Messages in this thread | | | Date | Fri, 29 Apr 2022 16:07:52 +0100 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH 2/2] ARM: Clamp MAX_DMA_ADDRESS to 32-bit |
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On Thu, Mar 24, 2022 at 09:31:56PM +0100, Geert Uytterhoeven wrote: > Hi Florian, > > On Thu, Mar 24, 2022 at 6:54 PM Florian Fainelli <f.fainelli@gmail.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@gmail.com> > > > --- 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) ? \ > > "arm_dma_zone_size < (0x10000000 - PAGE_OFFSET)" looks > like an overflow-avoiding version of > "PAGE_OFFSET + arm_dma_zone_size < 0x10000000". > However, PAGE_OFFSET is always larger than 0x10000000, > so "0x10000000 - PAGE_OFFSET" is a rather large number?
This, to me, looks like it should have been:
arm_dma_zone_size && arm_dma_zone_size < (0x100000000 - PAGE_OFFSET) ? \
since that is the only thing that would make sense - it's the virtual space remaining between PAGE_OFFSET and the top of addressable space.
However, 0x100000000 isn't correct - since the vectors live at 0xffff0000, and we have the vmalloc space etc.
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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