[PATCH v3 2/2] arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled
From: Peter Collingbourne <hidden>
Date: 2021-09-15 19:06:11
Subsystem:
arm64 port (aarch64 architecture), kasan, the rest · Maintainers:
Catalin Marinas, Will Deacon, Andrey Ryabinin, Linus Torvalds
It is not necessary to write to GCR_EL1 on every kernel entry and exit when HW tag-based KASAN is disabled because the kernel will not execute any IRG instructions in that mode. Since accessing GCR_EL1 can be expensive on some microarchitectures, avoid doing so by moving the access to task switch when HW tag-based KASAN is disabled. Signed-off-by: Peter Collingbourne <redacted> Acked-by: Andrey Konovalov <andreyknvl@gmail.com> Link: https://linux-review.googlesource.com/id/I78e90d60612a94c24344526f476ac4ff216e10d2 --- v2: - add prerequisite patch to fix booting on non-MTE hardware arch/arm64/kernel/entry.S | 10 +++++----- arch/arm64/kernel/mte.c | 24 +++++++++++++++++++++--- include/linux/kasan.h | 9 +++++++-- 3 files changed, 33 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index bc6d5a970a13..2f69ae43941d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S@@ -168,9 +168,9 @@ alternative_else_nop_endif .macro mte_set_kernel_gcr, tmp, tmp2 #ifdef CONFIG_KASAN_HW_TAGS -alternative_if_not ARM64_MTE +alternative_cb kasan_hw_tags_enable b 1f -alternative_else_nop_endif +alternative_cb_end mov \tmp, KERNEL_GCR_EL1 msr_s SYS_GCR_EL1, \tmp 1:
@@ -178,10 +178,10 @@ alternative_else_nop_endif .endm .macro mte_set_user_gcr, tsk, tmp, tmp2 -#ifdef CONFIG_ARM64_MTE -alternative_if_not ARM64_MTE +#ifdef CONFIG_KASAN_HW_TAGS +alternative_cb kasan_hw_tags_enable b 1f -alternative_else_nop_endif +alternative_cb_end ldr \tmp, [\tsk, #THREAD_MTE_CTRL] mte_set_gcr \tmp, \tmp2
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index e5e801bc5312..bb8204d4c5d3 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c@@ -157,7 +157,7 @@ void mte_check_tfsr_el1(void) } #endif -static void mte_update_sctlr_user(struct task_struct *task) +static void mte_update_sctlr_user_and_gcr_excl(struct task_struct *task) { /* * This must be called with preemption disabled and can only be called
@@ -177,6 +177,24 @@ static void mte_update_sctlr_user(struct task_struct *task) else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC) sctlr |= SCTLR_EL1_TCF0_SYNC; task->thread.sctlr_user = sctlr; + + /* + * SYS_GCR_EL1 will be set to current->thread.mte_ctrl value by + * mte_set_user_gcr() in kernel_exit, but only if KASAN is enabled. + */ + if (!kasan_hw_tags_enabled()) + write_sysreg_s(((mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) & + SYS_GCR_EL1_EXCL_MASK) | SYS_GCR_EL1_RRND, + SYS_GCR_EL1); +} + +void __init kasan_hw_tags_enable(struct alt_instr *alt, __le32 *origptr, + __le32 *updptr, int nr_inst) +{ + BUG_ON(nr_inst != 1); /* Branch -> NOP */ + + if (kasan_hw_tags_enabled()) + *updptr = cpu_to_le32(aarch64_insn_gen_nop()); } void mte_thread_init_user(void)
@@ -197,7 +215,7 @@ void mte_thread_switch(struct task_struct *next) if (!system_supports_mte()) return; - mte_update_sctlr_user(next); + mte_update_sctlr_user_and_gcr_excl(next); /* * Check if an async tag exception occurred at EL1.
@@ -242,7 +260,7 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg) task->thread.mte_ctrl = mte_ctrl; if (task == current) { preempt_disable(); - mte_update_sctlr_user(task); + mte_update_sctlr_user_and_gcr_excl(task); update_sctlr_el1(task->thread.sctlr_user); preempt_enable(); }
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index dd874a1ee862..de5f5913374d 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h@@ -89,7 +89,7 @@ static __always_inline bool kasan_enabled(void) return static_branch_likely(&kasan_flag_enabled); } -static inline bool kasan_has_integrated_init(void) +static inline bool kasan_hw_tags_enabled(void) { return kasan_enabled(); }
@@ -104,7 +104,7 @@ static inline bool kasan_enabled(void) return IS_ENABLED(CONFIG_KASAN); } -static inline bool kasan_has_integrated_init(void) +static inline bool kasan_hw_tags_enabled(void) { return false; }
@@ -125,6 +125,11 @@ static __always_inline void kasan_free_pages(struct page *page, #endif /* CONFIG_KASAN_HW_TAGS */ +static inline bool kasan_has_integrated_init(void) +{ + return kasan_hw_tags_enabled(); +} + #ifdef CONFIG_KASAN struct kasan_cache {
--
2.33.0.309.g3052b89438-goog
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