From 55b0b347918b1f9e8c7e8ae8cd057a9fddfffb0a Mon Sep 17 00:00:00 2001 From: Peter Collingbourne Date: Thu, 23 Sep 2021 18:06:55 -0700 Subject: [PATCH] FROMGIT: arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled 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 Acked-by: Andrey Konovalov Link: https://linux-review.googlesource.com/id/I78e90d60612a94c24344526f476ac4ff216e10d2 Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20210924010655.2886918-1-pcc@google.com Signed-off-by: Will Deacon (cherry picked from commit e5af50a5df571c1d0268b02f924de49b742c990f https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/mte) Change-Id: I0f06de2fce4dea2967c0fee608d1900915493d23 Bug: 192536783 --- arch/arm64/kernel/entry.S | 10 +++++----- arch/arm64/kernel/mte.c | 26 ++++++++++++++++++++++++++ include/linux/kasan.h | 9 +++++++-- 3 files changed, 38 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index ae1ded4ab618..42c404d508ca 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -193,9 +193,9 @@ 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: @@ -203,10 +203,10 @@ 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 66ae6698c5e1..acd43c57d9a0 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -183,6 +183,30 @@ static void mte_update_sctlr_user(struct task_struct *task) task->thread.sctlr_user = sctlr; } +static void mte_update_gcr_excl(struct task_struct *task) +{ + /* + * 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()) + return; + + write_sysreg_s( + ((task->thread.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) { if (!system_supports_mte()) @@ -202,6 +226,7 @@ void mte_thread_switch(struct task_struct *next) return; mte_update_sctlr_user(next); + mte_update_gcr_excl(next); /* * Check if an async tag exception occurred at EL1. @@ -247,6 +272,7 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg) if (task == current) { preempt_disable(); mte_update_sctlr_user(task); + mte_update_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 a1c7ce5f3e4f..b59675cc19b7 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 {