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

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Date:   Thu, 24 Mar 2022 10:54:17 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org (open list),
        linus.walleij@...aro.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rob Herring <robh+dt@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH 2/2] ARM: Clamp MAX_DMA_ADDRESS to 32-bit

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>
---
 arch/arm/include/asm/dma.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/dma.h b/arch/arm/include/asm/dma.h
index f244ee68e814..ea47420babd4 100644
--- a/arch/arm/include/asm/dma.h
+++ b/arch/arm/include/asm/dma.h
@@ -8,10 +8,12 @@
 #ifndef CONFIG_ZONE_DMA
 #define MAX_DMA_ADDRESS	0xffffffffUL
 #else
+#include <linux/minmax.h>
 #define MAX_DMA_ADDRESS	({ \
 	extern phys_addr_t arm_dma_zone_size; \
 	arm_dma_zone_size && arm_dma_zone_size < (0x10000000 - PAGE_OFFSET) ? \
-		(PAGE_OFFSET + arm_dma_zone_size - 1) : 0xffffffffUL; })
+		min_t(phys_addr_t, (PAGE_OFFSET + arm_dma_zone_size - 1), 0xffffffffUL) : \
+		0xffffffffUL; })
 #endif
 
 #ifdef CONFIG_ISA_DMA_API
-- 
2.25.1