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Date: Mon, 18 Jan 2021 18:30:32 +0000 From: Vincenzo Frascino <vincenzo.frascino@....com> To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com Cc: Vincenzo Frascino <vincenzo.frascino@....com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Dmitry Vyukov <dvyukov@...gle.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>, Evgenii Stepanov <eugenis@...gle.com>, Branislav Rankov <Branislav.Rankov@....com>, Andrey Konovalov <andreyknvl@...gle.com> Subject: [PATCH v4 4/5] 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: Catalin Marinas <catalin.marinas@....com> Cc: Will Deacon <will@...nel.org> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com> --- arch/arm64/include/asm/mte.h | 32 ++++++++++++++++++++++ arch/arm64/kernel/entry-common.c | 6 ++++ arch/arm64/kernel/mte.c | 47 ++++++++++++++++++++++++++++++++ 3 files changed, 85 insertions(+) diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index d02aff9f493d..237bb2f7309d 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -92,5 +92,37 @@ static inline void mte_assign_mem_tag_range(void *addr, size_t size) #endif /* CONFIG_ARM64_MTE */ +#ifdef CONFIG_KASAN_HW_TAGS +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 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__ */ #endif /* __ASM_MTE_H */ diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 5346953e4382..31666511ba67 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(); @@ -243,6 +247,8 @@ 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 78fc079a3b1e..0a9cc82a5301 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -170,6 +170,44 @@ void mte_enable_kernel_async(void) __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); } +#ifdef CONFIG_KASAN_HW_TAGS +static inline void mte_report_async(void) +{ + u64 pc = (u64)__builtin_return_address(0); + + kasan_report_async(0, 0, false, pc); +} + +void mte_check_tfsr_el1(void) +{ + u64 tfsr_el1; + + if (!system_supports_mte()) + return; + + tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1); + + /* + * The kernel should never trigger an asynchronous fault on a + * TTBR0 address, so we should never see TF0 set. + * For futexes we disable checks via PSTATE.TCO. + */ + WARN_ONCE(tfsr_el1 & SYS_TFSR_EL1_TF0, + "Kernel async tag fault on TTBR0 address"); + + 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); + + mte_report_async(); + } +} +#endif + static void update_sctlr_el1_tcf0(u64 tcf0) { /* ISB required for the kernel uaccess routines */ @@ -235,6 +273,15 @@ 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); + + /* + * 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. + */ + mte_check_tfsr_el1(); } void mte_suspend_exit(void) -- 2.30.0
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