arch/arm64/kernel/syscall.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/compiler.h>
   4 #include <linux/context_tracking.h>
   5 #include <linux/errno.h>
   6 #include <linux/nospec.h>
   7 #include <linux/ptrace.h>
   8 #include <linux/syscalls.h>
   9
  10 #include <asm/daifflags.h>
  11 #include <asm/debug-monitors.h>
  12 #include <asm/fpsimd.h>
  13 #include <asm/syscall.h>
  14 #include <asm/thread_info.h>
  15 #include <asm/unistd.h>
  16
  17 long compat_arm_syscall(struct pt_regs *regs, int scno);
  18 long sys_ni_syscall(void);
  19
  20 static long do_ni_syscall(struct pt_regs *regs, int scno)
  21 {
  22 #ifdef CONFIG_COMPAT
  23         long ret;
  24         if (is_compat_task()) {
  25                 ret = compat_arm_syscall(regs, scno);
  26                 if (ret != -ENOSYS)
  27                         return ret;
  28         }
  29 #endif
  30
  31         return sys_ni_syscall();
  32 }
  33
  34 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
  35 {
  36         return syscall_fn(regs);
  37 }
  38
  39 static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
  40                            unsigned int sc_nr,
  41                            const syscall_fn_t syscall_table[])
  42 {
  43         long ret;
  44
  45         if (scno < sc_nr) {
  46                 syscall_fn_t syscall_fn;
  47                 syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
  48                 ret = __invoke_syscall(regs, syscall_fn);
  49         } else {
  50                 ret = do_ni_syscall(regs, scno);
  51         }
  52
  53         regs->regs[0] = ret;
  54 }
  55
  56 static inline bool has_syscall_work(unsigned long flags)
  57 {
  58         return unlikely(flags & _TIF_SYSCALL_WORK);
  59 }
  60
  61 int syscall_trace_enter(struct pt_regs *regs);
  62 void syscall_trace_exit(struct pt_regs *regs);
  63
  64 #ifdef CONFIG_ARM64_ERRATUM_1463225
  65 DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa);
  66
  67 static void cortex_a76_erratum_1463225_svc_handler(void)
  68 {
  69         u32 reg, val;
  70
  71         if (!unlikely(test_thread_flag(TIF_SINGLESTEP)))
  72                 return;
  73
  74         if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225)))
  75                 return;
  76
  77         __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1);
  78         reg = read_sysreg(mdscr_el1);
  79         val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE;
  80         write_sysreg(val, mdscr_el1);
  81         asm volatile("msr daifclr, #8");
  82         isb();
  83
  84         /* We will have taken a single-step exception by this point */
  85
  86         write_sysreg(reg, mdscr_el1);
  87         __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0);
  88 }
  89 #else
  90 static void cortex_a76_erratum_1463225_svc_handler(void) { }
  91 #endif /* CONFIG_ARM64_ERRATUM_1463225 */
  92
  93 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
  94                            const syscall_fn_t syscall_table[])
  95 {
  96         unsigned long flags = current_thread_info()->flags;
  97
  98         regs->orig_x0 = regs->regs[0];
  99         regs->syscallno = scno;
 100
 101         cortex_a76_erratum_1463225_svc_handler();
 102         local_daif_restore(DAIF_PROCCTX);
 103         user_exit();
 104
 105         if (has_syscall_work(flags)) {
 106                 /* set default errno for user-issued syscall(-1) */
 107                 if (scno == NO_SYSCALL)
 108                         regs->regs[0] = -ENOSYS;
 109                 scno = syscall_trace_enter(regs);
 110                 if (scno == NO_SYSCALL)
 111                         goto trace_exit;
 112         }
 113
 114         invoke_syscall(regs, scno, sc_nr, syscall_table);
 115
 116         /*
 117          * The tracing status may have changed under our feet, so we have to
 118          * check again. However, if we were tracing entry, then we always trace
 119          * exit regardless, as the old entry assembly did.
 120          */
 121         if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
 122                 local_daif_mask();
 123                 flags = current_thread_info()->flags;
 124                 if (!has_syscall_work(flags)) {
 125                         /*
 126                          * We're off to userspace, where interrupts are
 127                          * always enabled after we restore the flags from
 128                          * the SPSR.
 129                          */
 130                         trace_hardirqs_on();
 131                         return;
 132                 }
 133                 local_daif_restore(DAIF_PROCCTX);
 134         }
 135
 136 trace_exit:
 137         syscall_trace_exit(regs);
 138 }
 139
 140 static inline void sve_user_discard(void)
 141 {
 142         if (!system_supports_sve())
 143                 return;
 144
 145         clear_thread_flag(TIF_SVE);
 146
 147         /*
 148          * task_fpsimd_load() won't be called to update CPACR_EL1 in
 149          * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
 150          * happens if a context switch or kernel_neon_begin() or context
 151          * modification (sigreturn, ptrace) intervenes.
 152          * So, ensure that CPACR_EL1 is already correct for the fast-path case.
 153          */
 154         sve_user_disable();
 155 }
 156
 157 void el0_svc_handler(struct pt_regs *regs)
 158 {
 159         sve_user_discard();
 160         el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
 161 }
 162
 163 #ifdef CONFIG_COMPAT
 164 void el0_svc_compat_handler(struct pt_regs *regs)
 165 {
 166         el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
 167                        compat_sys_call_table);
 168 }
 169 #endif