arch/arm64/kernel/sdei.c

   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/stacktrace.h>
  17 #include <asm/sysreg.h>
  18 #include <asm/vmap_stack.h>
  19
  20 unsigned long sdei_exit_mode;
  21
  22 /*
  23  * VMAP'd stacks checking for stack overflow on exception using sp as a scratch
  24  * register, meaning SDEI has to switch to its own stack. We need two stacks as
  25  * a critical event may interrupt a normal event that has just taken a
  26  * synchronous exception, and is using sp as scratch register. For a critical
  27  * event interrupting a normal event, we can't reliably tell if we were on the
  28  * sdei stack.
  29  * For now, we allocate stacks when the driver is probed.
  30  */
  31 DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
  32 DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
  33
  34 #ifdef CONFIG_VMAP_STACK
  35 DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
  36 DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
  37 #endif
  38
  39 static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
  40 {
  41         unsigned long *p;
  42
  43         p = per_cpu(*ptr, cpu);
  44         if (p) {
  45                 per_cpu(*ptr, cpu) = NULL;
  46                 vfree(p);
  47         }
  48 }
  49
  50 static void free_sdei_stacks(void)
  51 {
  52         int cpu;
  53
  54         for_each_possible_cpu(cpu) {
  55                 _free_sdei_stack(&sdei_stack_normal_ptr, cpu);
  56                 _free_sdei_stack(&sdei_stack_critical_ptr, cpu);
  57         }
  58 }
  59
  60 static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
  61 {
  62         unsigned long *p;
  63
  64         p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
  65         if (!p)
  66                 return -ENOMEM;
  67         per_cpu(*ptr, cpu) = p;
  68
  69         return 0;
  70 }
  71
  72 static int init_sdei_stacks(void)
  73 {
  74         int cpu;
  75         int err = 0;
  76
  77         for_each_possible_cpu(cpu) {
  78                 err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
  79                 if (err)
  80                         break;
  81                 err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
  82                 if (err)
  83                         break;
  84         }
  85
  86         if (err)
  87                 free_sdei_stacks();
  88
  89         return err;
  90 }
  91
  92 static bool on_sdei_normal_stack(unsigned long sp, struct stack_info *info)
  93 {
  94         unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_normal_ptr);
  95         unsigned long high = low + SDEI_STACK_SIZE;
  96
  97         if (!low)
  98                 return false;
  99
 100         if (sp < low || sp >= high)
 101                 return false;
 102
 103         if (info) {
 104                 info->low = low;
 105                 info->high = high;
 106                 info->type = STACK_TYPE_SDEI_NORMAL;
 107         }
 108
 109         return true;
 110 }
 111
 112 static bool on_sdei_critical_stack(unsigned long sp, struct stack_info *info)
 113 {
 114         unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_critical_ptr);
 115         unsigned long high = low + SDEI_STACK_SIZE;
 116
 117         if (!low)
 118                 return false;
 119
 120         if (sp < low || sp >= high)
 121                 return false;
 122
 123         if (info) {
 124                 info->low = low;
 125                 info->high = high;
 126                 info->type = STACK_TYPE_SDEI_CRITICAL;
 127         }
 128
 129         return true;
 130 }
 131
 132 bool _on_sdei_stack(unsigned long sp, struct stack_info *info)
 133 {
 134         if (!IS_ENABLED(CONFIG_VMAP_STACK))
 135                 return false;
 136
 137         if (on_sdei_critical_stack(sp, info))
 138                 return true;
 139
 140         if (on_sdei_normal_stack(sp, info))
 141                 return true;
 142
 143         return false;
 144 }
 145
 146 unsigned long sdei_arch_get_entry_point(int conduit)
 147 {
 148         /*
 149          * SDEI works between adjacent exception levels. If we booted at EL1 we
 150          * assume a hypervisor is marshalling events. If we booted at EL2 and
 151          * dropped to EL1 because we don't support VHE, then we can't support
 152          * SDEI.
 153          */
 154         if (is_hyp_mode_available() && !is_kernel_in_hyp_mode()) {
 155                 pr_err("Not supported on this hardware/boot configuration\n");
 156                 return 0;
 157         }
 158
 159         if (IS_ENABLED(CONFIG_VMAP_STACK)) {
 160                 if (init_sdei_stacks())
 161                         return 0;
 162         }
 163
 164         sdei_exit_mode = (conduit == CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
 165
 166 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 167         if (arm64_kernel_unmapped_at_el0()) {
 168                 unsigned long offset;
 169
 170                 offset = (unsigned long)__sdei_asm_entry_trampoline -
 171                          (unsigned long)__entry_tramp_text_start;
 172                 return TRAMP_VALIAS + offset;
 173         } else
 174 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 175                 return (unsigned long)__sdei_asm_handler;
 176
 177 }
 178
 179 /*
 180  * __sdei_handler() returns one of:
 181  *  SDEI_EV_HANDLED -  success, return to the interrupted context.
 182  *  SDEI_EV_FAILED  -  failure, return this error code to firmare.
 183  *  virtual-address -  success, return to this address.
 184  */
 185 static __kprobes unsigned long _sdei_handler(struct pt_regs *regs,
 186                                              struct sdei_registered_event *arg)
 187 {
 188         u32 mode;
 189         int i, err = 0;
 190         int clobbered_registers = 4;
 191         u64 elr = read_sysreg(elr_el1);
 192         u32 kernel_mode = read_sysreg(CurrentEL) | 1;   /* +SPSel */
 193         unsigned long vbar = read_sysreg(vbar_el1);
 194
 195         if (arm64_kernel_unmapped_at_el0())
 196                 clobbered_registers++;
 197
 198         /* Retrieve the missing registers values */
 199         for (i = 0; i < clobbered_registers; i++) {
 200                 /* from within the handler, this call always succeeds */
 201                 sdei_api_event_context(i, &regs->regs[i]);
 202         }
 203
 204         /*
 205          * We didn't take an exception to get here, set PAN. UAO will be cleared
 206          * by sdei_event_handler()s set_fs(USER_DS) call.
 207          */
 208         __uaccess_enable_hw_pan();
 209
 210         err = sdei_event_handler(regs, arg);
 211         if (err)
 212                 return SDEI_EV_FAILED;
 213
 214         if (elr != read_sysreg(elr_el1)) {
 215                 /*
 216                  * We took a synchronous exception from the SDEI handler.
 217                  * This could deadlock, and if you interrupt KVM it will
 218                  * hyp-panic instead.
 219                  */
 220                 pr_warn("unsafe: exception during handler\n");
 221         }
 222
 223         mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);
 224
 225         /*
 226          * If we interrupted the kernel with interrupts masked, we always go
 227          * back to wherever we came from.
 228          */
 229         if (mode == kernel_mode && !interrupts_enabled(regs))
 230                 return SDEI_EV_HANDLED;
 231
 232         /*
 233          * Otherwise, we pretend this was an IRQ. This lets user space tasks
 234          * receive signals before we return to them, and KVM to invoke it's
 235          * world switch to do the same.
 236          *
 237          * See DDI0487B.a Table D1-7 'Vector offsets from vector table base
 238          * address'.
 239          */
 240         if (mode == kernel_mode)
 241                 return vbar + 0x280;
 242         else if (mode & PSR_MODE32_BIT)
 243                 return vbar + 0x680;
 244
 245         return vbar + 0x480;
 246 }
 247
 248
 249 asmlinkage __kprobes notrace unsigned long
 250 __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
 251 {
 252         unsigned long ret;
 253         bool do_nmi_exit = false;
 254
 255         /*
 256          * nmi_enter() deals with printk() re-entrance and use of RCU when
 257          * RCU believed this CPU was idle. Because critical events can
 258          * interrupt normal events, we may already be in_nmi().
 259          */
 260         if (!in_nmi()) {
 261                 nmi_enter();
 262                 do_nmi_exit = true;
 263         }
 264
 265         ret = _sdei_handler(regs, arg);
 266
 267         if (do_nmi_exit)
 268                 nmi_exit();
 269
 270         return ret;
 271 }