[PATCH v2 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[].
The array is embedded in struct kprobe, in the linear mapping. The
sun4v linear mapping is not executable. Every probe hit oopses:

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

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

flush_insn_slot() flushed the embedded copy after init_aggr_kprobe()
had copied it into the aggregator. The aggregator now shares the slot
by pointer. arch_prepare_kprobe() flushes the slot when it writes it.
Make the macro a no-op, like x86 and arm64.

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 | 12 ++++++------
 arch/sparc/kernel/kprobes.c      | 12 ++++++++++++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/sparc/include/asm/kprobes.h b/arch/sparc/include/asm/kprobes.h
index aec742cd898f2..d14206c063e25 100644
--- a/arch/sparc/include/asm/kprobes.h
+++ b/arch/sparc/include/asm/kprobes.h
@@ -11,25 +11,25 @@
 #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]);	\
-	flushi(&(p)->ainsn.insn[1]);	\
-} while (0)
+#define flush_insn_slot(p)	do { } while (0)
 
 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