arm64 fix for v7.0

- Implement a basic static call trampoline to fix CFI failures with the
   generic implementation.
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Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 fix from Will Deacon:

 - Implement a basic static call trampoline to fix CFI failures with the
   generic implementation

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64: Use static call trampolines when kCFI is enabled

arch/arm64/Kconfig

@@ -252,6 +252,7 @@ config ARM64
 	select HAVE_RSEQ
 	select HAVE_RUST if RUSTC_SUPPORTS_ARM64
 	select HAVE_STACKPROTECTOR
+	select HAVE_STATIC_CALL if CFI
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES

arch/arm64/include/asm/static_call.h

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_STATIC_CALL_H
+#define _ASM_STATIC_CALL_H
+
+#define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, target)		    \
+	asm("	.pushsection .static_call.text, \"ax\"		\n" \
+	    "	.align	4					\n" \
+	    "	.globl	" name "				\n" \
+	    name ":						\n" \
+	    "	hint	34	/* BTI C */			\n" \
+	    "	adrp	x16, 1f					\n" \
+	    "	ldr	x16, [x16, :lo12:1f]			\n" \
+	    "	br	x16					\n" \
+	    "	.type	" name ", %function			\n" \
+	    "	.size	" name ", . - " name "			\n" \
+	    "	.popsection					\n" \
+	    "	.pushsection .rodata, \"a\"			\n" \
+	    "	.align	3					\n" \
+	    "1:	.quad	" target "				\n" \
+	    "	.popsection					\n")
+
+#define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func)			\
+	__ARCH_DEFINE_STATIC_CALL_TRAMP(STATIC_CALL_TRAMP_STR(name), #func)
+
+#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\
+	ARCH_DEFINE_STATIC_CALL_TRAMP(name, __static_call_return0)
+
+#define ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name)			\
+	ARCH_DEFINE_STATIC_CALL_TRAMP(name, __static_call_return0)
+
+#endif /* _ASM_STATIC_CALL_H */

arch/arm64/kernel/Makefile

@@ -46,6 +46,7 @@ obj-$(CONFIG_MODULES)			+= module.o module-plts.o
 obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o perf_callchain.o
 obj-$(CONFIG_HARDLOCKUP_DETECTOR_PERF)	+= watchdog_hld.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
+obj-$(CONFIG_HAVE_STATIC_CALL)		+= static_call.o
 obj-$(CONFIG_CPU_PM)			+= sleep.o suspend.o
 obj-$(CONFIG_KGDB)			+= kgdb.o
 obj-$(CONFIG_EFI)			+= efi.o efi-rt-wrapper.o

arch/arm64/kernel/static_call.c

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/static_call.h>
+#include <linux/memory.h>
+#include <asm/text-patching.h>
+
+void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
+{
+	u64 literal;
+	int ret;
+
+	if (!func)
+		func = __static_call_return0;
+
+	/* decode the instructions to discover the literal address */
+	literal = ALIGN_DOWN((u64)tramp + 4, SZ_4K) +
+		  aarch64_insn_adrp_get_offset(le32_to_cpup(tramp + 4)) +
+		  8 * aarch64_insn_decode_immediate(AARCH64_INSN_IMM_12,
+						    le32_to_cpup(tramp + 8));
+
+	ret = aarch64_insn_write_literal_u64((void *)literal, (u64)func);
+	WARN_ON_ONCE(ret);
+}
+EXPORT_SYMBOL_GPL(arch_static_call_transform);

arch/arm64/kernel/vmlinux.lds.S

@@ -191,6 +191,7 @@ SECTIONS
 			LOCK_TEXT
 			KPROBES_TEXT
 			HYPERVISOR_TEXT
+			STATIC_CALL_TEXT
 			*(.gnu.warning)
 	}