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authorMark Rutland <mark.rutland@arm.com>2021-07-14 15:38:42 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2021-08-02 18:14:21 +0100
commit82868247897bea2d69a83dca9a6a557e2c96dac4 (patch)
tree6154f97e2b4c00b5a8946d6825b9097d79f76847 /arch/arm64/kernel/mte.c
parentd914b80a8f567d052d621197974ae08f729c963d (diff)
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 <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>
Diffstat (limited to 'arch/arm64/kernel/mte.c')
-rw-r--r--arch/arm64/kernel/mte.c31
1 files changed, 0 insertions, 31 deletions
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 20a40e5a14fa..b538ff27a912 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -23,8 +23,6 @@
#include <asm/ptrace.h>
#include <asm/sysreg.h>
-u64 gcr_kernel_excl __ro_after_init;
-
static bool report_fault_once = true;
static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);
@@ -104,26 +102,6 @@ int memcmp_pages(struct page *page1, struct page *page2)
return ret;
}
-void mte_init_tags(u64 max_tag)
-{
- static bool gcr_kernel_excl_initialized;
-
- if (!gcr_kernel_excl_initialized) {
- /*
- * The format of the tags in KASAN is 0xFF and in MTE is 0xF.
- * This conversion extracts an MTE tag from a KASAN tag.
- */
- u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
- max_tag), 0);
-
- gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
- gcr_kernel_excl_initialized = true;
- }
-
- /* Enable the kernel exclude mask for random tags generation. */
- write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
-}
-
static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
{
/* Enable MTE Sync Mode for EL1. */
@@ -262,15 +240,6 @@ void mte_suspend_enter(void)
mte_check_tfsr_el1();
}
-void mte_suspend_exit(void)
-{
- if (!system_supports_mte())
- return;
-
- sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, gcr_kernel_excl);
- isb();
-}
-
long set_mte_ctrl(struct task_struct *task, unsigned long arg)
{
u64 mte_ctrl = (~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &