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-smccc.h>
   6 #include <linux/arm_sdei.h>
   7 #include <linux/hardirq.h>
   8 #include <linux/irqflags.h>
   9 #include <linux/sched/task_stack.h>
  10 #include <linux/scs.h>
  11 #include <linux/uaccess.h>
  12
  13 #include <asm/alternative.h>
  14 #include <asm/exception.h>
  15 #include <asm/kprobes.h>
  16 #include <asm/mmu.h>
  17 #include <asm/ptrace.h>
  18 #include <asm/sections.h>
  19 #include <asm/stacktrace.h>
  20 #include <asm/sysreg.h>
  21 #include <asm/vmap_stack.h>
  22
  23 unsigned long sdei_exit_mode;
  24
  25 /*
  26  * VMAP'd stacks checking for stack overflow on exception using sp as a scratch
  27  * register, meaning SDEI has to switch to its own stack. We need two stacks as
  28  * a critical event may interrupt a normal event that has just taken a
  29  * synchronous exception, and is using sp as scratch register. For a critical
  30  * event interrupting a normal event, we can't reliably tell if we were on the
  31  * sdei stack.
  32  * For now, we allocate stacks when the driver is probed.
  33  */
  34 DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
  35 DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
  36
  37 #ifdef CONFIG_VMAP_STACK
  38 DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
  39 DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
  40 #endif
  41
  42 DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr);
  43 DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr);
  44
  45 #ifdef CONFIG_SHADOW_CALL_STACK
  46 DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr);
  47 DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr);
  48 #endif
  49
  50 static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
  51 {
  52         unsigned long *p;
  53
  54         p = per_cpu(*ptr, cpu);
  55         if (p) {
  56                 per_cpu(*ptr, cpu) = NULL;
  57                 vfree(p);
  58         }
  59 }
  60
  61 static void free_sdei_stacks(void)
  62 {
  63         int cpu;
  64
  65         if (!IS_ENABLED(CONFIG_VMAP_STACK))
  66                 return;
  67
  68         for_each_possible_cpu(cpu) {
  69                 _free_sdei_stack(&sdei_stack_normal_ptr, cpu);
  70                 _free_sdei_stack(&sdei_stack_critical_ptr, cpu);
  71         }
  72 }
  73
  74 static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
  75 {
  76         unsigned long *p;
  77
  78         p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
  79         if (!p)
  80                 return -ENOMEM;
  81         per_cpu(*ptr, cpu) = p;
  82
  83         return 0;
  84 }
  85
  86 static int init_sdei_stacks(void)
  87 {
  88         int cpu;
  89         int err = 0;
  90
  91         if (!IS_ENABLED(CONFIG_VMAP_STACK))
  92                 return 0;
  93
  94         for_each_possible_cpu(cpu) {
  95                 err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
  96                 if (err)
  97                         break;
  98                 err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
  99                 if (err)
 100                         break;
 101         }
 102
 103         if (err)
 104                 free_sdei_stacks();
 105
 106         return err;
 107 }
 108
 109 static void _free_sdei_scs(unsigned long * __percpu *ptr, int cpu)
 110 {
 111         void *s;
 112
 113         s = per_cpu(*ptr, cpu);
 114         if (s) {
 115                 per_cpu(*ptr, cpu) = NULL;
 116                 scs_free(s);
 117         }
 118 }
 119
 120 static void free_sdei_scs(void)
 121 {
 122         int cpu;
 123
 124         for_each_possible_cpu(cpu) {
 125                 _free_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
 126                 _free_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
 127         }
 128 }
 129
 130 static int _init_sdei_scs(unsigned long * __percpu *ptr, int cpu)
 131 {
 132         void *s;
 133
 134         s = scs_alloc(cpu_to_node(cpu));
 135         if (!s)
 136                 return -ENOMEM;
 137         per_cpu(*ptr, cpu) = s;
 138
 139         return 0;
 140 }
 141
 142 static int init_sdei_scs(void)
 143 {
 144         int cpu;
 145         int err = 0;
 146
 147         if (!IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
 148                 return 0;
 149
 150         for_each_possible_cpu(cpu) {
 151                 err = _init_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
 152                 if (err)
 153                         break;
 154                 err = _init_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
 155                 if (err)
 156                         break;
 157         }
 158
 159         if (err)
 160                 free_sdei_scs();
 161
 162         return err;
 163 }
 164
 165 static bool on_sdei_normal_stack(unsigned long sp, struct stack_info *info)
 166 {
 167         unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_normal_ptr);
 168         unsigned long high = low + SDEI_STACK_SIZE;
 169
 170         return on_stack(sp, low, high, STACK_TYPE_SDEI_NORMAL, info);
 171 }
 172
 173 static bool on_sdei_critical_stack(unsigned long sp, struct stack_info *info)
 174 {
 175         unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_critical_ptr);
 176         unsigned long high = low + SDEI_STACK_SIZE;
 177
 178         return on_stack(sp, low, high, STACK_TYPE_SDEI_CRITICAL, info);
 179 }
 180
 181 bool _on_sdei_stack(unsigned long sp, struct stack_info *info)
 182 {
 183         if (!IS_ENABLED(CONFIG_VMAP_STACK))
 184                 return false;
 185
 186         if (on_sdei_critical_stack(sp, info))
 187                 return true;
 188
 189         if (on_sdei_normal_stack(sp, info))
 190                 return true;
 191
 192         return false;
 193 }
 194
 195 unsigned long sdei_arch_get_entry_point(int conduit)
 196 {
 197         /*
 198          * SDEI works between adjacent exception levels. If we booted at EL1 we
 199          * assume a hypervisor is marshalling events. If we booted at EL2 and
 200          * dropped to EL1 because we don't support VHE, then we can't support
 201          * SDEI.
 202          */
 203         if (is_hyp_mode_available() && !is_kernel_in_hyp_mode()) {
 204                 pr_err("Not supported on this hardware/boot configuration\n");
 205                 goto out_err;
 206         }
 207
 208         if (init_sdei_stacks())
 209                 goto out_err;
 210
 211         if (init_sdei_scs())
 212                 goto out_err_free_stacks;
 213
 214         sdei_exit_mode = (conduit == SMCCC_CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
 215
 216 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 217         if (arm64_kernel_unmapped_at_el0()) {
 218                 unsigned long offset;
 219
 220                 offset = (unsigned long)__sdei_asm_entry_trampoline -
 221                          (unsigned long)__entry_tramp_text_start;
 222                 return TRAMP_VALIAS + offset;
 223         } else
 224 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 225                 return (unsigned long)__sdei_asm_handler;
 226
 227 out_err_free_stacks:
 228         free_sdei_stacks();
 229 out_err:
 230         return 0;
 231 }
 232
 233 /*
 234  * __sdei_handler() returns one of:
 235  *  SDEI_EV_HANDLED -  success, return to the interrupted context.
 236  *  SDEI_EV_FAILED  -  failure, return this error code to firmare.
 237  *  virtual-address -  success, return to this address.
 238  */
 239 static __kprobes unsigned long _sdei_handler(struct pt_regs *regs,
 240                                              struct sdei_registered_event *arg)
 241 {
 242         u32 mode;
 243         int i, err = 0;
 244         int clobbered_registers = 4;
 245         u64 elr = read_sysreg(elr_el1);
 246         u32 kernel_mode = read_sysreg(CurrentEL) | 1;   /* +SPSel */
 247         unsigned long vbar = read_sysreg(vbar_el1);
 248
 249         if (arm64_kernel_unmapped_at_el0())
 250                 clobbered_registers++;
 251
 252         /* Retrieve the missing registers values */
 253         for (i = 0; i < clobbered_registers; i++) {
 254                 /* from within the handler, this call always succeeds */
 255                 sdei_api_event_context(i, &regs->regs[i]);
 256         }
 257
 258         err = sdei_event_handler(regs, arg);
 259         if (err)
 260                 return SDEI_EV_FAILED;
 261
 262         if (elr != read_sysreg(elr_el1)) {
 263                 /*
 264                  * We took a synchronous exception from the SDEI handler.
 265                  * This could deadlock, and if you interrupt KVM it will
 266                  * hyp-panic instead.
 267                  */
 268                 pr_warn("unsafe: exception during handler\n");
 269         }
 270
 271         mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);
 272
 273         /*
 274          * If we interrupted the kernel with interrupts masked, we always go
 275          * back to wherever we came from.
 276          */
 277         if (mode == kernel_mode && !interrupts_enabled(regs))
 278                 return SDEI_EV_HANDLED;
 279
 280         /*
 281          * Otherwise, we pretend this was an IRQ. This lets user space tasks
 282          * receive signals before we return to them, and KVM to invoke it's
 283          * world switch to do the same.
 284          *
 285          * See DDI0487B.a Table D1-7 'Vector offsets from vector table base
 286          * address'.
 287          */
 288         if (mode == kernel_mode)
 289                 return vbar + 0x280;
 290         else if (mode & PSR_MODE32_BIT)
 291                 return vbar + 0x680;
 292
 293         return vbar + 0x480;
 294 }
 295
 296 static void __kprobes notrace __sdei_pstate_entry(void)
 297 {
 298         /*
 299          * The original SDEI spec (ARM DEN 0054A) can be read ambiguously as to
 300          * whether PSTATE bits are inherited unchanged or generated from
 301          * scratch, and the TF-A implementation always clears PAN and always
 302          * clears UAO. There are no other known implementations.
 303          *
 304          * Subsequent revisions (ARM DEN 0054B) follow the usual rules for how
 305          * PSTATE is modified upon architectural exceptions, and so PAN is
 306          * either inherited or set per SCTLR_ELx.SPAN, and UAO is always
 307          * cleared.
 308          *
 309          * We must explicitly reset PAN to the expected state, including
 310          * clearing it when the host isn't using it, in case a VM had it set.
 311          */
 312         if (system_uses_hw_pan())
 313                 set_pstate_pan(1);
 314         else if (cpu_has_pan())
 315                 set_pstate_pan(0);
 316 }
 317
 318 asmlinkage noinstr unsigned long
 319 __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
 320 {
 321         unsigned long ret;
 322
 323         /*
 324          * We didn't take an exception to get here, so the HW hasn't
 325          * set/cleared bits in PSTATE that we may rely on. Initialize PAN.
 326          */
 327         __sdei_pstate_entry();
 328
 329         arm64_enter_nmi(regs);
 330
 331         ret = _sdei_handler(regs, arg);
 332
 333         arm64_exit_nmi(regs);
 334
 335         return ret;
 336 }