powerpc/kprobes: Implement Optprobes

Current infrastructure of kprobe uses the unconditional trap instruction
to probe a running kernel. Optprobe allows kprobe to replace the trap
with a branch instruction to a detour buffer. Detour buffer contains
instructions to create an in memory pt_regs. Detour buffer also has a
call to optimized_callback() which in turn call the pre_handler(). After
the execution of the pre-handler, a call is made for instruction
emulation. The NIP is determined in advanced through dummy instruction
emulation and a branch instruction is created to the NIP at the end of
the trampoline.

To address the limitation of branch instruction in POWER architecture,
detour buffer slot is allocated from a reserved area. For the time
being, 64KB is reserved in memory for this purpose.

Instructions which can be emulated using analyse_instr() are the
candidates for optimization. Before optimization ensure that the address
range between the detour buffer allocated and the instruction being
probed is within +/- 32MB.

Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

2 files changed, 24 insertions, 1 deletions

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 75ee4f4..8ab9377 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -35,6 +35,7 @@ int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr);
 unsigned long branch_target(const unsigned int *instr);
 unsigned int translate_branch(const unsigned int *dest,
 			      const unsigned int *src);
+extern bool is_conditional_branch(unsigned int instr);
 #ifdef CONFIG_PPC_BOOK3E_64
 void __patch_exception(int exc, unsigned long addr);
 #define patch_exception(exc, name) do { \
diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
index 77885d8..d821835 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -40,7 +40,23 @@ struct pt_regs;
 struct kprobe;
 
 typedef ppc_opcode_t kprobe_opcode_t;
-#define MAX_INSN_SIZE 1
+
+extern kprobe_opcode_t optinsn_slot;
+
+/* Optinsn template address */
+extern kprobe_opcode_t optprobe_template_entry[];
+extern kprobe_opcode_t optprobe_template_op_address[];
+extern kprobe_opcode_t optprobe_template_call_handler[];
+extern kprobe_opcode_t optprobe_template_insn[];
+extern kprobe_opcode_t optprobe_template_call_emulate[];
+extern kprobe_opcode_t optprobe_template_ret[];
+extern kprobe_opcode_t optprobe_template_end[];
+
+/* Fixed instruction size for powerpc */
+#define MAX_INSN_SIZE		1
+#define MAX_OPTIMIZED_LENGTH	sizeof(kprobe_opcode_t)	/* 4 bytes */
+#define MAX_OPTINSN_SIZE	(optprobe_template_end - optprobe_template_entry)
+#define RELATIVEJUMP_SIZE	sizeof(kprobe_opcode_t)	/* 4 bytes */
 
 #ifdef PPC64_ELF_ABI_v2
 /* PPC64 ABIv2 needs local entry point */
@@ -126,6 +142,12 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
+struct arch_optimized_insn {
+	kprobe_opcode_t copied_insn[1];
+	/* detour buffer */
+	kprobe_opcode_t *insn;
+};
+
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 					unsigned long val, void *data);
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);