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>

1 files changed, 16 insertions, 0 deletions

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);