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);
57 syscall_set_return_value(current, regs, 0, ret);
60 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
61 * but not enough for arm64 stack utilization comfort. To keep
62 * reasonable stack head room, reduce the maximum offset to 9 bits.
64 * The actual entropy will be further reduced by the compiler when
65 * applying stack alignment constraints: the AAPCS mandates a
66 * 16-byte (i.e. 4-bit) aligned SP at function boundaries.
68 * The resulting 5 bits of entropy is seen in SP[8:4].
70 choose_random_kstack_offset(get_random_u16() & 0x1FF);
73 static inline bool has_syscall_work(unsigned long flags)
75 return unlikely(flags & _TIF_SYSCALL_WORK);
78 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
79 const syscall_fn_t syscall_table[])
81 unsigned long flags = read_thread_flags();
83 regs->orig_x0 = regs->regs[0];
84 regs->syscallno = scno;
88 * The architecture does not guarantee that SPSR.BTYPE is zero
89 * on taking an SVC, so we could return to userspace with a
90 * non-zero BTYPE after the syscall.
92 * This shouldn't matter except when userspace is explicitly
93 * doing something stupid, such as setting PROT_BTI on a page
94 * that lacks conforming BTI/PACIxSP instructions, falling
95 * through from one executable page to another with differing
96 * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
97 * userspace should not be surprised if a SIGILL occurs on
100 * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
101 * (Similarly for HVC and SMC elsewhere.)
104 local_daif_restore(DAIF_PROCCTX);
106 if (flags & _TIF_MTE_ASYNC_FAULT) {
108 * Process the asynchronous tag check fault before the actual
109 * syscall. do_notify_resume() will send a signal to userspace
110 * before the syscall is restarted.
112 syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
116 if (has_syscall_work(flags)) {
118 * The de-facto standard way to skip a system call using ptrace
119 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
120 * suitable error code for consumption by userspace. However,
121 * this cannot be distinguished from a user-issued syscall(-1)
122 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
123 * issue the skip and we fall into trace_exit with x0 preserved.
125 * This is slightly odd because it also means that if a tracer
126 * sets the system call number to -1 but does not initialise x0,
127 * then x0 will be preserved for all system calls apart from a
128 * user-issued syscall(-1). However, requesting a skip and not
129 * setting the return value is unlikely to do anything sensible
132 if (scno == NO_SYSCALL)
133 syscall_set_return_value(current, regs, -ENOSYS, 0);
134 scno = syscall_trace_enter(regs);
135 if (scno == NO_SYSCALL)
139 invoke_syscall(regs, scno, sc_nr, syscall_table);
142 * The tracing status may have changed under our feet, so we have to
143 * check again. However, if we were tracing entry, then we always trace
144 * exit regardless, as the old entry assembly did.
146 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
147 flags = read_thread_flags();
148 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
153 syscall_trace_exit(regs);
157 * As per the ABI exit SME streaming mode and clear the SVE state not
158 * shared with FPSIMD on syscall entry.
160 static inline void fp_user_discard(void)
163 * If SME is active then exit streaming mode. If ZA is active
164 * then flush the SVE registers but leave userspace access to
165 * both SVE and SME enabled, otherwise disable SME for the
166 * task and fall through to disabling SVE too. This means
167 * that after a syscall we never have any streaming mode
168 * register state to track, if this changes the KVM code will
171 if (system_supports_sme())
174 if (!system_supports_sve())
177 if (test_thread_flag(TIF_SVE)) {
178 unsigned int sve_vq_minus_one;
180 sve_vq_minus_one = sve_vq_from_vl(task_get_sve_vl(current)) - 1;
181 sve_flush_live(true, sve_vq_minus_one);
185 void do_el0_svc(struct pt_regs *regs)
188 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
192 void do_el0_svc_compat(struct pt_regs *regs)
194 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
195 compat_sys_call_table);