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
 17long compat_arm_syscall(struct pt_regs *regs, int scno);
 18long sys_ni_syscall(void);
 19
 20static 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
 34static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
 35{
 36	return syscall_fn(regs);
 37}
 38
 39static 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	if (is_compat_task())
 54		ret = lower_32_bits(ret);
 55
 56	regs->regs[0] = ret;
 57}
 58
 59static inline bool has_syscall_work(unsigned long flags)
 60{
 61	return unlikely(flags & _TIF_SYSCALL_WORK);
 62}
 63
 64int syscall_trace_enter(struct pt_regs *regs);
 65void syscall_trace_exit(struct pt_regs *regs);
 66
 67#ifdef CONFIG_ARM64_ERRATUM_1463225
 68DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa);
 69
 70static void cortex_a76_erratum_1463225_svc_handler(void)
 71{
 72	u32 reg, val;
 73
 74	if (!unlikely(test_thread_flag(TIF_SINGLESTEP)))
 75		return;
 76
 77	if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225)))
 78		return;
 79
 80	__this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1);
 81	reg = read_sysreg(mdscr_el1);
 82	val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE;
 83	write_sysreg(val, mdscr_el1);
 84	asm volatile("msr daifclr, #8");
 85	isb();
 86
 87	/* We will have taken a single-step exception by this point */
 88
 89	write_sysreg(reg, mdscr_el1);
 90	__this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0);
 91}
 92#else
 93static void cortex_a76_erratum_1463225_svc_handler(void) { }
 94#endif /* CONFIG_ARM64_ERRATUM_1463225 */
 95
 96static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 97			   const syscall_fn_t syscall_table[])
 98{
 99	unsigned long flags = current_thread_info()->flags;
100
101	regs->orig_x0 = regs->regs[0];
102	regs->syscallno = scno;
103
104	/*
105	 * BTI note:
106	 * The architecture does not guarantee that SPSR.BTYPE is zero
107	 * on taking an SVC, so we could return to userspace with a
108	 * non-zero BTYPE after the syscall.
109	 *
110	 * This shouldn't matter except when userspace is explicitly
111	 * doing something stupid, such as setting PROT_BTI on a page
112	 * that lacks conforming BTI/PACIxSP instructions, falling
113	 * through from one executable page to another with differing
114	 * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
115	 * userspace should not be surprised if a SIGILL occurs on
116	 * syscall return.
117	 *
118	 * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
119	 * (Similarly for HVC and SMC elsewhere.)
120	 */
121
122	cortex_a76_erratum_1463225_svc_handler();
123	local_daif_restore(DAIF_PROCCTX);
124	user_exit();
125
126	if (has_syscall_work(flags)) {
127		/*
128		 * The de-facto standard way to skip a system call using ptrace
129		 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
130		 * suitable error code for consumption by userspace. However,
131		 * this cannot be distinguished from a user-issued syscall(-1)
132		 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
133		 * issue the skip and we fall into trace_exit with x0 preserved.
134		 *
135		 * This is slightly odd because it also means that if a tracer
136		 * sets the system call number to -1 but does not initialise x0,
137		 * then x0 will be preserved for all system calls apart from a
138		 * user-issued syscall(-1). However, requesting a skip and not
139		 * setting the return value is unlikely to do anything sensible
140		 * anyway.
141		 */
142		if (scno == NO_SYSCALL)
143			regs->regs[0] = -ENOSYS;
144		scno = syscall_trace_enter(regs);
145		if (scno == NO_SYSCALL)
146			goto trace_exit;
147	}
148
149	invoke_syscall(regs, scno, sc_nr, syscall_table);
150
151	/*
152	 * The tracing status may have changed under our feet, so we have to
153	 * check again. However, if we were tracing entry, then we always trace
154	 * exit regardless, as the old entry assembly did.
155	 */
156	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
157		local_daif_mask();
158		flags = current_thread_info()->flags;
159		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) {
160			/*
161			 * We're off to userspace, where interrupts are
162			 * always enabled after we restore the flags from
163			 * the SPSR.
164			 */
165			trace_hardirqs_on();
166			return;
167		}
168		local_daif_restore(DAIF_PROCCTX);
169	}
170
171trace_exit:
172	syscall_trace_exit(regs);
173}
174
175static inline void sve_user_discard(void)
176{
177	if (!system_supports_sve())
178		return;
179
180	clear_thread_flag(TIF_SVE);
181
182	/*
183	 * task_fpsimd_load() won't be called to update CPACR_EL1 in
184	 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
185	 * happens if a context switch or kernel_neon_begin() or context
186	 * modification (sigreturn, ptrace) intervenes.
187	 * So, ensure that CPACR_EL1 is already correct for the fast-path case.
188	 */
189	sve_user_disable();
190}
191
192void do_el0_svc(struct pt_regs *regs)
193{
194	sve_user_discard();
195	el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
196}
197
198#ifdef CONFIG_COMPAT
199void do_el0_svc_compat(struct pt_regs *regs)
200{
201	el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
202		       compat_sys_call_table);
203}
204#endif