powerpc: Replace kretprobe code with rethook on powerpc

This is an adaptation of commit f3a112c0c4 ("x86,rethook,kprobes:
Replace kretprobe with rethook on x86") to powerpc.

Rethook follows the existing kretprobe implementation, but separates
it from kprobes so that it can be used by fprobe (ftrace-based
function entry/exit probes). As such, this patch also enables fprobe
to work on powerpc. The only other change compared to the existing
kretprobe implementation is doing the return address fixup in
arch_rethook_fixup_return().

Reference to other archs:
commit b57c2f1240 ("riscv: add riscv rethook implementation")
commit 7b0a096436 ("LoongArch: Replace kretprobe with rethook")

Note:
=====

In future, rethook will be only for kretprobe, and kretprobe
will be replaced by fprobe.

https://lore.kernel.org/all/172000134410.63468.13742222887213469474.stgit@devnote2/

We will	adapt the above	implementation for powerpc once its upstream.
Until then, we can have	this implementation of rethook to serve
current	kretprobe usecases.

Reviewed-by: Naveen Rao <naveen@kernel.org>
Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240830113131.7597-1-adubey@linux.ibm.com

arch/powerpc/Kconfig

@@ -269,6 +269,7 @@ 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

arch/powerpc/kernel/Makefile

@@ -139,6 +139,7 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o
 obj-$(CONFIG_OPTPROBES)		+= optprobes.o optprobes_head.o
 obj-$(CONFIG_KPROBES_ON_FTRACE)	+= kprobes-ftrace.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o
+obj-$(CONFIG_RETHOOK)           += rethook.o
 obj-$(CONFIG_PPC_UDBG_16550)	+= legacy_serial.o udbg_16550.o
 obj-$(CONFIG_SWIOTLB)		+= dma-swiotlb.o
 obj-$(CONFIG_ARCH_HAS_DMA_SET_MASK) += dma-mask.o

arch/powerpc/kernel/kprobes.c

@@ -228,16 +228,6 @@ static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs
 	kcb->kprobe_saved_msr = regs->msr;
 }
 
-void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
-{
-	ri->ret_addr = (kprobe_opcode_t *)regs->link;
-	ri->fp = NULL;
-
-	/* Replace the return addr with trampoline addr */
-	regs->link = (unsigned long)__kretprobe_trampoline;
-}
-NOKPROBE_SYMBOL(arch_prepare_kretprobe);
-
 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
 {
 	int ret;
@@ -394,49 +384,6 @@ no_kprobe:
 }
 NOKPROBE_SYMBOL(kprobe_handler);
 
-/*
- * Function return probe trampoline:
- * 	- init_kprobes() establishes a probepoint here
- * 	- When the probed function returns, this probe
- * 		causes the handlers to fire
- */
-asm(".global __kretprobe_trampoline\n"
-	".type __kretprobe_trampoline, @function\n"
-	"__kretprobe_trampoline:\n"
-	"nop\n"
-	"blr\n"
-	".size __kretprobe_trampoline, .-__kretprobe_trampoline\n");
-
-/*
- * Called when the probe at kretprobe trampoline is hit
- */
-static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
-{
-	unsigned long orig_ret_address;
-
-	orig_ret_address = __kretprobe_trampoline_handler(regs, NULL);
-	/*
-	 * 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_probe_handler);
-
 /*
  * Called after single-stepping.  p->addr is the address of the
  * instruction whose first byte has been replaced by the "breakpoint"
@@ -539,19 +486,9 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 }
 NOKPROBE_SYMBOL(kprobe_fault_handler);
 
-static struct kprobe trampoline_p = {
-	.addr = (kprobe_opcode_t *) &__kretprobe_trampoline,
-	.pre_handler = trampoline_probe_handler
-};
-
-int __init arch_init_kprobes(void)
-{
-	return register_kprobe(&trampoline_p);
-}
-
 int arch_trampoline_kprobe(struct kprobe *p)
 {
-	if (p->addr == (kprobe_opcode_t *)&__kretprobe_trampoline)
+	if (p->addr == (kprobe_opcode_t *)&arch_rethook_trampoline)
 		return 1;
 
 	return 0;

arch/powerpc/kernel/optprobes.c

@@ -56,7 +56,7 @@ static unsigned long can_optimize(struct kprobe *p)
 	 * has a 'nop' instruction, which can be emulated.
 	 * So further checks can be skipped.
 	 */
-	if (p->addr == (kprobe_opcode_t *)&__kretprobe_trampoline)
+	if (p->addr == (kprobe_opcode_t *)&arch_rethook_trampoline)
 		return addr + sizeof(kprobe_opcode_t);
 
 	/*

arch/powerpc/kernel/rethook.c

@@ -0,0 +1,73 @@
+// 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)
+{
+	return !rethook_trampoline_handler(regs, regs->gpr[1]);
+}
+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 = regs->gpr[1];
+
+	/* Replace the return addr with trampoline addr */
+	regs->link = (unsigned long)arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_rethook_prepare);
+
+/* This is called from rethook_trampoline_handler(). */
+void arch_rethook_fixup_return(struct pt_regs *regs, unsigned long orig_ret_address)
+{
+	/*
+	 * 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
+	 * arch_rethook_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;
+}
+NOKPROBE_SYMBOL(arch_rethook_fixup_return);
+
+static struct kprobe trampoline_p = {
+	.addr = (kprobe_opcode_t *) &arch_rethook_trampoline,
+	.pre_handler = trampoline_rethook_handler
+};
+
+/* rethook initializer */
+int __init arch_init_kprobes(void)
+{
+	return register_kprobe(&trampoline_p);
+}

arch/powerpc/kernel/stacktrace.c

@@ -21,6 +21,7 @@
 #include <asm/processor.h>
 #include <linux/ftrace.h>
 #include <asm/kprobes.h>
+#include <linux/rethook.h>
 
 #include <asm/paca.h>
 
@@ -133,12 +134,13 @@ int __no_sanitize_address arch_stack_walk_reliable(stack_trace_consume_fn consum
 		 * arch-dependent code, they are generic.
 		 */
 		ip = ftrace_graph_ret_addr(task, &graph_idx, ip, stack);
-#ifdef CONFIG_KPROBES
+
 		/*
 		 * Mark stacktraces with kretprobed functions on them
 		 * as unreliable.
 		 */
-		if (ip == (unsigned long)__kretprobe_trampoline)
+#ifdef CONFIG_RETHOOK
+		if (ip == (unsigned long)arch_rethook_trampoline)
 			return -EINVAL;
 #endif