// 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/randomize_kstack.h>
#include <linux/syscalls.h>

#include <asm/debug-monitors.h>
#include <asm/exception.h>
#include <asm/fpsimd.h>
#include <asm/syscall.h>
#include <asm/thread_info.h>
#include <asm/unistd.h>
#include <asm/unistd_compat_32.h>

long compat_arm_syscall(struct pt_regs *regs, int scno);
long sys_ni_syscall(void);

static long do_ni_syscall(struct pt_regs *regs, int scno)
{
        if (is_compat_task()) {
                long ret = compat_arm_syscall(regs, scno);
                if (ret != -ENOSYS)
                        return ret;
        }

        return sys_ni_syscall();
}

static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
{
        return syscall_fn(regs);
}

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

        add_random_kstack_offset();

        if (likely(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, scno);
        }

        syscall_set_return_value(current, regs, 0, ret);

        /*
         * This value will get limited by KSTACK_OFFSET_MAX(), which is 10
         * bits. The actual entropy will be further reduced by the compiler
         * when applying stack alignment constraints: the AAPCS mandates a
         * 16-byte aligned SP at function boundaries, which will remove the
         * 4 low bits from any entropy chosen here.
         *
         * The resulting 6 bits of entropy is seen in SP[9:4].
         */
        choose_random_kstack_offset(get_random_u16());
}

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

static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
                           const syscall_fn_t syscall_table[])
{
        unsigned long flags = read_thread_flags();

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

        /*
         * BTI note:
         * The architecture does not guarantee that SPSR.BTYPE is zero
         * on taking an SVC, so we could return to userspace with a
         * non-zero BTYPE after the syscall.
         *
         * This shouldn't matter except when userspace is explicitly
         * doing something stupid, such as setting PROT_BTI on a page
         * that lacks conforming BTI/PACIxSP instructions, falling
         * through from one executable page to another with differing
         * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
         * userspace should not be surprised if a SIGILL occurs on
         * syscall return.
         *
         * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
         * (Similarly for HVC and SMC elsewhere.)
         */

        if (unlikely(flags & _TIF_MTE_ASYNC_FAULT)) {
                /*
                 * Process the asynchronous tag check fault before the actual
                 * syscall. do_notify_resume() will send a signal to userspace
                 * before the syscall is restarted.
                 */
                syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
                return;
        }

        if (has_syscall_work(flags)) {
                /*
                 * The de-facto standard way to skip a system call using ptrace
                 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
                 * suitable error code for consumption by userspace. However,
                 * this cannot be distinguished from a user-issued syscall(-1)
                 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
                 * issue the skip and we fall into trace_exit with x0 preserved.
                 *
                 * This is slightly odd because it also means that if a tracer
                 * sets the system call number to -1 but does not initialise x0,
                 * then x0 will be preserved for all system calls apart from a
                 * user-issued syscall(-1). However, requesting a skip and not
                 * setting the return value is unlikely to do anything sensible
                 * anyway.
                 */
                if (scno == NO_SYSCALL)
                        syscall_set_return_value(current, regs, -ENOSYS, 0);
                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)) {
                flags = read_thread_flags();
                if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
                        return;
        }

trace_exit:
        syscall_trace_exit(regs);
}

void do_el0_svc(struct pt_regs *regs)
{
        el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
}

#ifdef CONFIG_COMPAT
void do_el0_svc_compat(struct pt_regs *regs)
{
        el0_svc_common(regs, regs->regs[7], __NR_compat32_syscalls,
                       compat_sys_call_table);
}
#endif