[PATCH v12 bpf-next 06/12] powerpc: Add rethook support

[Masami Hiramatsu <mhiramat@kernel.org>]

Add rethook powerpc64 implementation. Most of the code has been copied from
kretprobes on powerpc64.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v10:
  - Add a dummy @mcount to arch_rethook_prepare().
---
 arch/powerpc/Kconfig          |    1 +
 arch/powerpc/kernel/Makefile  |    1 +
 arch/powerpc/kernel/rethook.c |   72 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 74 insertions(+)
 create mode 100644 arch/powerpc/kernel/rethook.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index b779603978e1..5feaa241fb56 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -229,6 +229,7 @@ config PPC
 	select HAVE_PERF_EVENTS_NMI		if PPC64
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_RETHOOK			if KPROBES
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RELIABLE_STACKTRACE
 	select HAVE_RSEQ
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 4d7829399570..feb24ea83ca6 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -115,6 +115,7 @@ obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
 obj-$(CONFIG_OPTPROBES)		+= optprobes.o optprobes_head.o
 obj-$(CONFIG_KPROBES_ON_FTRACE)	+= kprobes-ftrace.o
+obj-$(CONFIG_RETHOOK)		+= rethook.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o
 obj-$(CONFIG_PPC_UDBG_16550)	+= legacy_serial.o udbg_16550.o
 obj-$(CONFIG_SWIOTLB)		+= dma-swiotlb.o
diff --git a/arch/powerpc/kernel/rethook.c b/arch/powerpc/kernel/rethook.c
new file mode 100644
index 000000000000..a8a128748efa
--- /dev/null
+++ b/arch/powerpc/kernel/rethook.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * PowerPC implementation of rethook. This depends on kprobes.
+ */
+
+#include <linux/kprobes.h>
+#include <linux/rethook.h>
+
+/*
+ * Function return trampoline:
+ * 	- init_kprobes() establishes a probepoint here
+ * 	- When the probed function returns, this probe
+ * 		causes the handlers to fire
+ */
+asm(".global arch_rethook_trampoline\n"
+	".type arch_rethook_trampoline, @function\n"
+	"arch_rethook_trampoline:\n"
+	"nop\n"
+	"blr\n"
+	".size arch_rethook_trampoline, .-arch_rethook_trampoline\n");
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+static int trampoline_rethook_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	unsigned long orig_ret_address;
+
+	orig_ret_address = rethook_trampoline_handler(regs, 0);
+	/*
+	 * We get here through one of two paths:
+	 * 1. by taking a trap -> kprobe_handler() -> here
+	 * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
+	 *
+	 * When going back through (1), we need regs->nip to be setup properly
+	 * as it is used to determine the return address from the trap.
+	 * For (2), since nip is not honoured with optprobes, we instead setup
+	 * the link register properly so that the subsequent 'blr' in
+	 * __kretprobe_trampoline jumps back to the right instruction.
+	 *
+	 * For nip, we should set the address to the previous instruction since
+	 * we end up emulating it in kprobe_handler(), which increments the nip
+	 * again.
+	 */
+	regs_set_return_ip(regs, orig_ret_address - 4);
+	regs->link = orig_ret_address;
+
+	return 0;
+}
+NOKPROBE_SYMBOL(trampoline_rethook_handler);
+
+void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
+{
+	rh->ret_addr = regs->link;
+	rh->frame = 0;
+
+	/* Replace the return addr with trampoline addr */
+	regs->link = (unsigned long)arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_prepare_kretprobe);
+
+static struct kprobe trampoline_p = {
+	.addr = (kprobe_opcode_t *) &arch_rethook_trampoline,
+	.pre_handler = trampoline_rethook_handler
+};
+
+static int init_arch_rethook(void)
+{
+	return register_kprobe(&trampoline_p);
+}
+
+core_initcall(init_arch_rethook);