powerpc: Add support for function error injection

We implement regs_set_return_value() and override_function_with_return()
for this purpose.

On powerpc, a return from a function (blr) just branches to the location
contained in the link register. So, we can just update pt_regs rather
than redirecting execution to a dummy function that returns.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

5 files changed, 37 insertions, 0 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 3d008115fe18..076e05ae9b04 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -190,6 +190,7 @@ config PPC
         select HAVE_EBPF_JIT                    if PPC64
         select HAVE_EFFICIENT_UNALIGNED_ACCESS  if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
         select HAVE_FTRACE_MCOUNT_RECORD
+        select HAVE_FUNCTION_ERROR_INJECTION
         select HAVE_FUNCTION_GRAPH_TRACER
         select HAVE_FUNCTION_TRACER
         select HAVE_GCC_PLUGINS                 if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC
diff --git a/arch/powerpc/include/asm/error-injection.h b/arch/powerpc/include/asm/error-injection.h
new file mode 100644
index 000000000000..62fd24739852
--- /dev/null
+++ b/arch/powerpc/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/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index 2ba2a1e52291..33196b311964 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -133,6 +133,11 @@ static inline long regs_return_value(struct pt_regs *regs)
                 return -regs->gpr[3];
 }
 
+static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
+{
+        regs->gpr[3] = rc;
+}
+
 #ifdef __powerpc64__
 #define user_mode(regs) ((((regs)->msr) >> MSR_PR_LG) & 0x1)
 #else
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 703afa1808ed..3bf9fc6fd36c 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -12,6 +12,8 @@ obj-y += string.o alloc.o code-patching.o feature-fixups.o
 
 obj-$(CONFIG_PPC32)     += div64.o copy_32.o crtsavres.o strlen_32.o
 
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION)  += error-inject.o
+
 # See corresponding test in arch/powerpc/Makefile
 # 64-bit linker creates .sfpr on demand for final link (vmlinux),
 # so it is only needed for modules, and only for older linkers which
diff --git a/arch/powerpc/lib/error-inject.c b/arch/powerpc/lib/error-inject.c
new file mode 100644
index 000000000000..407b992fb02f
--- /dev/null
+++ b/arch/powerpc/lib/error-inject.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/error-injection.h>
+#include <linux/kprobes.h>
+#include <linux/uaccess.h>
+
+void override_function_with_return(struct pt_regs *regs)
+{
+        /*
+         * Emulate 'blr'. 'regs' represents the state on entry of a predefined
+         * function in the kernel/module, captured on a kprobe. We don't need
+         * to worry about 32-bit userspace on a 64-bit kernel.
+         */
+        regs->nip = regs->link;
+}
+NOKPROBE_SYMBOL(override_function_with_return);