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 QjnlRvSZ 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wrote: >>> >>> >Is there any reason we need this change for x86 SW_TAGS besides the >>> >optimization benefits? >>> >>> I wanted to have the shadow memory boundries aligned properly, to not waste page >>> table entries, so the memory map is more straight forward. This patch helps with >>> that, I don't think it would have worked without it. >> >>Ok, I see - let's add this info into the commit message then. > >Sure, but if you like the 0xffeffc0000000000 offset I'll just drop this part. > >> >>> >However, I just realized that this check is not entirely precise. When >>> >doing the memory-to-shadow mapping, the memory address always has its >>> >top byte set to 0xff: both the inlined compiler code and the outline >>> >KASAN code do this >>> >>> Do you mean that non-canonical addresses passed to kasan_mem_to_shadow() will >>> map to the same space that the canonical version would map to? >> >>No, but non-canonical address are never passed to >>kasan_mem_to_shadow(): KASAN always resets the tag before calling this >>function. >> >>> What does that? Does the compiler do something more than is in >>> kasan_mem_to_shadow() when instrumenting functions? >> >>Same for the compiler, it always untags the pointer first [1]. >> >>[1] https://github.com/llvm/llvm-project/blob/llvmorg-20-init/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp#L922 >> >>> > Thus, the possible values a shadow address can >>> >take are the result of the memory-to-shadow mapping applied to >>> >[0xff00000000000000, 0xffffffffffffffff], not to the whole address >>> >space. So we can make this check more precise. >>> >>> In case my question above didn't lead to this: what happens to the rest of the >>> values if they get plugged into kasan_mem_to_shadow()? >> >>We will get some invalid addresses. But this should never happen in >>the first place. > >Thanks for letting me know about the tag resets, that should make changing the >check in kasan_non_canonical_hook() easier. Ah, but the [0xff00000000000000, 0xffffffffffffffff] won't be true for x86 right? Here the tag reset function only resets bits 60:57. So I presume [0x3e00000000000000, 0xffffffffffffffff] would be the range? -- Kind regards Maciej Wieczór-Retman