dma-debug: Fix the overlap() function to be correct and readable (f39d1b97) · Commits · 戴 / test

Linus noticed how unclean and buggy the overlap() function is: - It uses convoluted (and bug-causing) positive checks for range overlap - instead of using a more natural negative check. - Even the positive checks are buggy: a positive intersection check has four natural cases while we checked only for three, missing the (addr < start && addr2 == end) case for example. - The variables are mis-named, making it non-obvious how the check was done. - It needlessly uses u64 instead of unsigned long. Since these are kernel memory pointers and we explicitly exclude highmem ranges anyway we cannot ever overflow 32 bits, even if we could. (and on 64-bit it doesnt matter anyway) All in one, this function needs a total revamp. I used Linus's suggestions minus the paranoid checks (we cannot overflow really because if we get totally bad DMA ranges passed far more things break in the systems than just DMA debugging). I also fixed a few other small details i noticed. Reported-by:

Linus Torvalds <torvalds@linux-foundation.org> Cc: Joerg Roedel <joerg.roedel@amd.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

lib/dma-debug.c

+12 −12

Original line number	Diff line number	Diff line
		@@ -856,22 +856,21 @@ static void check_for_stack(struct device dev, void addr)
		"stack [addr=%p]\n", addr);
		}

		static inline bool overlap(void addr, u64 size, void start, void *end)
		static inline bool overlap(void addr, unsigned long len, void start, void *end)
		{
		void addr2 = (char )addr + size;
		unsigned long a1 = (unsigned long)addr;
		unsigned long b1 = a1 + len;
		unsigned long a2 = (unsigned long)start;
		unsigned long b2 = (unsigned long)end;

		return ((addr >= start && addr < end) \|\|
		(addr2 >= start && addr2 < end) \|\|
		((addr < start) && (addr2 > end)));
		return !(b1 <= a2 \|\| a1 >= b2);
		}

		static void check_for_illegal_area(struct device dev, void addr, u64 size)
		static void check_for_illegal_area(struct device dev, void addr, unsigned long len)
		{
		if (overlap(addr, size, _text, _etext) \|\|
		overlap(addr, size, __start_rodata, __end_rodata))
		err_printk(dev, NULL, "DMA-API: device driver maps "
		"memory from kernel text or rodata "
		"[addr=%p] [size=%llu]\n", addr, size);
		if (overlap(addr, len, _text, _etext) \|\|
		overlap(addr, len, __start_rodata, __end_rodata))
		err_printk(dev, NULL, "DMA-API: device driver maps memory from kernel text or rodata [addr=%p] [len=%lu]\n", addr, len);
		}

		static void check_sync(struct device *dev,
		@@ -969,7 +968,8 @@ void debug_dma_map_page(struct device dev, struct page page, size_t offset,
		entry->type = dma_debug_single;

		if (!PageHighMem(page)) {
		void addr = ((char )page_address(page)) + offset;
		void *addr = page_address(page) + offset;

		check_for_stack(dev, addr);
		check_for_illegal_area(dev, addr, size);
		}

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