1 files changed, 164 insertions, 0 deletions
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
new file mode 100644
index 000000000..9a70d9746
--- /dev/null
+++ b/arch/arm64/kernel/syscall.c
@@ -0,0 +1,164 @@
+// 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>
+
+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)
+{
+#ifdef CONFIG_COMPAT
+	long ret;
+	if (is_compat_task()) {
+		ret = compat_arm_syscall(regs, scno);
+		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);
+}
+
+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 (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);
+
+	/*
+	 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
+	 * but not enough for arm64 stack utilization comfort. To keep
+	 * reasonable stack head room, reduce the maximum offset to 9 bits.
+	 *
+	 * The actual entropy will be further reduced by the compiler when
+	 * applying stack alignment constraints: the AAPCS mandates a
+	 * 16-byte (i.e. 4-bit) aligned SP at function boundaries.
+	 *
+	 * The resulting 5 bits of entropy is seen in SP[8:4].
+	 */
+	choose_random_kstack_offset(get_random_u16() & 0x1FF);
+}
+
+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 (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_compat_syscalls,
+		       compat_sys_call_table);
+}
+#endif