[tip:x86/urgent] x86/umip: Identify the STR and SLDT instructions

[tip-bot for Ricardo Neri]

Commit-ID:  6e2a3064d6a86094fecc20cd430fd96aaa801687
Gitweb:     https://git.kernel.org/tip/6e2a3064d6a86094fecc20cd430fd96aaa801687
Author:     Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
AuthorDate: Mon, 13 Nov 2017 22:29:44 -0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 14 Nov 2017 08:38:09 +0100

x86/umip: Identify the STR and SLDT instructions

The STR and SLDT instructions are not emulated by the UMIP code, thus
there's no functionality in the decoder to identify them.

However, a subsequent commit will introduce a warning about the use
of all the instructions that UMIP protect/changes, not only those that
are emulated.

A first step for that is to add the ability to decode/identify them.

Plus, now that STR and SLDT are identified, we need to explicitly avoid
their emulation (i.e., not rely on successful identification). Group
together all the cases that we do not want to emulate: STR, SLDT and user
long mode processes.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: ricardo.neri@xxxxxxxxx
Link: http://lkml.kernel.org/r/1510640985-18412-4-git-send-email-ricardo.neri-calderon@xxxxxxxxxxxxxxx
[ Rewrote the changelog, fixed ugly col80 artifact. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/umip.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 6ba82be..1f1f2d5 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -78,7 +78,9 @@
 
 #define	UMIP_INST_SGDT	0	/* 0F 01 /0 */
 #define	UMIP_INST_SIDT	1	/* 0F 01 /1 */
-#define	UMIP_INST_SMSW	3	/* 0F 01 /4 */
+#define	UMIP_INST_SMSW	2	/* 0F 01 /4 */
+#define	UMIP_INST_SLDT  3       /* 0F 00 /0 */
+#define	UMIP_INST_STR   4       /* 0F 00 /1 */
 
 /**
  * identify_insn() - Identify a UMIP-protected instruction
@@ -118,10 +120,16 @@ static int identify_insn(struct insn *insn)
 		default:
 			return -EINVAL;
 		}
+	} else if (insn->opcode.bytes[1] == 0x0) {
+		if (X86_MODRM_REG(insn->modrm.value) == 0)
+			return UMIP_INST_SLDT;
+		else if (X86_MODRM_REG(insn->modrm.value) == 1)
+			return UMIP_INST_STR;
+		else
+			return -EINVAL;
+	} else {
+		return -EINVAL;
 	}
-
-	/* SLDT AND STR are not emulated */
-	return -EINVAL;
 }
 
 /**
@@ -267,10 +275,6 @@ bool fixup_umip_exception(struct pt_regs *regs)
 	if (!regs)
 		return false;
 
-	/* Do not emulate 64-bit processes. */
-	if (user_64bit_mode(regs))
-		return false;
-
 	/*
 	 * If not in user-space long mode, a custom code segment could be in
 	 * use. This is true in protected mode (if the process defined a local
@@ -322,6 +326,10 @@ bool fixup_umip_exception(struct pt_regs *regs)
 	if (umip_inst < 0)
 		return false;
 
+	/* Do not emulate SLDT, STR or user long mode processes. */
+	if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
+		return false;
+
 	if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
 		return false;