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Message-Id: <20210315132019.33202-8-vincenzo.frascino@arm.com>
Date: Mon, 15 Mar 2021 13:20:17 +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>,
Andrew Morton <akpm@...ux-foundation.org>,
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>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: [PATCH v16 7/9] 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>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Acked-by: Andrey Konovalov <andreyknvl@...gle.com>
Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
---
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)
--
2.30.2
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