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Subject[PATCH 1/2] arm64: Add support for function error injection
Date
This patch implement regs_set_return_value() and
override_function_with_return() to support function error injection
for arm64.

In the exception flow, arm64's general register x30 contains the value
for the link register; so we can just update pt_regs::pc with it rather
than redirecting execution to a dummy function that returns.

This patch is heavily inspired by the commit 7cd01b08d35f ("powerpc:
Add support for function error injection").

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/error-injection.h | 13 +++++++++++++
arch/arm64/include/asm/ptrace.h | 5 +++++
arch/arm64/lib/Makefile | 2 ++
arch/arm64/lib/error-inject.c | 19 +++++++++++++++++++
5 files changed, 40 insertions(+)
create mode 100644 arch/arm64/include/asm/error-injection.h
create mode 100644 arch/arm64/lib/error-inject.c

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 697ea0510729..a6d9e622977d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -142,6 +142,7 @@ config ARM64
select HAVE_EFFICIENT_UNALIGNED_ACCESS
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
diff --git a/arch/arm64/include/asm/error-injection.h b/arch/arm64/include/asm/error-injection.h
new file mode 100644
index 000000000000..da057e8ed224
--- /dev/null
+++ b/arch/arm64/include/asm/error-injection.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#ifndef __ASM_ERROR_INJECTION_H_
+#define __ASM_ERROR_INJECTION_H_
+
+#include <linux/compiler.h>
+#include <linux/linkage.h>
+#include <asm/ptrace.h>
+#include <asm-generic/error-injection.h>
+
+void override_function_with_return(struct pt_regs *regs);
+
+#endif /* __ASM_ERROR_INJECTION_H_ */
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index dad858b6adc6..3aafbbe218a2 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -294,6 +294,11 @@ 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
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 33c2a4abda04..f182ccb0438e 100644
--- a/arch/arm64/lib/Makefile
+++ b/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
diff --git a/arch/arm64/lib/error-inject.c b/arch/arm64/lib/error-inject.c
new file mode 100644
index 000000000000..35661c2de4b0
--- /dev/null
+++ b/arch/arm64/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->regs[30]' contains the the link register for the probed
+ * function and assign it to 'regs->pc', so when kprobe returns
+ * back from exception it will override the end of probed function
+ * and drirectly return to the predefined function's caller.
+ */
+ regs->pc = regs->regs[30];
+}
+NOKPROBE_SYMBOL(override_function_with_return);
--
2.17.1
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