arm64: convert raw syscall invocation to C

As a first step towards invoking syscalls with a pt_regs argument,
convert the raw syscall invocation logic to C. We end up with a bit more
register shuffling, but the unified invocation logic means we can unify
the tracing paths, too.

Previously, assembly had to open-code calls to ni_sys() when the system
call number was out-of-bounds for the relevant syscall table. This case
is now handled by invoke_syscall(), and the assembly no longer need to
handle this case explicitly. This allows the tracing paths to be
simplified and unified, as we no longer need the __ni_sys_trace path and
the __sys_trace_return label.

This only converts the invocation of the syscall. The rest of the
syscall triage and tracing is left in assembly for now, and will be
converted in subsequent patches.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 47 insertions, 0 deletions

diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
new file mode 100644
index 000000000000..93d36f22647e
--- /dev/null
+++ b/arch/arm64/kernel/syscall.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/errno.h>
+#include <linux/nospec.h>
+#include <linux/ptrace.h>
+#include <linux/syscalls.h>
+
+#include <asm/syscall.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]);
+}
+
+asmlinkage 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;
+}