[PATCH 1/4] sparc64: kprobes: Single-step from an executable instruction slot

[Stian Halseth <stian@itx.no>]

kprobes single-steps the probed instruction from kprobe->ainsn.insn[],
which is part of the kprobe itself and so lives in the linear mapping.
The sun4v linear mapping is not executable, and every probe hit oopses:

  sun4v_insn_access_exception: ADDR[fff800005b0cd66c] CTX[0000] TYPE[0006], going.

Allocate the slot with get_insn_slot(), as other architectures do. It
comes from executable memory in the module area.

Fixes: c4bce90ea2069 ("[SPARC64]: Deal with PTE layout differences in SUN4V.")
Closes: https://github.com/sparclinux/issues/issues/110
Signed-off-by: Stian Halseth <stian@itx.no>
---
 arch/sparc/include/asm/kprobes.h |  7 +++++--
 arch/sparc/kernel/kprobes.c      | 12 ++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/include/asm/kprobes.h b/arch/sparc/include/asm/kprobes.h
index aec742cd898f2..8cc9697846fa1 100644
--- a/arch/sparc/include/asm/kprobes.h
+++ b/arch/sparc/include/asm/kprobes.h
@@ -11,13 +11,16 @@
 #include <linux/types.h>
 #include <linux/percpu.h>
 
+#define __ARCH_WANT_KPROBES_INSN_SLOT
+
 typedef u32 kprobe_opcode_t;
 
 #define MAX_INSN_SIZE 2
 
 #define kretprobe_blacklist_size 0
 
-#define arch_remove_kprobe(p)	do {} while (0)
+struct kprobe;
+void arch_remove_kprobe(struct kprobe *p);
 
 #define flush_insn_slot(p)		\
 do { 	flushi(&(p)->ainsn.insn[0]);	\
@@ -29,7 +32,7 @@ void __kretprobe_trampoline(void);
 /* Architecture specific copy of original instruction*/
 struct arch_specific_insn {
 	/* copy of the original instruction */
-	kprobe_opcode_t insn[MAX_INSN_SIZE];
+	kprobe_opcode_t *insn;
 };
 
 struct prev_kprobe {
diff --git a/arch/sparc/kernel/kprobes.c b/arch/sparc/kernel/kprobes.c
index 191bbaca99212..608efda8cb948 100644
--- a/arch/sparc/kernel/kprobes.c
+++ b/arch/sparc/kernel/kprobes.c
@@ -52,6 +52,10 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	if ((unsigned long) p->addr & 0x3UL)
 		return -EILSEQ;
 
+	p->ainsn.insn = get_insn_slot();
+	if (!p->ainsn.insn)
+		return -ENOMEM;
+
 	p->ainsn.insn[0] = *p->addr;
 	flushi(&p->ainsn.insn[0]);
 
@@ -62,6 +66,14 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	return 0;
 }
 
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+	if (p->ainsn.insn) {
+		free_insn_slot(p->ainsn.insn, 0);
+		p->ainsn.insn = NULL;
+	}
+}
+
 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
 	*p->addr = BREAKPOINT_INSTRUCTION;
-- 
2.43.0