This patch implements arm specific functions regs_set_return_value() and
override_function_with_return() to support function error injection.
In the exception flow, it updates pt_regs::ARM_pc with pt_regs::ARM_lr
so can override the probed function return.
Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/ptrace.h | 5 +++++
arch/arm/lib/Makefile | 2 ++
arch/arm/lib/error-inject.c | 19 +++++++++++++++++++
4 files changed, 27 insertions(+)
create mode 100644 arch/arm/lib/error-inject.c
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 33b00579beff..2d3d44a037f6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -77,6 +77,7 @@ config ARM
select HAVE_EXIT_THREAD
select HAVE_FAST_GUP if ARM_LPAE
select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
+ select HAVE_FUNCTION_ERROR_INJECTION if !THUMB2_KERNEL
select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
select HAVE_FUNCTION_TRACER if !XIP_KERNEL
select HAVE_GCC_PLUGINS
diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 91d6b7856be4..3b41f37b361a 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -89,6 +89,11 @@ static inline long regs_return_value(struct pt_regs *regs)
return regs->ARM_r0;
}
+static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
+{
+ regs->ARM_r0 = rc;
+}
+
#define instruction_pointer(regs) (regs)->ARM_pc
#ifdef CONFIG_THUMB2_KERNEL
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index b25c54585048..8f56484a7156 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -42,3 +42,5 @@ ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
CFLAGS_xor-neon.o += $(NEON_FLAGS)
obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o
endif
+
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
diff --git a/arch/arm/lib/error-inject.c b/arch/arm/lib/error-inject.c
new file mode 100644
index 000000000000..2d696dc94893
--- /dev/null
+++ b/arch/arm/lib/error-inject.c
@@ -0,0 +1,19 @@
+// 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.
+ *
+ * 'regs->ARM_lr' contains the the link register for the probed
+ * function, 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, regs->ARM_lr);
+}
+NOKPROBE_SYMBOL(override_function_with_return);
--
2.17.1
