[PATCH] parisc: Avoid using hardware single-step in kprobes

[Helge Deller <deller@xxxxxx>]

This patch changes the kprobe and kretprobe feature to use another
break instruction instead of relying on the hardware single-step
feature.
That way those kprobes now work in qemu as well, because in qemu we
don't emulate yet single-stepping.

Signed-off-by: Helge Deller <deller@xxxxxx>

diff --git a/arch/parisc/include/asm/kprobes.h b/arch/parisc/include/asm/kprobes.h
index 904034da4974..0a175ac87698 100644
--- a/arch/parisc/include/asm/kprobes.h
+++ b/arch/parisc/include/asm/kprobes.h
@@ -18,8 +18,9 @@
 #include <linux/notifier.h>

 #define PARISC_KPROBES_BREAK_INSN	0x3ff801f
+#define PARISC_KPROBES_BREAK_INSN2	0x3ff801e
 #define  __ARCH_WANT_KPROBES_INSN_SLOT
-#define MAX_INSN_SIZE 1
+#define MAX_INSN_SIZE 2

 typedef u32 kprobe_opcode_t;
 struct kprobe;
@@ -29,7 +30,7 @@ void arch_remove_kprobe(struct kprobe *p);
 #define flush_insn_slot(p) \
 	flush_icache_range((unsigned long)&(p)->ainsn.insn[0], \
 			   (unsigned long)&(p)->ainsn.insn[0] + \
-			   sizeof(kprobe_opcode_t))
+			   MAX_INSN_SIZE*sizeof(kprobe_opcode_t))

 #define kretprobe_blacklist_size    0

diff --git a/arch/parisc/kernel/kprobes.c b/arch/parisc/kernel/kprobes.c
index e2bdb5a5f93e..2ca34fc250a6 100644
--- a/arch/parisc/kernel/kprobes.c
+++ b/arch/parisc/kernel/kprobes.c
@@ -5,6 +5,7 @@
  * PA-RISC kprobes implementation
  *
  * Copyright (c) 2019 Sven Schnelle <svens@xxxxxxxxxxxxxx>
+ * Copyright (c) 2021 Helge Deller <deller@xxxxxx>
  */

 #include <linux/types.h>
@@ -25,9 +26,14 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	if (!p->ainsn.insn)
 		return -ENOMEM;

-	memcpy(p->ainsn.insn, p->addr,
-		MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	/*
+	 * Set up new instructions. Second break instruction will
+	 * trigger call of parisc_kprobe_ss_handler().
+	 */
 	p->opcode = *p->addr;
+	p->ainsn.insn[0] = p->opcode;
+	p->ainsn.insn[1] = PARISC_KPROBES_BREAK_INSN2;
+
 	flush_insn_slot(p);
 	return 0;
 }
@@ -73,9 +79,7 @@ static void __kprobes setup_singlestep(struct kprobe *p,
 {
 	kcb->iaoq[0] = regs->iaoq[0];
 	kcb->iaoq[1] = regs->iaoq[1];
-	regs->iaoq[0] = (unsigned long)p->ainsn.insn;
-	mtctl(0, 0);
-	regs->gr[0] |= PSW_R;
+	instruction_pointer_set(regs, (unsigned long)p->ainsn.insn);
 }

 int __kprobes parisc_kprobe_break_handler(struct pt_regs *regs)
@@ -165,9 +170,8 @@ int __kprobes parisc_kprobe_ss_handler(struct pt_regs *regs)
 		regs->iaoq[0] = kcb->iaoq[1];
 		break;
 	default:
-		regs->iaoq[1] = kcb->iaoq[0];
-		regs->iaoq[1] += (regs->iaoq[1] - regs->iaoq[0]) + 4;
 		regs->iaoq[0] = kcb->iaoq[1];
+		regs->iaoq[1] = regs->iaoq[0] + 4;
 		break;
 	}
 	kcb->kprobe_status = KPROBE_HIT_SSDONE;
@@ -191,14 +195,17 @@ static struct kprobe trampoline_p = {
 static int __kprobes trampoline_probe_handler(struct kprobe *p,
 					      struct pt_regs *regs)
 {
-	unsigned long orig_ret_address;
-
-	orig_ret_address = __kretprobe_trampoline_handler(regs, NULL);
-	instruction_pointer_set(regs, orig_ret_address);
+	__kretprobe_trampoline_handler(regs, NULL);

 	return 1;
 }

+void arch_kretprobe_fixup_return(struct pt_regs *regs,
+				 kprobe_opcode_t *correct_ret_addr)
+{
+	regs->gr[2] = (unsigned long)correct_ret_addr;
+}
+
 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 				      struct pt_regs *regs)
 {
diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index b11fb26ce299..3ec3be8e90c5 100644
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -302,7 +302,10 @@ static void handle_break(struct pt_regs *regs)
 		parisc_kprobe_break_handler(regs);
 		return;
 	}
-
+	if (unlikely(iir == PARISC_KPROBES_BREAK_INSN2)) {
+		parisc_kprobe_ss_handler(regs);
+		return;
+	}
 #endif

 #ifdef CONFIG_KGDB
@@ -539,11 +542,6 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
 		/* Recovery counter trap */
 		regs->gr[0] &= ~PSW_R;

-#ifdef CONFIG_KPROBES
-		if (parisc_kprobe_ss_handler(regs))
-			return;
-#endif
-
 #ifdef CONFIG_KGDB
 		if (kgdb_single_step) {
 			kgdb_handle_exception(0, SIGTRAP, 0, regs);