x86/kprobes: Fix to identify indirect jmp and others using range case

Fix can_boost() to identify indirect jmp and others using range case
correctly.

Since the condition in switch statement is opcode & 0xf0, it can not
evaluate to 0xff case. This should be under the 0xf0 case. However,
there is no reason to use the conbinations of the bit-masked condition
and lower bit checking.

Use range case to clean up the switch statement too.

Fixes: 6256e668b7 ("x86/kprobes: Use int3 instead of debug trap for single-step")
Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/161666692308.1120877.4675552834049546493.stgit@devnote2

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 81e1432..922a6e2 100644 (file)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -164,32 +164,28 @@ int can_boost(struct insn *insn, void *addr)
 
        opcode = insn->opcode.bytes[0];
 
-       switch (opcode & 0xf0) {
-       case 0x60:
-               /* can't boost "bound" */
-               return (opcode != 0x62);
-       case 0x70:
-               return 0; /* can't boost conditional jump */
-       case 0x90:
-               return opcode != 0x9a;  /* can't boost call far */
-       case 0xc0:
-               /* can't boost software-interruptions */
-               return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
-       case 0xd0:
-               /* can boost AA* and XLAT */
-               return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
-       case 0xe0:
-               /* can boost in/out and absolute jmps */
-               return ((opcode & 0x04) || opcode == 0xea);
-       case 0xf0:
-               /* clear and set flags are boostable */
-               return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
-       case 0xff:
-               /* indirect jmp is boostable */
+       switch (opcode) {
+       case 0x62:              /* bound */
+       case 0x70 ... 0x7f:     /* Conditional jumps */
+       case 0x9a:              /* Call far */
+       case 0xc0 ... 0xc1:     /* Grp2 */
+       case 0xcc ... 0xce:     /* software exceptions */
+       case 0xd0 ... 0xd3:     /* Grp2 */
+       case 0xd6:              /* (UD) */
+       case 0xd8 ... 0xdf:     /* ESC */
+       case 0xe0 ... 0xe3:     /* LOOP*, JCXZ */
+       case 0xe8 ... 0xe9:     /* near Call, JMP */
+       case 0xeb:              /* Short JMP */
+       case 0xf0 ... 0xf4:     /* LOCK/REP, HLT */
+       case 0xf6 ... 0xf7:     /* Grp3 */
+       case 0xfe:              /* Grp4 */
+               /* ... are not boostable */
+               return 0;
+       case 0xff:              /* Grp5 */
+               /* Only indirect jmp is boostable */
                return X86_MODRM_REG(insn->modrm.bytes[0]) == 4;
        default:
-               /* call is not boostable */
-               return opcode != 0x9a;
+               return 1;
        }
 }