From 65812c6921cc849d86811147038dd246fa0ea18c Mon Sep 17 00:00:00 2001 From: Vincenzo Frascino Date: Mon, 15 Mar 2021 13:20:17 +0000 Subject: [PATCH] arm64: mte: Enable async tag check fault MTE provides a mode that asynchronously updates the TFSR_EL1 register when a tag check exception is detected. To take advantage of this mode the kernel has to verify the status of the register at: 1. Context switching 2. Return to user/EL0 (Not required in entry from EL0 since the kernel did not run) 3. Kernel entry from EL1 4. Kernel exit to EL1 If the register is non-zero a trace is reported. Add the required features for EL1 detection and reporting. Note: ITFSB bit is set in the SCTLR_EL1 register hence it guaranties that the indirect writes to TFSR_EL1 are synchronized at exception entry to EL1. On the context switch path the synchronization is guarantied by the dsb() in __switch_to(). The dsb(nsh) in mte_check_tfsr_exit() is provisional pending confirmation by the architects. Cc: Will Deacon Reviewed-by: Catalin Marinas Acked-by: Andrey Konovalov Tested-by: Andrey Konovalov Signed-off-by: Vincenzo Frascino Link: https://lore.kernel.org/r/20210315132019.33202-8-vincenzo.frascino@arm.com Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/mte.h | 29 +++++++++++++++++++++++++ arch/arm64/kernel/entry-common.c | 6 ++++++ arch/arm64/kernel/mte.c | 36 ++++++++++++++++++++++++++++++++ 3 files changed, 71 insertions(+) diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index 8603c6636a7d..9a929620ca5d 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -98,11 +98,40 @@ static inline bool system_uses_mte_async_mode(void) { return static_branch_unlikely(&mte_async_mode); } + +void mte_check_tfsr_el1(void); + +static inline void mte_check_tfsr_entry(void) +{ + mte_check_tfsr_el1(); +} + +static inline void mte_check_tfsr_exit(void) +{ + /* + * The asynchronous faults are sync'ed automatically with + * TFSR_EL1 on kernel entry but for exit an explicit dsb() + * is required. + */ + dsb(nsh); + isb(); + + mte_check_tfsr_el1(); +} #else static inline bool system_uses_mte_async_mode(void) { return false; } +static inline void mte_check_tfsr_el1(void) +{ +} +static inline void mte_check_tfsr_entry(void) +{ +} +static inline void mte_check_tfsr_exit(void) +{ +} #endif /* CONFIG_KASAN_HW_TAGS */ #endif /* __ASSEMBLY__ */ diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 9d3588450473..a1ec351c36bd 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -37,6 +37,8 @@ static void noinstr enter_from_kernel_mode(struct pt_regs *regs) lockdep_hardirqs_off(CALLER_ADDR0); rcu_irq_enter_check_tick(); trace_hardirqs_off_finish(); + + mte_check_tfsr_entry(); } /* @@ -47,6 +49,8 @@ static void noinstr exit_to_kernel_mode(struct pt_regs *regs) { lockdep_assert_irqs_disabled(); + mte_check_tfsr_exit(); + if (interrupts_enabled(regs)) { if (regs->exit_rcu) { trace_hardirqs_on_prepare(); @@ -293,6 +297,8 @@ asmlinkage void noinstr enter_from_user_mode(void) asmlinkage void noinstr exit_to_user_mode(void) { + mte_check_tfsr_exit(); + trace_hardirqs_on_prepare(); lockdep_hardirqs_on_prepare(CALLER_ADDR0); user_enter_irqoff(); diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index 50f0724c8d8f..b6336fbe4c14 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -162,6 +162,29 @@ bool mte_report_once(void) return READ_ONCE(report_fault_once); } +#ifdef CONFIG_KASAN_HW_TAGS +void mte_check_tfsr_el1(void) +{ + u64 tfsr_el1; + + if (!system_supports_mte()) + return; + + tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1); + + if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) { + /* + * Note: isb() is not required after this direct write + * because there is no indirect read subsequent to it + * (per ARM DDI 0487F.c table D13-1). + */ + write_sysreg_s(0, SYS_TFSR_EL1); + + kasan_report_async(); + } +} +#endif + static void update_sctlr_el1_tcf0(u64 tcf0) { /* ISB required for the kernel uaccess routines */ @@ -227,6 +250,19 @@ void mte_thread_switch(struct task_struct *next) /* avoid expensive SCTLR_EL1 accesses if no change */ if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0) update_sctlr_el1_tcf0(next->thread.sctlr_tcf0); + else + isb(); + + /* + * Check if an async tag exception occurred at EL1. + * + * Note: On the context switch path we rely on the dsb() present + * in __switch_to() to guarantee that the indirect writes to TFSR_EL1 + * are synchronized before this point. + * isb() above is required for the same reason. + * + */ + mte_check_tfsr_el1(); } void mte_suspend_exit(void) -- 2.20.1