arm64: Add support for function error injection

Inspired by the commit 7cd01b0 ("powerpc: Add support for function
error injection"), this patch supports function error injection for
Arm64.

This patch mainly support two functions: one is regs_set_return_value()
which is used to overwrite the return value; the another function is
override_function_with_return() which is to override the probed
function returning and jump to its caller.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/Kconfig

@@ -148,6 +148,7 @@ config ARM64
 	select HAVE_FAST_GUP
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_TRACER
+	select HAVE_FUNCTION_ERROR_INJECTION
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_GCC_PLUGINS
 	select HAVE_HW_BREAKPOINT if PERF_EVENTS

arch/arm64/include/asm/ptrace.h

@@ -301,6 +301,11 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
 	return regs->regs[0];
 }
 
+static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
+{
+	regs->regs[0] = rc;
+}
+
 /**
  * regs_get_kernel_argument() - get Nth function argument in kernel
  * @regs:	pt_regs of that context

arch/arm64/lib/Makefile

@@ -33,3 +33,5 @@ UBSAN_SANITIZE_atomic_ll_sc.o	:= n
 lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o
 
 obj-$(CONFIG_CRC32) += crc32.o
+
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o

arch/arm64/lib/error-inject.c

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/error-injection.h>
+#include <linux/kprobes.h>
+
+void override_function_with_return(struct pt_regs *regs)
+{
+	/*
+	 * 'regs' represents the state on entry of a predefined function in
+	 * the kernel/module and which is captured on a kprobe.
+	 *
+	 * When kprobe returns back from exception it will override the end
+	 * of probed function and directly return to the predefined
+	 * function's caller.
+	 */
+	instruction_pointer_set(regs, procedure_link_pointer(regs));
+}
+NOKPROBE_SYMBOL(override_function_with_return);