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 BeY6Zpa+ 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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 2025-02-17 at 17:13:23 +0100, Andrey Konovalov wrote: >On Fri, Feb 14, 2025 at 9:21 AM Maciej Wieczor-Retman > wrote: >> >> On 2025-02-13 at 17:20:22 +0100, Maciej Wieczor-Retman wrote: >> >On 2025-02-13 at 02:28:08 +0100, Andrey Konovalov wrote: >> >>On Thu, Feb 13, 2025 at 2:21 AM Andrey Konovalov wrote: >> >>> >> >>> On Tue, Feb 11, 2025 at 7:07 PM Maciej Wieczor-Retman >> >>> wrote: >> >>> > >> >>> > I did some experiments with multiple addresses passed through >> >>> > kasan_mem_to_shadow(). And it seems like we can get almost any address out when >> >>> > we consider any random bogus pointers. >> >>> > >> >>> > I used the KASAN_SHADOW_OFFSET from your example above. Userspace addresses seem >> >>> > to map to the range [KASAN_SHADOW_OFFSET - 0xffff8fffffffffff]. Then going >> >>> > through non-canonical addresses until 0x0007ffffffffffff we reach the end of >> >>> > kernel LA and we loop around. Then the addresses seem to go from 0 until we >> >>> > again start reaching the kernel space and then it maps into the proper shadow >> >>> > memory. >> >>> > >> >>> > It gave me the same results when using the previous version of >> >>> > kasan_mem_to_shadow() so I'm wondering whether I'm doing this experiment >> >>> > incorrectly or if there aren't any addresses we can rule out here? >> >>> >> >>> By the definition of the shadow mapping, if we apply that mapping to >> >>> the whole 64-bit address space, the result will only contain 1/8th >> >>> (1/16th for SW/HW_TAGS) of that space. >> >>> >> >>> For example, with the current upstream value of KASAN_SHADOW_OFFSET on >> >>> x86 and arm64, the value of the top 3 bits (4 for SW/HW_TAGS) of any >> >>> shadow address are always the same: KASAN_SHADOW_OFFSET's value is >> >>> such that the shadow address calculation never overflows. Addresses >> >>> that have a different value for those top 3 bits are the once we can >> >>> rule out. >> >> >> >>Eh, scratch that, the 3rd bit from the top changes, as >> >>KASAN_SHADOW_OFFSET is not a that-well-aligned value, the overall size >> >>of the mapping holds. >> >> >> >>> The KASAN_SHADOW_OFFSET value from my example does rely on the >> >>> overflow (arguably, this makes things more confusing [1]). But still, >> >>> the possible values of shadow addresses should only cover 1/16th of >> >>> the address space. >> >>> >> >>> So whether the address belongs to that 1/8th (1/16th) of the address >> >>> space is what we want to check in kasan_non_canonical_hook(). >> >>> >> > >> >Right, I somehow forgot that obviously the whole LA has to map to 1/16th of the >> >address space and it shold stay contiguous. >> > >> >After rethinking how the mapping worked before and will work after making stuff >> >signed I thought this patch could make use of the overflow? >> > >> >From what I noticed, all the Kconfig values for KASAN_SHADOW_OFFSET should make >> >it so there will be overflow when inputing more and more positive addresses. >> > >> >So maybe we should first find what the most negative and most positive (signed) >> >addresses map to in shadow memory address space. And then when looking for >> >invalid values that aren't the product of kasan_mem_to_shadow() we should check >> > >> > if (addr > kasan_mem_to_shadow(biggest_positive_address) && >> > addr < kasan_mem_to_shadow(smallest_negative_address)) >> > return; >> > >> >Is this correct? >> >> I suppose the original code in the patch does the same thing when you change the >> || into &&: >> >> if (addr < KASAN_SHADOW_OFFSET - max_shadow_size / 2 && >> addr >= KASAN_SHADOW_OFFSET + max_shadow_size / 2) >> return; >> >> kasan_mem_to_shadow(0x7FFFFFFFFFFFFFFF) -> 0x07ff7fffffffffff >> kasan_mem_to_shadow(0x8000000000000000) -> 0xf7ff800000000000 > >I'm a bit lost with these calculations at this point. Please send the >full patch, including the new values for KASAN_SHADOW_OFFSET (do I >understand correctly that you want to change them?). It'll be easier >to look at the code. Sorry, this thread became a little bit confusing. No, I think the KASAN_SHADOW_OFFSET values are fine. I just wanted to embrace the idea of overflow for the purpose of the check in kasan_non_canonical_hook(). But I'll put down my train of thought about the overflow + calculations in the patch message. > >Feel free to send this patch separately from the rest of the series, >so that we can finalize it first. I have the x86 tag-based series basically ready (just need to re-read it) so I think I can send it as whole with this patch and 3 others from this series. -- Kind regards Maciej Wieczór-Retman