From 07b742a4d91260bdb61cd4cbe5ec3bba2ae7f6f9 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Tue, 7 Dec 2021 18:32:26 +0000 Subject: [PATCH] arm64: mm: log potential KASAN shadow alias When the kernel is built with KASAN_GENERIC or KASAN_SW_TAGS, shadow memory is allocated and mapped for all legitimate kernel addresses, and prior to a regular memory access instrumentation will read from the corresponding shadow address. Due to the way memory addresses are converted to shadow addresses, bogus pointers (e.g. NULL) can generate shadow addresses out of the bounds of allocated shadow memory. For example, with KASAN_GENERIC and 48-bit VAs, NULL would have a shadow address of dfff800000000000, which falls between the TTBR ranges. To make such cases easier to debug, this patch makes die_kernel_fault() dump the real memory address range for any potential KASAN shadow access using kasan_non_canonical_hook(), which results in fault information as below when KASAN is enabled: | Unable to handle kernel paging request at virtual address dfff800000000017 | KASAN: null-ptr-deref in range [0x00000000000000b8-0x00000000000000bf] | Mem abort info: | ESR = 0x96000004 | EC = 0x25: DABT (current EL), IL = 32 bits | SET = 0, FnV = 0 | EA = 0, S1PTW = 0 | FSC = 0x04: level 0 translation fault | Data abort info: | ISV = 0, ISS = 0x00000004 | CM = 0, WnR = 0 | [dfff800000000017] address between user and kernel address ranges Signed-off-by: Mark Rutland Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Will Deacon Tested-by: Andrey Konovalov Acked-by: Will Deacon Link: https://lore.kernel.org/r/20211207183226.834557-3-mark.rutland@arm.com Signed-off-by: Catalin Marinas --- arch/arm64/mm/fault.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index b7b9caa..9a9e767 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -297,6 +297,8 @@ static void die_kernel_fault(const char *msg, unsigned long addr, pr_alert("Unable to handle kernel %s at virtual address %016lx\n", msg, addr); + kasan_non_canonical_hook(addr); + mem_abort_decode(esr); show_pte(addr); -- 2.7.4