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 ytXwE6P7 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025-02-11 at 09:58:22 +0100, Maciej Wieczor-Retman wrote: >On 2025-02-10 at 23:57:10 +0100, Andrey Konovalov wrote: >>On Mon, Feb 10, 2025 at 4:53 PM Maciej Wieczor-Retman >> wrote: >>> >>> On 2025-02-10 at 16:22:41 +0100, Maciej Wieczor-Retman wrote: >>> >On 2024-10-23 at 20:41:57 +0200, Andrey Konovalov wrote: >>> >>On Tue, Oct 22, 2024 at 3:59 AM Samuel Holland >>> >> wrote: >>> >... >>> >>> + * Software Tag-Based KASAN, the displacement is signed, so >>> >>> + * KASAN_SHADOW_OFFSET is the center of the range. >>> >>> */ >>> >>> - if (addr < KASAN_SHADOW_OFFSET) >>> >>> - return; >>> >>> + if (IS_ENABLED(CONFIG_KASAN_GENERIC)) { >>> >>> + if (addr < KASAN_SHADOW_OFFSET || >>> >>> + addr >= KASAN_SHADOW_OFFSET + max_shadow_size) >>> >>> + return; >>> >>> + } else { >>> >>> + if (addr < KASAN_SHADOW_OFFSET - max_shadow_size / 2 || >>> >>> + addr >= KASAN_SHADOW_OFFSET + max_shadow_size / 2) >>> >>> + return; >>> >> >>> >>Hm, I might be wrong, but I think this check does not work. >>> >> >>> >>Let's say we have non-canonical address 0x4242424242424242 and number >>> >>of VA bits is 48. >>> >> >>> >>Then: >>> >> >>> >>KASAN_SHADOW_OFFSET == 0xffff800000000000 >>> >>kasan_mem_to_shadow(0x4242424242424242) == 0x0423a42424242424 >>> >>max_shadow_size == 0x1000000000000000 >>> >>KASAN_SHADOW_OFFSET - max_shadow_size / 2 == 0xf7ff800000000000 >>> >>KASAN_SHADOW_OFFSET + max_shadow_size / 2 == 0x07ff800000000000 (overflows) >>> >> >>> >>0x0423a42424242424 is < than 0xf7ff800000000000, so the function will >>> >>wrongly return. >>> > >>> >As I understand this check aims to figure out if the address landed in shadow >>> >space and if it didn't we can return. >>> > >>> >Can't this above snippet be a simple: >>> > >>> > if (!addr_in_shadow(addr)) >>> > return; >>> > >>> >? >>> >>> Sorry, I think this wouldn't work. The tag also needs to be reset. Does this >>> perhaps work for this problem? >>> >>> if (!addr_in_shadow(kasan_reset_tag((void *)addr))) >>> return; >> >>This wouldn't work as well. >> >>addr_in_shadow() checks whether an address belongs to the proper >>shadow memory area. That area is the result of the memory-to-shadow >>mapping applied to the range of proper kernel addresses. >> >>However, what we want to check in this function is whether the given >>address can be the result of the memory-to-shadow mapping for some >>memory address, including userspace addresses, non-canonical >>addresses, etc. So essentially we need to check whether the given >>address belongs to the area that is the result of the memory-to-shadow >>mapping applied to the whole address space, not only to proper kernel >>addresses.k > >Ah, okay, I get it. Would the old version > > if (addr < KASAN_SHADOW_OFFSET) > return; > >work if the *addr* had kasan_reset_tag() around it? That would sort of re-unsign >the address only for the purpose of the if(). > >Also I was thinking about it because x86 even with address masking enabled keeps >bit 63 set, so all kernel addresses will be negative in the signed >kasan_mem_to_shadow(). That's great for simplifying the KASAN_SHADOW_OFFSET but >it differs from the TBI and risc-v ideas where half of addresses are negative, >hald positive. So the temporary re-unsigning could maybe make it simpler for x86 >and avoid adding separate cases or alternative kasan_non_canonical_hook() >implementation. Oh, nevermind, I see that this is more complicated than that. Sorry for the spam, I'll do some better calculations what is mapped where when doing kasan_mem_to_shadow() and maybe then I'll figure this out. -- Kind regards Maciej Wieczór-Retman