syscall.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/compiler.h>
#include <linux/context_tracking.h>
#include <linux/errno.h>
#include <linux/nospec.h>
#include <linux/ptrace.h>
#include <linux/syscalls.h>

#include <asm/daifflags.h>
#include <asm/syscall.h>
#include <asm/thread_info.h>

long compat_arm_syscall(struct pt_regs *regs);

asmlinkage long do_ni_syscall(struct pt_regs *regs)
{
#ifdef CONFIG_COMPAT
	long ret;
	if (is_compat_task()) {
		ret = compat_arm_syscall(regs);
		if (ret != -ENOSYS)
			return ret;
	}
#endif

	return sys_ni_syscall();
}

static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
{
	return syscall_fn(regs->regs[0], regs->regs[1], regs->regs[2],
			  regs->regs[3], regs->regs[4], regs->regs[5]);
}

static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
			   unsigned int sc_nr,
			   const syscall_fn_t syscall_table[])
{
	long ret;

	if (scno < sc_nr) {
		syscall_fn_t syscall_fn;
		syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
		ret = __invoke_syscall(regs, syscall_fn);
	} else {
		ret = do_ni_syscall(regs);
	}

	regs->regs[0] = ret;
}

static inline bool has_syscall_work(unsigned long flags)
{
	return unlikely(flags & _TIF_SYSCALL_WORK);
}

int syscall_trace_enter(struct pt_regs *regs);
void syscall_trace_exit(struct pt_regs *regs);

asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
			       const syscall_fn_t syscall_table[])
{
	unsigned long flags = current_thread_info()->flags;

	regs->orig_x0 = regs->regs[0];
	regs->syscallno = scno;

	local_daif_restore(DAIF_PROCCTX);
	user_exit();

	if (has_syscall_work(flags)) {
		/* set default errno for user-issued syscall(-1) */
		if (scno == NO_SYSCALL)
			regs->regs[0] = -ENOSYS;
		scno = syscall_trace_enter(regs);
		if (scno == NO_SYSCALL)
			goto trace_exit;
	}

	invoke_syscall(regs, scno, sc_nr, syscall_table);

	/*
	 * The tracing status may have changed under our feet, so we have to
	 * check again. However, if we were tracing entry, then we always trace
	 * exit regardless, as the old entry assembly did.
	 */
	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
		local_daif_mask();
		flags = current_thread_info()->flags;
		if (!has_syscall_work(flags))
			return;
		local_daif_restore(DAIF_PROCCTX);
	}

trace_exit:
	syscall_trace_exit(regs);
}