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KASAN, kasan_mem_to_shadow() uses the logical right shift >> + * For Generic KASAN and Software Tag-Based mode on the x86 >> + * architecture, kasan_mem_to_shadow() uses the logical right shift >> * and never overflows with the chosen KASAN_SHADOW_OFFSET values (on >> * both x86 and arm64). Thus, the possible shadow addresses (even for >> * bogus pointers) belong to a single contiguous region that is the >> * result of kasan_mem_to_shadow() applied to the whole address space. >> */ >> - if (IS_ENABLED(CONFIG_KASAN_GENERIC)) { >> + if (IS_ENABLED(CONFIG_KASAN_GENERIC) || IS_ENABLED(CONFIG_X86_64)) { > >Not a functionality but just a code organization related concern: > >Here, we embed the CONFIG_X86_64 special case in the core KASAN code, >but the __kasan_mem_to_shadow definition to use the logical shift >exists in the x86-64 arch code, and it just copy-pastes one of the >cases from the core kasan_mem_to_shadow definition. > >Should we just move the x86-64 special case to the core KASAN code too >then? I.e., change the kasan_mem_to_shadow definition in >include/linux/kasan.h to check for IS_ENABLED(CONFIG_X86_64)). > >And we could also add a comment there explaining how using the logical >shift for SW_TAGS benefits some architectures (just arm64 for now, but >riscv in the future as well). And put your comment about why it's not >worth it for x86 there as well. > >I don't have a strong preference, just an idea. > >Any thoughts? I'm a fan of trying to keep as much arch code in the arch directories. How about before putting a call here instead like: if (IS_ENABLED(CONFIG_KASAN_GENERIC)) { if (addr < (unsigned long)kasan_mem_to_shadow((void *)(0ULL)) || addr > (unsigned long)kasan_mem_to_shadow((void *)(~0ULL))) return; } arch_kasan_non_canonical_hook() There would be the generic non-arch part above (and anything shared that might make sense here in the future) and all the arch related code would be hidden in the per-arch helper. So then we could move the part below: if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) && IS_ENABLED(CONFIG_ARM64)) { if (addr < (unsigned long)kasan_mem_to_shadow((void *)(0xFFULL << 56)) || addr > (unsigned long)kasan_mem_to_shadow((void *)(~0ULL))) return; } to /arch/arm64. For x86 we'd need to duplicate the generic part into arch_kasan_non_canonical_hook() call in /arch/x86. That seems quiet tidy to me, granted the duplication isn't great but it would keep the non-arch part as shared as possible. What do you think? > >> if (addr < (unsigned long)kasan_mem_to_shadow((void *)(0ULL)) || >> addr > (unsigned long)kasan_mem_to_shadow((void *)(~0ULL))) >> return; > >There's also a comment lower in the function that needs to be updated >to mention Software Tag-Based mode on arm64 specifically. Okay, I'll add that in > > > > >> -- >> 2.52.0 >> >> -- Kind regards Maciej Wieczór-Retman