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![Mark Rutland](/assets/img/avatar_default.png)
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 <linux/kasan-tags.h>. There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Konovalov <andreyknvl@gmail.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Peter Collingbourne <pcc@google.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Will Deacon <will@kernel.org> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com> Tested-by: Andrey Konovalov <andreyknvl@gmail.com> Link: https://lore.kernel.org/r/20210714143843.56537-3-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
15 lines
487 B
C
15 lines
487 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_KASAN_TAGS_H
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#define _LINUX_KASAN_TAGS_H
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#define KASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
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#define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
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#define KASAN_TAG_MAX 0xFD /* maximum value for random tags */
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#ifdef CONFIG_KASAN_HW_TAGS
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#define KASAN_TAG_MIN 0xF0 /* minimum value for random tags */
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#else
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#define KASAN_TAG_MIN 0x00 /* minimum value for random tags */
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#endif
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#endif /* LINUX_KASAN_TAGS_H */
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