1 // SPDX-License-Identifier: GPL-2.0
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/randomize_kstack.h>
9 #include <linux/syscalls.h>
11 #include <asm/daifflags.h>
12 #include <asm/debug-monitors.h>
13 #include <asm/exception.h>
14 #include <asm/fpsimd.h>
15 #include <asm/syscall.h>
16 #include <asm/thread_info.h>
17 #include <asm/unistd.h>
19 long compat_arm_syscall(struct pt_regs *regs, int scno);
20 long sys_ni_syscall(void);
22 static long do_ni_syscall(struct pt_regs *regs, int scno)
26 if (is_compat_task()) {
27 ret = compat_arm_syscall(regs, scno);
33 return sys_ni_syscall();
36 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
38 return syscall_fn(regs);
41 static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
43 const syscall_fn_t syscall_table[])
47 add_random_kstack_offset();
50 syscall_fn_t syscall_fn;
51 syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
52 ret = __invoke_syscall(regs, syscall_fn);
54 ret = do_ni_syscall(regs, scno);
58 ret = lower_32_bits(ret);
63 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
64 * but not enough for arm64 stack utilization comfort. To keep
65 * reasonable stack head room, reduce the maximum offset to 9 bits.
67 * The actual entropy will be further reduced by the compiler when
68 * applying stack alignment constraints: the AAPCS mandates a
69 * 16-byte (i.e. 4-bit) aligned SP at function boundaries.
71 * The resulting 5 bits of entropy is seen in SP[8:4].
73 choose_random_kstack_offset(get_random_int() & 0x1FF);
76 static inline bool has_syscall_work(unsigned long flags)
78 return unlikely(flags & _TIF_SYSCALL_WORK);
81 int syscall_trace_enter(struct pt_regs *regs);
82 void syscall_trace_exit(struct pt_regs *regs);
84 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
85 const syscall_fn_t syscall_table[])
87 unsigned long flags = current_thread_info()->flags;
89 regs->orig_x0 = regs->regs[0];
90 regs->syscallno = scno;
94 * The architecture does not guarantee that SPSR.BTYPE is zero
95 * on taking an SVC, so we could return to userspace with a
96 * non-zero BTYPE after the syscall.
98 * This shouldn't matter except when userspace is explicitly
99 * doing something stupid, such as setting PROT_BTI on a page
100 * that lacks conforming BTI/PACIxSP instructions, falling
101 * through from one executable page to another with differing
102 * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
103 * userspace should not be surprised if a SIGILL occurs on
106 * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
107 * (Similarly for HVC and SMC elsewhere.)
110 local_daif_restore(DAIF_PROCCTX);
112 if (flags & _TIF_MTE_ASYNC_FAULT) {
114 * Process the asynchronous tag check fault before the actual
115 * syscall. do_notify_resume() will send a signal to userspace
116 * before the syscall is restarted.
118 regs->regs[0] = -ERESTARTNOINTR;
122 if (has_syscall_work(flags)) {
124 * The de-facto standard way to skip a system call using ptrace
125 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
126 * suitable error code for consumption by userspace. However,
127 * this cannot be distinguished from a user-issued syscall(-1)
128 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
129 * issue the skip and we fall into trace_exit with x0 preserved.
131 * This is slightly odd because it also means that if a tracer
132 * sets the system call number to -1 but does not initialise x0,
133 * then x0 will be preserved for all system calls apart from a
134 * user-issued syscall(-1). However, requesting a skip and not
135 * setting the return value is unlikely to do anything sensible
138 if (scno == NO_SYSCALL)
139 regs->regs[0] = -ENOSYS;
140 scno = syscall_trace_enter(regs);
141 if (scno == NO_SYSCALL)
145 invoke_syscall(regs, scno, sc_nr, syscall_table);
148 * The tracing status may have changed under our feet, so we have to
149 * check again. However, if we were tracing entry, then we always trace
150 * exit regardless, as the old entry assembly did.
152 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
154 flags = current_thread_info()->flags;
155 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
157 local_daif_restore(DAIF_PROCCTX);
161 syscall_trace_exit(regs);
164 static inline void sve_user_discard(void)
166 if (!system_supports_sve())
169 clear_thread_flag(TIF_SVE);
172 * task_fpsimd_load() won't be called to update CPACR_EL1 in
173 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
174 * happens if a context switch or kernel_neon_begin() or context
175 * modification (sigreturn, ptrace) intervenes.
176 * So, ensure that CPACR_EL1 is already correct for the fast-path case.
181 void do_el0_svc(struct pt_regs *regs)
184 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
188 void do_el0_svc_compat(struct pt_regs *regs)
190 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
191 compat_sys_call_table);