Messages in this thread | | | From | Arnd Bergmann <> | Date | Fri, 29 Apr 2022 17:45:59 +0200 | Subject | Re: [PATCH 1/2] ARM: Fix off by one in checking DMA zone size |
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On Fri, Apr 29, 2022 at 5:15 PM Russell King (Oracle) <linux@armlinux.org.uk> wrote: > > On Thu, Mar 24, 2022 at 10:54:16AM -0700, Florian Fainelli wrote: > > The maximum DMA address is PAGE_OFFSET + arm_dma_zone_size - 1, fix this > > by doing the appropriate subtraction. > > The question is... is MAX_DMA_ADDRESS inclusive or exclusive. The answer > is rather indeterminant, unfortunately. > > drivers/net/wan/cosa.c: if (b + len >= MAX_DMA_ADDRESS) > > So, if the buffer address + buffer length is equal to MAX_DMA_ADDRESS, > then the buffer is not DMA-able. To me this looks completely wrong. > It's also completely wrong because 'b' is a "unsigned long" which > means on 32-bit, this can wrap.
This driver is on its way out and will be removed in 5.19.
> there's a bunch of memblock allocation functions that use > __pa(MAX_DMA_ADDRESS) as the "min_addr" and if this is a minimum > address, then surely this means that it is also an exclusive value. > > So, I came to the conclusion that MAX_DMA_ADDRESS is supposed to be > exclusive. In other words, where PAGE_OFFSET + sizeof(ram) if > sizeof(ram) is the size in bytes of the RAM, limited to the maximum > addressable virtual address that RAM can be mapped to. > > I don't see an inclusive value being correct, at least not for the cases > I've looekd at.
Looking at the other definitions, I see it's usually either ULONG_MAX (which is inclusive) or an exclusive limit, same as the existing version on arm:
arch/alpha/include/asm/io.h:#define IDENT_ADDR 0xffff800000000000UL arch/alpha/include/asm/dma.h:#define MAX_DMA_ADDRESS (alpha_mv.mv_pci_tbi ? \ arch/alpha/include/asm/dma.h- ~0UL : IDENT_ADDR + 0x01000000) arch/arc/include/asm/dma.h:#define MAX_DMA_ADDRESS 0xC0000000 arch/hexagon/include/asm/dma.h:#define MAX_DMA_ADDRESS (PAGE_OFFSET) arch/ia64/mm/init.c:unsigned long MAX_DMA_ADDRESS = PAGE_OFFSET + 0x100000000UL; arch/m68k/include/asm/dma.h:#define MAX_DMA_ADDRESS PAGE_OFFSET arch/mips/include/asm/dma.h:#define MAX_DMA_ADDRESS PAGE_OFFSET arch/mips/include/asm/dma.h:#define MAX_DMA_ADDRESS (PAGE_OFFSET + 0x01000000) arch/parisc/include/asm/dma.h:#define MAX_DMA_ADDRESS (~0UL) arch/powerpc/include/asm/dma.h:#define MAX_DMA_ADDRESS (~0UL) arch/s390/include/asm/dma.h:#define MAX_DMA_ADDRESS 0x80000000 arch/sparc/include/asm/dma.h:#define MAX_DMA_ADDRESS (~0UL) arch/um/include/asm/dma.h:#define MAX_DMA_ADDRESS (uml_physmem) arch/x86/include/asm/dma.h:#define MAX_DMA_ADDRESS (PAGE_OFFSET + 0x1000000) arch/x86/include/asm/dma.h:#define MAX_DMA_PFN ((16UL * 1024 * 1024) >> PAGE_SHIFT) arch/x86/include/asm/dma.h:#define MAX_DMA_ADDRESS ((unsigned long)__va(MAX_DMA_PFN << PAGE_SHIFT))
The exceptions are: arch/xtensa/include/asm/kmem_layout.h:#define XCHAL_KIO_SIZE 0x10000000 arch/xtensa/include/asm/dma.h:#define MAX_DMA_ADDRESS (PAGE_OFFSET + XCHAL_KIO_SIZE - 1) arch/microblaze/include/asm/dma.h:#define MAX_DMA_ADDRESS (CONFIG_KERNEL_START + memory_size - 1)
Arnd
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