From 82868247897bea2d69a83dca9a6a557e2c96dac4 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Wed, 14 Jul 2021 15:38:42 +0100 Subject: arm64: kasan: mte: use a constant kernel GCR_EL1 value When KASAN_HW_TAGS is selected, KASAN is enabled at boot time, and the hardware supports MTE, we'll initialize `kernel_gcr_excl` with a value dependent on KASAN_TAG_MAX. While the resulting value is a constant which depends on KASAN_TAG_MAX, we have to perform some runtime work to generate the value, and have to read the value from memory during the exception entry path. It would be better if we could generate this as a constant at compile-time, and use it as such directly. Early in boot within __cpu_setup(), we initialize GCR_EL1 to a safe value, and later override this with the value required by KASAN. If CONFIG_KASAN_HW_TAGS is not selected, or if KASAN is disabeld at boot time, the kernel will not use IRG instructions, and so the initial value of GCR_EL1 is does not matter to the kernel. Thus, we can instead have __cpu_setup() initialize GCR_EL1 to a value consistent with KASAN_TAG_MAX, and avoid the need to re-initialize it during hotplug and resume form suspend. This patch makes arem64 use a compile-time constant KERNEL_GCR_EL1 value, which is compatible with KASAN_HW_TAGS when this is selected. This removes the need to re-initialize GCR_EL1 dynamically, and acts as an optimization to the entry assembly, which no longer needs to load this value from memory. The redundant initialization hooks are removed. In order to do this, KASAN_TAG_MAX needs to be visible outside of the core KASAN code. To do this, I've moved the KASAN_TAG_* values into . There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Peter Collingbourne Cc: Vincenzo Frascino Cc: Will Deacon Reviewed-by: Catalin Marinas Reviewed-by: Andrey Konovalov Tested-by: Andrey Konovalov Link: https://lore.kernel.org/r/20210714143843.56537-3-mark.rutland@arm.com Signed-off-by: Catalin Marinas --- mm/kasan/hw_tags.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'mm/kasan/hw_tags.c') diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c index 4ea8c368b5b8..2c6c6c6ddfa2 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -142,8 +142,6 @@ void kasan_init_hw_tags_cpu(void) if (kasan_arg == KASAN_ARG_OFF) return; - hw_init_tags(KASAN_TAG_MAX); - /* * Enable async mode only when explicitly requested through * the command line. -- cgit v1.2.1