARM: Clamp MAX_DMA

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Date:   Thu, 24 Mar 2022 20:02:59 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Catalin Marinas <catalin.marinas@....com>,
        open list <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rob Herring <robh+dt@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH 2/2] ARM: Clamp MAX_DMA_ADDRESS to 32-bit

On Thu, Mar 24, 2022 at 6:54 PM Florian Fainelli <f.fainelli@...il.com> wrote:

> MAX_DMA_ADDRESS is a virtual address, therefore it needs to fit within a
> 32-bit unsigned quantity. Platforms defining a DMA zone size in
> their machine descriptor can easily overflow this quantity depending on
> the DMA zone size and/or the PAGE_OFFSET setting.
>
> In most cases this is harmless, however in the case of a
> CONFIG_DEBUG_VIRTUAL enabled, __virt_addr_valid() will be unable to
> return that MAX_DMA_ADDRESS is valid because the value passed to that
> function is an unsigned long which has already overflowed.
>
> Fixes: e377cd8221eb ("ARM: 8640/1: Add support for CONFIG_DEBUG_VIRTUAL")
> Fixes: 2fb3ec5c9503 ("ARM: Replace platform definition of ISA_DMA_THRESHOLD/MAX_DMA_ADDRESS")
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij