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_int() & 0x1FF);
73 static inline bool has_syscall_work(unsigned long flags)
75 return unlikely(flags & _TIF_SYSCALL_WORK);
78 int syscall_trace_enter(struct pt_regs *regs);
79 void syscall_trace_exit(struct pt_regs *regs);
81 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
82 const syscall_fn_t syscall_table[])
84 unsigned long flags = read_thread_flags();
86 regs->orig_x0 = regs->regs[0];
87 regs->syscallno = scno;
91 * The architecture does not guarantee that SPSR.BTYPE is zero
92 * on taking an SVC, so we could return to userspace with a
93 * non-zero BTYPE after the syscall.
95 * This shouldn't matter except when userspace is explicitly
96 * doing something stupid, such as setting PROT_BTI on a page
97 * that lacks conforming BTI/PACIxSP instructions, falling
98 * through from one executable page to another with differing
99 * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
100 * userspace should not be surprised if a SIGILL occurs on
103 * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
104 * (Similarly for HVC and SMC elsewhere.)
107 local_daif_restore(DAIF_PROCCTX);
109 if (flags & _TIF_MTE_ASYNC_FAULT) {
111 * Process the asynchronous tag check fault before the actual
112 * syscall. do_notify_resume() will send a signal to userspace
113 * before the syscall is restarted.
115 syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
119 if (has_syscall_work(flags)) {
121 * The de-facto standard way to skip a system call using ptrace
122 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
123 * suitable error code for consumption by userspace. However,
124 * this cannot be distinguished from a user-issued syscall(-1)
125 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
126 * issue the skip and we fall into trace_exit with x0 preserved.
128 * This is slightly odd because it also means that if a tracer
129 * sets the system call number to -1 but does not initialise x0,
130 * then x0 will be preserved for all system calls apart from a
131 * user-issued syscall(-1). However, requesting a skip and not
132 * setting the return value is unlikely to do anything sensible
135 if (scno == NO_SYSCALL)
136 syscall_set_return_value(current, regs, -ENOSYS, 0);
137 scno = syscall_trace_enter(regs);
138 if (scno == NO_SYSCALL)
142 invoke_syscall(regs, scno, sc_nr, syscall_table);
145 * The tracing status may have changed under our feet, so we have to
146 * check again. However, if we were tracing entry, then we always trace
147 * exit regardless, as the old entry assembly did.
149 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
151 flags = read_thread_flags();
152 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
154 local_daif_restore(DAIF_PROCCTX);
158 syscall_trace_exit(regs);
162 * As per the ABI exit SME streaming mode and clear the SVE state not
163 * shared with FPSIMD on syscall entry.
165 static inline void fp_user_discard(void)
168 * If SME is active then exit streaming mode. If ZA is active
169 * then flush the SVE registers but leave userspace access to
170 * both SVE and SME enabled, otherwise disable SME for the
171 * task and fall through to disabling SVE too. This means
172 * that after a syscall we never have any streaming mode
173 * register state to track, if this changes the KVM code will
176 if (system_supports_sme() && test_thread_flag(TIF_SME)) {
177 u64 svcr = read_sysreg_s(SYS_SVCR);
179 if (svcr & SVCR_SM_MASK)
183 if (!system_supports_sve())
187 * If SME is not active then disable SVE, the registers will
188 * be cleared when userspace next attempts to access them and
189 * we do not need to track the SVE register state until then.
191 clear_thread_flag(TIF_SVE);
194 * task_fpsimd_load() won't be called to update CPACR_EL1 in
195 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
196 * happens if a context switch or kernel_neon_begin() or context
197 * modification (sigreturn, ptrace) intervenes.
198 * So, ensure that CPACR_EL1 is already correct for the fast-path case.
203 void do_el0_svc(struct pt_regs *regs)
206 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
210 void do_el0_svc_compat(struct pt_regs *regs)
212 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
213 compat_sys_call_table);