diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index c5cd2c599b24e905e3ff8abcae1edc109960b33a..1a025b7441077d476a30b55c4596a8605156736c 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -133,6 +133,8 @@ #define IRQ_STACK_SIZE THREAD_SIZE +#define OVERFLOW_STACK_SIZE SZ_4K + /* * Alignment of kernel segments (e.g. .text, .data). */ diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 92ddb6d25cf3235f2c385aefbe6de61e3ce0aee9..6ad30776e984d071134f8762395565859691e0b0 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -57,6 +57,20 @@ static inline bool on_task_stack(struct task_struct *tsk, unsigned long sp) return (low <= sp && sp < high); } +#ifdef CONFIG_VMAP_STACK +DECLARE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack); + +static inline bool on_overflow_stack(unsigned long sp) +{ + unsigned long low = (unsigned long)raw_cpu_ptr(overflow_stack); + unsigned long high = low + OVERFLOW_STACK_SIZE; + + return (low <= sp && sp < high); +} +#else +static inline bool on_overflow_stack(unsigned long sp) { return false; } +#endif + /* * We can only safely access per-cpu stacks from current in a non-preemptible * context. @@ -69,6 +83,8 @@ static inline bool on_accessible_stack(struct task_struct *tsk, unsigned long sp return false; if (on_irq_stack(sp)) return true; + if (on_overflow_stack(sp)) + return true; return false; } diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 52348869f82f2e8e32e70226c1f3c84bb83c5e89..3ef6e2297fb4048c22ea99df37d42d9599b2b009 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -72,6 +72,48 @@ .macro kernel_ventry label .align 7 sub sp, sp, #S_FRAME_SIZE +#ifdef CONFIG_VMAP_STACK + /* + * Test whether the SP has overflowed, without corrupting a GPR. + * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT). + */ + add sp, sp, x0 // sp' = sp + x0 + sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp + tbnz x0, #THREAD_SHIFT, 0f + sub x0, sp, x0 // x0'' = sp' - x0' = (sp + x0) - sp = x0 + sub sp, sp, x0 // sp'' = sp' - x0 = (sp + x0) - x0 = sp + b \label + +0: + /* + * Either we've just detected an overflow, or we've taken an exception + * while on the overflow stack. Either way, we won't return to + * userspace, and can clobber EL0 registers to free up GPRs. + */ + + /* Stash the original SP (minus S_FRAME_SIZE) in tpidr_el0. */ + msr tpidr_el0, x0 + + /* Recover the original x0 value and stash it in tpidrro_el0 */ + sub x0, sp, x0 + msr tpidrro_el0, x0 + + /* Switch to the overflow stack */ + adr_this_cpu sp, overflow_stack + OVERFLOW_STACK_SIZE, x0 + + /* + * Check whether we were already on the overflow stack. This may happen + * after panic() re-enables interrupts. + */ + mrs x0, tpidr_el0 // sp of interrupted context + sub x0, sp, x0 // delta with top of overflow stack + tst x0, #~(OVERFLOW_STACK_SIZE - 1) // within range? + b.ne __bad_stack // no? -> bad stack pointer + + /* We were already on the overflow stack. Restore sp/x0 and carry on. */ + sub sp, sp, x0 + mrs x0, tpidrro_el0 +#endif b \label .endm @@ -352,6 +394,34 @@ ENTRY(vectors) #endif END(vectors) +#ifdef CONFIG_VMAP_STACK + /* + * We detected an overflow in kernel_ventry, which switched to the + * overflow stack. Stash the exception regs, and head to our overflow + * handler. + */ +__bad_stack: + /* Restore the original x0 value */ + mrs x0, tpidrro_el0 + + /* + * Store the original GPRs to the new stack. The orginal SP (minus + * S_FRAME_SIZE) was stashed in tpidr_el0 by kernel_ventry. + */ + sub sp, sp, #S_FRAME_SIZE + kernel_entry 1 + mrs x0, tpidr_el0 + add x0, x0, #S_FRAME_SIZE + str x0, [sp, #S_SP] + + /* Stash the regs for handle_bad_stack */ + mov x0, sp + + /* Time to die */ + bl handle_bad_stack + ASM_BUG() +#endif /* CONFIG_VMAP_STACK */ + /* * Invalid mode handlers */ diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index d01c5988354b1e178834c054e0e2339edad4d7ff..2d591804e46fc46c737355476c5826eae392b89f 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -32,6 +32,7 @@ #include #include #include +#include #include #include @@ -41,6 +42,7 @@ #include #include #include +#include #include #include #include @@ -666,6 +668,43 @@ asmlinkage void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr) force_sig_info(info.si_signo, &info, current); } +#ifdef CONFIG_VMAP_STACK + +DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack) + __aligned(16); + +asmlinkage void handle_bad_stack(struct pt_regs *regs) +{ + unsigned long tsk_stk = (unsigned long)current->stack; + unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr); + unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack); + unsigned int esr = read_sysreg(esr_el1); + unsigned long far = read_sysreg(far_el1); + + console_verbose(); + pr_emerg("Insufficient stack space to handle exception!"); + + pr_emerg("ESR: 0x%08x -- %s\n", esr, esr_get_class_string(esr)); + pr_emerg("FAR: 0x%016lx\n", far); + + pr_emerg("Task stack: [0x%016lx..0x%016lx]\n", + tsk_stk, tsk_stk + THREAD_SIZE); + pr_emerg("IRQ stack: [0x%016lx..0x%016lx]\n", + irq_stk, irq_stk + THREAD_SIZE); + pr_emerg("Overflow stack: [0x%016lx..0x%016lx]\n", + ovf_stk, ovf_stk + OVERFLOW_STACK_SIZE); + + __show_regs(regs); + + /* + * We use nmi_panic to limit the potential for recusive overflows, and + * to get a better stack trace. + */ + nmi_panic(NULL, "kernel stack overflow"); + cpu_park_loop(); +} +#endif + void __pte_error(const char *file, int line, unsigned long val) { pr_err("%s:%d: bad pte %016lx.\n", file, line, val);