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/uaccess.h>
  11
  12 #include <asm/alternative.h>
  13 #include <asm/kprobes.h>
  14 #include <asm/mmu.h>
  15 #include <asm/ptrace.h>
  16 #include <asm/sections.h>
  17 #include <asm/stacktrace.h>
  18 #include <asm/sysreg.h>
  19 #include <asm/vmap_stack.h>
  20
  21 unsigned long sdei_exit_mode;
  22
  23 /*
  24  * VMAP'd stacks checking for stack overflow on exception using sp as a scratch
  25  * register, meaning SDEI has to switch to its own stack. We need two stacks as
  26  * a critical event may interrupt a normal event that has just taken a
  27  * synchronous exception, and is using sp as scratch register. For a critical
  28  * event interrupting a normal event, we can't reliably tell if we were on the
  29  * sdei stack.
  30  * For now, we allocate stacks when the driver is probed.
  31  */
  32 DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
  33 DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
  34
  35 #ifdef CONFIG_VMAP_STACK
  36 DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
  37 DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
  38 #endif
  39
  40 static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
  41 {
  42         unsigned long *p;
  43
  44         p = per_cpu(*ptr, cpu);
  45         if (p) {
  46                 per_cpu(*ptr, cpu) = NULL;
  47                 vfree(p);
  48         }
  49 }
  50
  51 static void free_sdei_stacks(void)
  52 {
  53         int cpu;
  54
  55         for_each_possible_cpu(cpu) {
  56                 _free_sdei_stack(&sdei_stack_normal_ptr, cpu);
  57                 _free_sdei_stack(&sdei_stack_critical_ptr, cpu);
  58         }
  59 }
  60
  61 static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
  62 {
  63         unsigned long *p;
  64
  65         p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
  66         if (!p)
  67                 return -ENOMEM;
  68         per_cpu(*ptr, cpu) = p;
  69
  70         return 0;
  71 }
  72
  73 static int init_sdei_stacks(void)
  74 {
  75         int cpu;
  76         int err = 0;
  77
  78         for_each_possible_cpu(cpu) {
  79                 err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
  80                 if (err)
  81                         break;
  82                 err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
  83                 if (err)
  84                         break;
  85         }
  86
  87         if (err)
  88                 free_sdei_stacks();
  89
  90         return err;
  91 }
  92
  93 static bool on_sdei_normal_stack(unsigned long sp, struct stack_info *info)
  94 {
  95         unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_normal_ptr);
  96         unsigned long high = low + SDEI_STACK_SIZE;
  97
  98         if (!low)
  99                 return false;
 100
 101         if (sp < low || sp >= high)
 102                 return false;
 103
 104         if (info) {
 105                 info->low = low;
 106                 info->high = high;
 107                 info->type = STACK_TYPE_SDEI_NORMAL;
 108         }
 109
 110         return true;
 111 }
 112
 113 static bool on_sdei_critical_stack(unsigned long sp, struct stack_info *info)
 114 {
 115         unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_critical_ptr);
 116         unsigned long high = low + SDEI_STACK_SIZE;
 117
 118         if (!low)
 119                 return false;
 120
 121         if (sp < low || sp >= high)
 122                 return false;
 123
 124         if (info) {
 125                 info->low = low;
 126                 info->high = high;
 127                 info->type = STACK_TYPE_SDEI_CRITICAL;
 128         }
 129
 130         return true;
 131 }
 132
 133 bool _on_sdei_stack(unsigned long sp, struct stack_info *info)
 134 {
 135         if (!IS_ENABLED(CONFIG_VMAP_STACK))
 136                 return false;
 137
 138         if (on_sdei_critical_stack(sp, info))
 139                 return true;
 140
 141         if (on_sdei_normal_stack(sp, info))
 142                 return true;
 143
 144         return false;
 145 }
 146
 147 unsigned long sdei_arch_get_entry_point(int conduit)
 148 {
 149         /*
 150          * SDEI works between adjacent exception levels. If we booted at EL1 we
 151          * assume a hypervisor is marshalling events. If we booted at EL2 and
 152          * dropped to EL1 because we don't support VHE, then we can't support
 153          * SDEI.
 154          */
 155         if (is_hyp_mode_available() && !is_kernel_in_hyp_mode()) {
 156                 pr_err("Not supported on this hardware/boot configuration\n");
 157                 return 0;
 158         }
 159
 160         if (IS_ENABLED(CONFIG_VMAP_STACK)) {
 161                 if (init_sdei_stacks())
 162                         return 0;
 163         }
 164
 165         sdei_exit_mode = (conduit == SMCCC_CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
 166
 167 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 168         if (arm64_kernel_unmapped_at_el0()) {
 169                 unsigned long offset;
 170
 171                 offset = (unsigned long)__sdei_asm_entry_trampoline -
 172                          (unsigned long)__entry_tramp_text_start;
 173                 return TRAMP_VALIAS + offset;
 174         } else
 175 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 176                 return (unsigned long)__sdei_asm_handler;
 177
 178 }
 179
 180 /*
 181  * __sdei_handler() returns one of:
 182  *  SDEI_EV_HANDLED -  success, return to the interrupted context.
 183  *  SDEI_EV_FAILED  -  failure, return this error code to firmare.
 184  *  virtual-address -  success, return to this address.
 185  */
 186 static __kprobes unsigned long _sdei_handler(struct pt_regs *regs,
 187                                              struct sdei_registered_event *arg)
 188 {
 189         u32 mode;
 190         int i, err = 0;
 191         int clobbered_registers = 4;
 192         u64 elr = read_sysreg(elr_el1);
 193         u32 kernel_mode = read_sysreg(CurrentEL) | 1;   /* +SPSel */
 194         unsigned long vbar = read_sysreg(vbar_el1);
 195
 196         if (arm64_kernel_unmapped_at_el0())
 197                 clobbered_registers++;
 198
 199         /* Retrieve the missing registers values */
 200         for (i = 0; i < clobbered_registers; i++) {
 201                 /* from within the handler, this call always succeeds */
 202                 sdei_api_event_context(i, &regs->regs[i]);
 203         }
 204
 205         /*
 206          * We didn't take an exception to get here, set PAN. UAO will be cleared
 207          * by sdei_event_handler()s set_fs(USER_DS) call.
 208          */
 209         __uaccess_enable_hw_pan();
 210
 211         err = sdei_event_handler(regs, arg);
 212         if (err)
 213                 return SDEI_EV_FAILED;
 214
 215         if (elr != read_sysreg(elr_el1)) {
 216                 /*
 217                  * We took a synchronous exception from the SDEI handler.
 218                  * This could deadlock, and if you interrupt KVM it will
 219                  * hyp-panic instead.
 220                  */
 221                 pr_warn("unsafe: exception during handler\n");
 222         }
 223
 224         mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);
 225
 226         /*
 227          * If we interrupted the kernel with interrupts masked, we always go
 228          * back to wherever we came from.
 229          */
 230         if (mode == kernel_mode && !interrupts_enabled(regs))
 231                 return SDEI_EV_HANDLED;
 232
 233         /*
 234          * Otherwise, we pretend this was an IRQ. This lets user space tasks
 235          * receive signals before we return to them, and KVM to invoke it's
 236          * world switch to do the same.
 237          *
 238          * See DDI0487B.a Table D1-7 'Vector offsets from vector table base
 239          * address'.
 240          */
 241         if (mode == kernel_mode)
 242                 return vbar + 0x280;
 243         else if (mode & PSR_MODE32_BIT)
 244                 return vbar + 0x680;
 245
 246         return vbar + 0x480;
 247 }
 248
 249
 250 asmlinkage __kprobes notrace unsigned long
 251 __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
 252 {
 253         unsigned long ret;
 254         bool do_nmi_exit = false;
 255
 256         /*
 257          * nmi_enter() deals with printk() re-entrance and use of RCU when
 258          * RCU believed this CPU was idle. Because critical events can
 259          * interrupt normal events, we may already be in_nmi().
 260          */
 261         if (!in_nmi()) {
 262                 nmi_enter();
 263                 do_nmi_exit = true;
 264         }
 265
 266         ret = _sdei_handler(regs, arg);
 267
 268         if (do_nmi_exit)
 269                 nmi_exit();
 270
 271         return ret;
 272 }