[tip: x86/core] x86/kprobes: Fix to identify indirect jmp and others using range case

[tip-bot2 for Masami Hiramatsu]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     2f706e0e5e263c0d204e37ea496cbb0e98aac2d2
Gitweb:        https://git.kernel.org/tip/2f706e0e5e263c0d204e37ea496cbb0e98aac2d2
Author:        Masami Hiramatsu <mhiramat@xxxxxxxxxx>
AuthorDate:    Thu, 25 Mar 2021 19:08:43 +09:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 25 Mar 2021 11:37:22 +01:00

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@xxxxxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/161666692308.1120877.4675552834049546493.stgit@devnote2
---
 arch/x86/kernel/kprobes/core.c | 44 +++++++++++++++------------------
 1 file changed, 20 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 81e1432..922a6e2 100644
--- 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;
 	}
 }