[RFC PATCH tip/master V3 3/8] kprobes/x86: Use instruction decoder for booster

[Masami Hiramatsu]

Use x86 instruction decoder for checking whether the probed
instruction is able to boost or not, instead of hand-written
code.

Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
---
 arch/x86/kernel/kprobes/core.c |   39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 81d4dc7..6327f95 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -169,35 +169,33 @@ NOKPROBE_SYMBOL(skip_prefixes);
  */
 int can_boost(kprobe_opcode_t *opcodes, void *addr)
 {
+       struct insn insn;
        kprobe_opcode_t opcode;
-       kprobe_opcode_t *orig_opcodes = opcodes;
 
        if (search_exception_tables((unsigned long)addr))
                return 0;       /* Page fault may occur on this address. */
 
-retry:
-       if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
-               return 0;
-       opcode = *(opcodes++);
+       kernel_insn_init(&insn, (void *)opcodes, MAX_INSN_SIZE);
+       insn_get_opcode(&insn);
 
        /* 2nd-byte opcode */
-       if (opcode == 0x0f) {
-               if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
-                       return 0;
-               return test_bit(*opcodes,
+       if (insn.opcode.nbytes == 2)
+               return test_bit(insn.opcode.bytes[1],
                                (unsigned long *)twobyte_is_boostable);
-       }
+
+       if (insn.opcode.nbytes != 1)
+               return 0;
+
+       /* Can't boost Address-size override prefix */
+       if (unlikely(inat_is_address_size_prefix(insn.attr)))
+               return 0;
+
+       opcode = insn.opcode.bytes[0];
 
        switch (opcode & 0xf0) {
-#ifdef CONFIG_X86_64
-       case 0x40:
-               goto retry; /* REX prefix is boostable */
-#endif
        case 0x60:
-               if (0x63 < opcode && opcode < 0x67)
-                       goto retry; /* prefixes */
-               /* can't boost Address-size override and bound */
-               return (opcode != 0x62 && opcode != 0x67);
+               /* can't boost "bound" */
+               return (opcode != 0x62);
        case 0x70:
                return 0; /* can't boost conditional jump */
        case 0x90:
@@ -212,14 +210,9 @@ int can_boost(kprobe_opcode_t *opcodes, void *addr)
                /* can boost in/out and absolute jmps */
                return ((opcode & 0x04) || opcode == 0xea);
        case 0xf0:
-               if ((opcode & 0x0c) == 0 && opcode != 0xf1)
-                       goto retry; /* lock/rep(ne) prefix */
                /* clear and set flags are boostable */
                return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
        default:
-               /* segment override prefixes are boostable */
-               if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
-                       goto retry; /* prefixes */
                /* CS override prefix and call are not boostable */
                return (opcode != 0x2e && opcode != 0x9a);
        }