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 <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Will Deacon <[email protected]>
Tested-by: Andrey Konovalov <[email protected]>
Acked-by: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: mrutland-arm

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);