[PATCH -tip 2/2] x86/kprobes: Fix to identify indirect jmp and others using range case

From: Masami Hiramatsu <mhiramat@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
	Colin Ian King <colin.king@canonical.com>,
	dan.carpenter@oracle.com,
	Muhammad Usama Anjum <musamaanjum@gmail.com>
Subject: [PATCH -tip 2/2] x86/kprobes: Fix to identify indirect jmp and others using range case
Date: Thu, 25 Mar 2021 19:08:43 +0900	[thread overview]
Message-ID: <161666692308.1120877.4675552834049546493.stgit@devnote2> (raw)
In-Reply-To: <161666690060.1120877.4569379871114610764.stgit@devnote2>

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>
---
 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 503958f15cf9..c1c763840d6e 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;
 	}
 }
 

