1 // SPDX-License-Identifier: GPL-2.0 2 // Copyright (C) 2017 Arm Ltd. 3 #define pr_fmt(fmt) "sdei: " fmt 4 5 #include <linux/arm_sdei.h> 6 #include <linux/hardirq.h> 7 #include <linux/irqflags.h> 8 #include <linux/sched/task_stack.h> 9 #include <linux/uaccess.h> 10 11 #include <asm/alternative.h> 12 #include <asm/kprobes.h> 13 #include <asm/mmu.h> 14 #include <asm/ptrace.h> 15 #include <asm/sections.h> 16 #include <asm/sysreg.h> 17 #include <asm/vmap_stack.h> 18 19 unsigned long sdei_exit_mode; 20 21 /* 22 * VMAP'd stacks checking for stack overflow on exception using sp as a scratch 23 * register, meaning SDEI has to switch to its own stack. We need two stacks as 24 * a critical event may interrupt a normal event that has just taken a 25 * synchronous exception, and is using sp as scratch register. For a critical 26 * event interrupting a normal event, we can't reliably tell if we were on the 27 * sdei stack. 28 * For now, we allocate stacks when the driver is probed. 29 */ 30 DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr); 31 DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr); 32 33 #ifdef CONFIG_VMAP_STACK 34 DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr); 35 DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr); 36 #endif 37 38 static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu) 39 { 40 unsigned long *p; 41 42 p = per_cpu(*ptr, cpu); 43 if (p) { 44 per_cpu(*ptr, cpu) = NULL; 45 vfree(p); 46 } 47 } 48 49 static void free_sdei_stacks(void) 50 { 51 int cpu; 52 53 for_each_possible_cpu(cpu) { 54 _free_sdei_stack(&sdei_stack_normal_ptr, cpu); 55 _free_sdei_stack(&sdei_stack_critical_ptr, cpu); 56 } 57 } 58 59 static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu) 60 { 61 unsigned long *p; 62 63 p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu)); 64 if (!p) 65 return -ENOMEM; 66 per_cpu(*ptr, cpu) = p; 67 68 return 0; 69 } 70 71 static int init_sdei_stacks(void) 72 { 73 int cpu; 74 int err = 0; 75 76 for_each_possible_cpu(cpu) { 77 err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu); 78 if (err) 79 break; 80 err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu); 81 if (err) 82 break; 83 } 84 85 if (err) 86 free_sdei_stacks(); 87 88 return err; 89 } 90 91 bool _on_sdei_stack(unsigned long sp) 92 { 93 unsigned long low, high; 94 95 if (!IS_ENABLED(CONFIG_VMAP_STACK)) 96 return false; 97 98 low = (unsigned long)raw_cpu_read(sdei_stack_critical_ptr); 99 high = low + SDEI_STACK_SIZE; 100 101 if (low <= sp && sp < high) 102 return true; 103 104 low = (unsigned long)raw_cpu_read(sdei_stack_normal_ptr); 105 high = low + SDEI_STACK_SIZE; 106 107 return (low <= sp && sp < high); 108 } 109 110 unsigned long sdei_arch_get_entry_point(int conduit) 111 { 112 /* 113 * SDEI works between adjacent exception levels. If we booted at EL1 we 114 * assume a hypervisor is marshalling events. If we booted at EL2 and 115 * dropped to EL1 because we don't support VHE, then we can't support 116 * SDEI. 117 */ 118 if (is_hyp_mode_available() && !is_kernel_in_hyp_mode()) { 119 pr_err("Not supported on this hardware/boot configuration\n"); 120 return 0; 121 } 122 123 if (IS_ENABLED(CONFIG_VMAP_STACK)) { 124 if (init_sdei_stacks()) 125 return 0; 126 } 127 128 sdei_exit_mode = (conduit == CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC; 129 130 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0 131 if (arm64_kernel_unmapped_at_el0()) { 132 unsigned long offset; 133 134 offset = (unsigned long)__sdei_asm_entry_trampoline - 135 (unsigned long)__entry_tramp_text_start; 136 return TRAMP_VALIAS + offset; 137 } else 138 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */ 139 return (unsigned long)__sdei_asm_handler; 140 141 } 142 143 /* 144 * __sdei_handler() returns one of: 145 * SDEI_EV_HANDLED - success, return to the interrupted context. 146 * SDEI_EV_FAILED - failure, return this error code to firmare. 147 * virtual-address - success, return to this address. 148 */ 149 static __kprobes unsigned long _sdei_handler(struct pt_regs *regs, 150 struct sdei_registered_event *arg) 151 { 152 u32 mode; 153 int i, err = 0; 154 int clobbered_registers = 4; 155 u64 elr = read_sysreg(elr_el1); 156 u32 kernel_mode = read_sysreg(CurrentEL) | 1; /* +SPSel */ 157 unsigned long vbar = read_sysreg(vbar_el1); 158 159 if (arm64_kernel_unmapped_at_el0()) 160 clobbered_registers++; 161 162 /* Retrieve the missing registers values */ 163 for (i = 0; i < clobbered_registers; i++) { 164 /* from within the handler, this call always succeeds */ 165 sdei_api_event_context(i, ®s->regs[i]); 166 } 167 168 /* 169 * We didn't take an exception to get here, set PAN. UAO will be cleared 170 * by sdei_event_handler()s set_fs(USER_DS) call. 171 */ 172 __uaccess_enable_hw_pan(); 173 174 err = sdei_event_handler(regs, arg); 175 if (err) 176 return SDEI_EV_FAILED; 177 178 if (elr != read_sysreg(elr_el1)) { 179 /* 180 * We took a synchronous exception from the SDEI handler. 181 * This could deadlock, and if you interrupt KVM it will 182 * hyp-panic instead. 183 */ 184 pr_warn("unsafe: exception during handler\n"); 185 } 186 187 mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK); 188 189 /* 190 * If we interrupted the kernel with interrupts masked, we always go 191 * back to wherever we came from. 192 */ 193 if (mode == kernel_mode && !interrupts_enabled(regs)) 194 return SDEI_EV_HANDLED; 195 196 /* 197 * Otherwise, we pretend this was an IRQ. This lets user space tasks 198 * receive signals before we return to them, and KVM to invoke it's 199 * world switch to do the same. 200 * 201 * See DDI0487B.a Table D1-7 'Vector offsets from vector table base 202 * address'. 203 */ 204 if (mode == kernel_mode) 205 return vbar + 0x280; 206 else if (mode & PSR_MODE32_BIT) 207 return vbar + 0x680; 208 209 return vbar + 0x480; 210 } 211 212 213 asmlinkage __kprobes notrace unsigned long 214 __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg) 215 { 216 unsigned long ret; 217 bool do_nmi_exit = false; 218 219 /* 220 * nmi_enter() deals with printk() re-entrance and use of RCU when 221 * RCU believed this CPU was idle. Because critical events can 222 * interrupt normal events, we may already be in_nmi(). 223 */ 224 if (!in_nmi()) { 225 nmi_enter(); 226 do_nmi_exit = true; 227 } 228 229 ret = _sdei_handler(regs, arg); 230 231 if (do_nmi_exit) 232 nmi_exit(); 233 234 return ret; 235 } 236