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20:35:49 +0100, Catalin Marinas wrote: >On Mon, Aug 25, 2025 at 10:24:26PM +0200, Maciej Wieczor-Retman wrote: >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index e9bbfacc35a6..82cbfc7d1233 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -431,11 +431,11 @@ config KASAN_SHADOW_OFFSET >> default 0xdffffe0000000000 if ARM64_VA_BITS_42 && !KASAN_SW_TAGS >> default 0xdfffffc000000000 if ARM64_VA_BITS_39 && !KASAN_SW_TAGS >> default 0xdffffff800000000 if ARM64_VA_BITS_36 && !KASAN_SW_TAGS >> - default 0xefff800000000000 if (ARM64_VA_BITS_48 || (ARM64_VA_BITS_52 && !ARM64_16K_PAGES)) && KASAN_SW_TAGS >> - default 0xefffc00000000000 if (ARM64_VA_BITS_47 || ARM64_VA_BITS_52) && ARM64_16K_PAGES && KASAN_SW_TAGS >> - default 0xeffffe0000000000 if ARM64_VA_BITS_42 && KASAN_SW_TAGS >> - default 0xefffffc000000000 if ARM64_VA_BITS_39 && KASAN_SW_TAGS >> - default 0xeffffff800000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS >> + default 0xffff800000000000 if (ARM64_VA_BITS_48 || (ARM64_VA_BITS_52 && !ARM64_16K_PAGES)) && KASAN_SW_TAGS >> + default 0xffffc00000000000 if (ARM64_VA_BITS_47 || ARM64_VA_BITS_52) && ARM64_16K_PAGES && KASAN_SW_TAGS >> + default 0xfffffe0000000000 if ARM64_VA_BITS_42 && KASAN_SW_TAGS >> + default 0xffffffc000000000 if ARM64_VA_BITS_39 && KASAN_SW_TAGS >> + default 0xfffffff800000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS >> default 0xffffffffffffffff >> >> config UNWIND_TABLES >> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h >> index 5213248e081b..277d56ceeb01 100644 >> --- a/arch/arm64/include/asm/memory.h >> +++ b/arch/arm64/include/asm/memory.h >> @@ -89,7 +89,15 @@ >> * >> * KASAN_SHADOW_END is defined first as the shadow address that corresponds to >> * the upper bound of possible virtual kernel memory addresses UL(1) << 64 >> - * according to the mapping formula. >> + * according to the mapping formula. For Generic KASAN, the address in the >> + * mapping formula is treated as unsigned (part of the compiler's ABI), so the >> + * end of the shadow memory region is at a large positive offset from >> + * KASAN_SHADOW_OFFSET. For Software Tag-Based KASAN, the address in the >> + * formula is treated as signed. Since all kernel addresses are negative, they >> + * map to shadow memory below KASAN_SHADOW_OFFSET, making KASAN_SHADOW_OFFSET >> + * itself the end of the shadow memory region. (User pointers are positive and >> + * would map to shadow memory above KASAN_SHADOW_OFFSET, but shadow memory is >> + * not allocated for them.) >> * >> * KASAN_SHADOW_START is defined second based on KASAN_SHADOW_END. The shadow >> * memory start must map to the lowest possible kernel virtual memory address >> @@ -100,7 +108,11 @@ >> */ >> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) >> #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL) >> +#ifdef CONFIG_KASAN_GENERIC >> #define KASAN_SHADOW_END ((UL(1) << (64 - KASAN_SHADOW_SCALE_SHIFT)) + KASAN_SHADOW_OFFSET) >> +#else >> +#define KASAN_SHADOW_END KASAN_SHADOW_OFFSET >> +#endif >> #define _KASAN_SHADOW_START(va) (KASAN_SHADOW_END - (UL(1) << ((va) - KASAN_SHADOW_SCALE_SHIFT))) >> #define KASAN_SHADOW_START _KASAN_SHADOW_START(vabits_actual) >> #define PAGE_END KASAN_SHADOW_START >> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c >> index d541ce45daeb..dc2de12c4f26 100644 >> --- a/arch/arm64/mm/kasan_init.c >> +++ b/arch/arm64/mm/kasan_init.c >> @@ -198,8 +198,11 @@ static bool __init root_level_aligned(u64 addr) >> /* The early shadow maps everything to a single page of zeroes */ >> asmlinkage void __init kasan_early_init(void) >> { >> - BUILD_BUG_ON(KASAN_SHADOW_OFFSET != >> - KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT))); >> + if (IS_ENABLED(CONFIG_KASAN_GENERIC)) >> + BUILD_BUG_ON(KASAN_SHADOW_OFFSET != >> + KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT))); >> + else >> + BUILD_BUG_ON(KASAN_SHADOW_OFFSET != KASAN_SHADOW_END); >> BUILD_BUG_ON(!IS_ALIGNED(_KASAN_SHADOW_START(VA_BITS), SHADOW_ALIGN)); >> BUILD_BUG_ON(!IS_ALIGNED(_KASAN_SHADOW_START(VA_BITS_MIN), SHADOW_ALIGN)); >> BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, SHADOW_ALIGN)); > >For the arm64 parts: > >Acked-by: Catalin Marinas Thanks :) > >I wonder whether it's worth keeping the generic KASAN mode for arm64. >We've had the hardware TBI from the start, so the architecture version >is not an issue. The compiler support may differ though. > >Anyway, that would be more suitable for a separate cleanup patch. > >-- >Catalin I want to test it at some point, but I was always under the impression (that at least in theory) different modes should be able to catch slightly different errors. Not a big set but an example being accessing wrong address, but allocated memory - on Generic it should be okay since shadow memory only says if and how much is allocated. On sw-tags it will fault because randomized tags would mismatch. Now I can't think of any examples the other way around but I assume there is a few. -- Kind regards Maciej Wieczór-Retman