[PATCH v3 12/14] powerpc/uprobes: Add support for prefixed instructions

[Jordan Niethe <jniethe5@gmail.com>]

Uprobes can execute instructions out of line. Increase the size of the
buffer used  for this so that this works for prefixed instructions. Take
into account the length of prefixed instructions when fixing up the nip.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
v2: - Fix typo
    - Use macro for instruction length
---
 arch/powerpc/include/asm/uprobes.h | 16 ++++++++++++----
 arch/powerpc/kernel/uprobes.c      |  4 ++--
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/uprobes.h b/arch/powerpc/include/asm/uprobes.h
index 2bbdf27d09b5..5516ab27db47 100644
--- a/arch/powerpc/include/asm/uprobes.h
+++ b/arch/powerpc/include/asm/uprobes.h
@@ -14,18 +14,26 @@
 
 typedef ppc_opcode_t uprobe_opcode_t;
 
+/*
+ * Ensure we have enough space for prefixed instructions, which
+ * are double the size of a word instruction, i.e. 8 bytes.
+ */
 #define MAX_UINSN_BYTES		4
-#define UPROBE_XOL_SLOT_BYTES	(MAX_UINSN_BYTES)
+#define UPROBE_XOL_SLOT_BYTES	(2 * MAX_UINSN_BYTES)
 
 /* The following alias is needed for reference from arch-agnostic code */
 #define UPROBE_SWBP_INSN	BREAKPOINT_INSTRUCTION
 #define UPROBE_SWBP_INSN_SIZE	4 /* swbp insn size in bytes */
 
 struct arch_uprobe {
+	 /*
+	  * Ensure there is enough space for prefixed instructions. Prefixed
+	  * instructions must not cross 64-byte boundaries.
+	  */
 	union {
-		u32	insn;
-		u32	ixol;
-	};
+		uprobe_opcode_t	insn[2];
+		uprobe_opcode_t	ixol[2];
+	} __aligned(64);
 };
 
 struct arch_uprobe_task {
diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
index 4ab40c4b576f..7e0334ad5cfe 100644
--- a/arch/powerpc/kernel/uprobes.c
+++ b/arch/powerpc/kernel/uprobes.c
@@ -111,7 +111,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	 * support doesn't exist and have to fix-up the next instruction
 	 * to be executed.
 	 */
-	regs->nip = utask->vaddr + MAX_UINSN_BYTES;
+	regs->nip = utask->vaddr + PPC_INST_LENGTH(auprobe->insn[0]);
 
 	user_disable_single_step(current);
 	return 0;
@@ -173,7 +173,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	 * emulate_step() returns 1 if the insn was successfully emulated.
 	 * For all other cases, we need to single-step in hardware.
 	 */
-	ret = emulate_step(regs, auprobe->insn, PPC_NO_SUFFIX);
+	ret = emulate_step(regs, auprobe->insn[0], auprobe->insn[1]);
 	if (ret > 0)
 		return true;
 
-- 
2.17.1