[PATCH 08/18] arm64: convert raw syscall invocation to C

[Mark Rutland <mark.rutland@xxxxxxx>]

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.

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@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
---
 arch/arm64/kernel/Makefile  |  3 ++-
 arch/arm64/kernel/entry.S   | 36 ++++++++++--------------------------
 arch/arm64/kernel/syscall.c | 29 +++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 27 deletions(-)
 create mode 100644 arch/arm64/kernel/syscall.c

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index bf825f38d206..c22e8ace5ea3 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -18,7 +18,8 @@ arm64-obj-y		:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   hyp-stub.o psci.o cpu_ops.o insn.o	\
 			   return_address.o cpuinfo.o cpu_errata.o		\
 			   cpufeature.o alternative.o cacheinfo.o		\
-			   smp.o smp_spin_table.o topology.o smccc-call.o
+			   smp.o smp_spin_table.o topology.o smccc-call.o	\
+			   syscall.o
 
 extra-$(CONFIG_EFI)			:= efi-entry.o
 
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 08ea3cbfb08f..d6e057500eaf 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -873,7 +873,6 @@ ENDPROC(el0_error)
  */
 ret_fast_syscall:
 	disable_daif
-	str	x0, [sp, #S_X0]			// returned x0
 	ldr	x1, [tsk, #TSK_TI_FLAGS]	// re-check for syscall tracing
 	and	x2, x1, #_TIF_SYSCALL_WORK
 	cbnz	x2, ret_fast_syscall_trace
@@ -946,15 +945,11 @@ el0_svc_naked:					// compat entry point
 
 	tst	x16, #_TIF_SYSCALL_WORK		// check for syscall hooks
 	b.ne	__sys_trace
-	cmp     wscno, wsc_nr			// check upper syscall limit
-	b.hs	ni_sys
-	mask_nospec64 xscno, xsc_nr, x19	// enforce bounds for syscall number
-	ldr	x16, [stbl, xscno, lsl #3]	// address in the syscall table
-	blr	x16				// call sys_* routine
-	b	ret_fast_syscall
-ni_sys:
 	mov	x0, sp
-	bl	do_ni_syscall
+	mov	w1, wscno
+	mov	w2, wsc_nr
+	mov	x3, stbl
+	bl	invoke_syscall
 	b	ret_fast_syscall
 ENDPROC(el0_svc)
 
@@ -971,29 +966,18 @@ __sys_trace:
 	bl	syscall_trace_enter
 	cmp	w0, #NO_SYSCALL			// skip the syscall?
 	b.eq	__sys_trace_return_skipped
-	mov	wscno, w0			// syscall number (possibly new)
-	mov	x1, sp				// pointer to regs
-	cmp	wscno, wsc_nr			// check upper syscall limit
-	b.hs	__ni_sys_trace
-	ldp	x0, x1, [sp]			// restore the syscall args
-	ldp	x2, x3, [sp, #S_X2]
-	ldp	x4, x5, [sp, #S_X4]
-	ldp	x6, x7, [sp, #S_X6]
-	ldr	x16, [stbl, xscno, lsl #3]	// address in the syscall table
-	blr	x16				// call sys_* routine
 
-__sys_trace_return:
-	str	x0, [sp, #S_X0]			// save returned x0
+	mov	x0, sp
+	mov	w1, wscno
+	mov w2, wsc_nr
+	mov	x3, stbl
+	bl	invoke_syscall
+
 __sys_trace_return_skipped:
 	mov	x0, sp
 	bl	syscall_trace_exit
 	b	ret_to_user
 
-__ni_sys_trace:
-	mov	x0, sp
-	bl	do_ni_syscall
-	b	__sys_trace_return
-
 	.popsection				// .entry.text
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
new file mode 100644
index 000000000000..58d7569f47df
--- /dev/null
+++ b/arch/arm64/kernel/syscall.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/nospec.h>
+#include <linux/ptrace.h>
+
+long do_ni_syscall(struct pt_regs *regs);
+
+typedef long (*syscall_fn_t)(unsigned long, unsigned long,
+			     unsigned long, unsigned long,
+			     unsigned long, unsigned long);
+
+static void __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
+{
+	regs->regs[0] = 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, int scno, int sc_nr,
+			       syscall_fn_t syscall_table[])
+{
+	if (scno < sc_nr) {
+		syscall_fn_t syscall_fn;
+		syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
+		__invoke_syscall(regs, syscall_fn);
+	} else {
+		regs->regs[0] = do_ni_syscall(regs);
+	}
+}
-- 
2.11.0