From: Will Deacon will.deacon@arm.com
commit 969f5ea627570e91c9d54403287ee3ed657f58fe upstream.
Revisions of the Cortex-A76 CPU prior to r4p0 are affected by an erratum that can prevent interrupts from being taken when single-stepping.
This patch implements a software workaround to prevent userspace from effectively being able to disable interrupts.
Cc: stable@vger.kernel.org Cc: Marc Zyngier marc.zyngier@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- Documentation/arm64/silicon-errata.txt | 1 arch/arm64/Kconfig | 18 ++++++++++++++++ arch/arm64/include/asm/cpucaps.h | 3 +- arch/arm64/kernel/cpu_errata.c | 24 +++++++++++++++++++++ arch/arm64/kernel/syscall.c | 31 +++++++++++++++++++++++++++ arch/arm64/mm/fault.c | 37 +++++++++++++++++++++++++++++++-- 6 files changed, 111 insertions(+), 3 deletions(-)
--- a/Documentation/arm64/silicon-errata.txt +++ b/Documentation/arm64/silicon-errata.txt @@ -61,6 +61,7 @@ stable kernels. | ARM | Cortex-A76 | #1188873 | ARM64_ERRATUM_1188873 | | ARM | Cortex-A76 | #1165522 | ARM64_ERRATUM_1165522 | | ARM | Cortex-A76 | #1286807 | ARM64_ERRATUM_1286807 | +| ARM | Cortex-A76 | #1463225 | ARM64_ERRATUM_1463225 | | ARM | MMU-500 | #841119,#826419 | N/A | | | | | | | Cavium | ThunderX ITS | #22375, #24313 | CAVIUM_ERRATUM_22375 | --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -517,6 +517,24 @@ config ARM64_ERRATUM_1286807
If unsure, say Y.
+config ARM64_ERRATUM_1463225 + bool "Cortex-A76: Software Step might prevent interrupt recognition" + default y + help + This option adds a workaround for Arm Cortex-A76 erratum 1463225. + + On the affected Cortex-A76 cores (r0p0 to r3p1), software stepping + of a system call instruction (SVC) can prevent recognition of + subsequent interrupts when software stepping is disabled in the + exception handler of the system call and either kernel debugging + is enabled or VHE is in use. + + Work around the erratum by triggering a dummy step exception + when handling a system call from a task that is being stepped + in a VHE configuration of the kernel. + + If unsure, say Y. + config CAVIUM_ERRATUM_22375 bool "Cavium erratum 22375, 24313" default y --- a/arch/arm64/include/asm/cpucaps.h +++ b/arch/arm64/include/asm/cpucaps.h @@ -61,7 +61,8 @@ #define ARM64_HAS_GENERIC_AUTH_ARCH 40 #define ARM64_HAS_GENERIC_AUTH_IMP_DEF 41 #define ARM64_HAS_IRQ_PRIO_MASKING 42 +#define ARM64_WORKAROUND_1463225 43
-#define ARM64_NCAPS 43 +#define ARM64_NCAPS 44
#endif /* __ASM_CPUCAPS_H */ --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -464,6 +464,22 @@ out_printmsg: } #endif /* CONFIG_ARM64_SSBD */
+#ifdef CONFIG_ARM64_ERRATUM_1463225 +DEFINE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); + +static bool +has_cortex_a76_erratum_1463225(const struct arm64_cpu_capabilities *entry, + int scope) +{ + u32 midr = read_cpuid_id(); + /* Cortex-A76 r0p0 - r3p1 */ + struct midr_range range = MIDR_RANGE(MIDR_CORTEX_A76, 0, 0, 3, 1); + + WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); + return is_midr_in_range(midr, &range) && is_kernel_in_hyp_mode(); +} +#endif + static void __maybe_unused cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused) { @@ -739,6 +755,14 @@ const struct arm64_cpu_capabilities arm6 ERRATA_MIDR_RANGE(MIDR_CORTEX_A76, 0, 0, 2, 0), }, #endif +#ifdef CONFIG_ARM64_ERRATUM_1463225 + { + .desc = "ARM erratum 1463225", + .capability = ARM64_WORKAROUND_1463225, + .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, + .matches = has_cortex_a76_erratum_1463225, + }, +#endif { } }; --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -8,6 +8,7 @@ #include <linux/syscalls.h>
#include <asm/daifflags.h> +#include <asm/debug-monitors.h> #include <asm/fpsimd.h> #include <asm/syscall.h> #include <asm/thread_info.h> @@ -60,6 +61,35 @@ static inline bool has_syscall_work(unsi int syscall_trace_enter(struct pt_regs *regs); void syscall_trace_exit(struct pt_regs *regs);
+#ifdef CONFIG_ARM64_ERRATUM_1463225 +DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); + +static void cortex_a76_erratum_1463225_svc_handler(void) +{ + u32 reg, val; + + if (!unlikely(test_thread_flag(TIF_SINGLESTEP))) + return; + + if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225))) + return; + + __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1); + reg = read_sysreg(mdscr_el1); + val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE; + write_sysreg(val, mdscr_el1); + asm volatile("msr daifclr, #8"); + isb(); + + /* We will have taken a single-step exception by this point */ + + write_sysreg(reg, mdscr_el1); + __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0); +} +#else +static void cortex_a76_erratum_1463225_svc_handler(void) { } +#endif /* CONFIG_ARM64_ERRATUM_1463225 */ + static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, const syscall_fn_t syscall_table[]) { @@ -68,6 +98,7 @@ static void el0_svc_common(struct pt_reg regs->orig_x0 = regs->regs[0]; regs->syscallno = scno;
+ cortex_a76_erratum_1463225_svc_handler(); local_daif_restore(DAIF_PROCCTX); user_exit();
--- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -810,14 +810,47 @@ void __init hook_debug_fault_code(int nr debug_fault_info[nr].name = name; }
+#ifdef CONFIG_ARM64_ERRATUM_1463225 +DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); + +static int __exception +cortex_a76_erratum_1463225_debug_handler(struct pt_regs *regs) +{ + if (user_mode(regs)) + return 0; + + if (!__this_cpu_read(__in_cortex_a76_erratum_1463225_wa)) + return 0; + + /* + * We've taken a dummy step exception from the kernel to ensure + * that interrupts are re-enabled on the syscall path. Return back + * to cortex_a76_erratum_1463225_svc_handler() with debug exceptions + * masked so that we can safely restore the mdscr and get on with + * handling the syscall. + */ + regs->pstate |= PSR_D_BIT; + return 1; +} +#else +static int __exception +cortex_a76_erratum_1463225_debug_handler(struct pt_regs *regs) +{ + return 0; +} +#endif /* CONFIG_ARM64_ERRATUM_1463225 */ + asmlinkage int __exception do_debug_exception(unsigned long addr_if_watchpoint, - unsigned int esr, - struct pt_regs *regs) + unsigned int esr, + struct pt_regs *regs) { const struct fault_info *inf = esr_to_debug_fault_info(esr); unsigned long pc = instruction_pointer(regs); int rv;
+ if (cortex_a76_erratum_1463225_debug_handler(regs)) + return 0; + /* * Tell lockdep we disabled irqs in entry.S. Do nothing if they were * already disabled to preserve the last enabled/disabled addresses.