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Date:	Fri,  4 Jul 2014 15:03:45 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>
Subject: [PATCH 2/3] uprobes: fix 1-byte opcode tables

This change fixes 1-byte opcode tables so that only insns
for which we have real reasons to disallow probing are marked
with unset bits.

To that end:

Set bits for all prefix bytes. Their setting is ignored anyway -
we check the bitmap against OPCODE1(insn), not against first byte.
Keeping them set to 0 only confuses code reader with
"why we don't support that opcode" question.

Thus: enable bytes c4,c5 in 64-bit mode (VEX prefixes).
Byte 62 (EVEX prefix) is not yet enabled since insn decoder
does not support that yet.

For 32-bit mode, enable probing of opcodes 63 (arpl) and d6 (salc).
They don't require any special handling.

For 64-bit mode, disable 9a and ea - these undefined opcodes
were mistakenly left enabled.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Jim Keniston <jkenisto@...ibm.com>
CC: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
CC: Ingo Molnar <mingo@...nel.org>
CC: Oleg Nesterov <oleg@...hat.com>
---
 arch/x86/kernel/uprobes.c | 66 +++++++++++++----------------------------------
 1 file changed, 18 insertions(+), 48 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 9ba2fb2..40dfb4e 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -67,18 +67,6 @@
  * to keep gcc from statically optimizing it out, as variable_test_bit makes
  * some versions of gcc to think only *(unsigned long*) is used.
  *
- * Prefixes. Most marked as "bad", but it doesn't matter, since insn decoder
- * won't report *prefixes* as OPCODE1(insn).
- * 0f - 2-byte opcode prefix
- * 26,2e,36,3e - es:/cs:/ss:/ds:
- * 64 - fs: (marked as "good", why?)
- * 65 - gs: (marked as "good", why?)
- * 66 - operand-size prefix
- * 67 - address-size prefix
- * f0 - lock prefix
- * f2 - repnz    (marked as "good", why?)
- * f3 - rep/repz (marked as "good", why?)
- *
  * Opcodes we'll probably never support:
  * 6c-6f - ins,outs. SEGVs if used in userspace
  * e4-e7 - in,out imm. SEGVs if used in userspace
@@ -105,31 +93,27 @@
  *	Not supported since kernel's handling of userspace single-stepping
  *	(TF flag) is fragile.
  * cf - iret. Normally not used in userspace. Doesn't SEGV unless arguments are bad
- *
- * Opcodes which can be enabled right away:
- * 63 - arpl. This insn has no unusual exceptions (it's basically an arith op).
- * d6 - salc. Undocumented "sign-extend carry flag to AL" insn
  */
 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 static volatile u32 good_insns_32[256 / 32] = {
 	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
 	/*      ----------------------------------------------         */
-	W(0x00, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) | /* 00 */
+	W(0x00, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* 00 */
 	W(0x10, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) , /* 10 */
-	W(0x20, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1) | /* 20 */
-	W(0x30, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1) , /* 30 */
+	W(0x20, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 20 */
+	W(0x30, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 30 */
 	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
 	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
-	W(0x60, 1, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
+	W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
 	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */
 	W(0x80, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
 	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
 	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */
 	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
 	W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
-	W(0xd0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
+	W(0xd0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
 	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* e0 */
-	W(0xf0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
+	W(0xf0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
 	/*      ----------------------------------------------         */
 	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
 };
@@ -139,19 +123,6 @@ static volatile u32 good_insns_32[256 / 32] = {
 
 /* Good-instruction tables for 64-bit apps.
  *
- * Prefixes. Most marked as "bad", but it doesn't matter, since insn decoder
- * won't report *prefixes* as OPCODE1(insn).
- * 0f - 2-byte opcode prefix
- * 26,2e,36,3e - es:/cs:/ss:/ds:
- * 40-4f - rex prefixes
- * 64 - fs: (marked as "good", why?)
- * 65 - gs: (marked as "good", why?)
- * 66 - operand-size prefix
- * 67 - address-size prefix
- * f0 - lock prefix
- * f2 - repnz    (marked as "good", why?)
- * f3 - rep/repz (marked as "good", why?)
- *
  * Genuinely invalid opcodes:
  * 06,07 - formerly push/pop es
  * 0e - formerly push cs
@@ -159,14 +130,13 @@ static volatile u32 good_insns_32[256 / 32] = {
  * 1e,1f - formerly push/pop ds
  * 27,2f,37,3f - formerly daa/das/aaa/aas
  * 60,61 - formerly pusha/popa
- * 62 - formerly bound. EVEX prefix for AVX512
+ * 62 - formerly bound. EVEX prefix for AVX512 (not yet supported)
  * 82 - formerly redundant encoding of Group1
- * 9a - formerly call seg:ofs (marked as "supported"???)
- * c4,c5 - formerly les/lds. VEX prefixes for AVX
+ * 9a - formerly call seg:ofs
  * ce - formerly into
  * d4,d5 - formerly aam/aad
  * d6 - formerly undocumented salc
- * ea - formerly jmp seg:ofs (marked as "supported"???)
+ * ea - formerly jmp seg:ofs
  *
  * Opcodes we'll probably never support:
  * 6c-6f - ins,outs. SEGVs if used in userspace
@@ -190,22 +160,22 @@ static volatile u32 good_insns_32[256 / 32] = {
 static volatile u32 good_insns_64[256 / 32] = {
 	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
 	/*      ----------------------------------------------         */
-	W(0x00, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) | /* 00 */
+	W(0x00, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1) | /* 00 */
 	W(0x10, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 10 */
-	W(0x20, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) | /* 20 */
-	W(0x30, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 30 */
-	W(0x40, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 40 */
+	W(0x20, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) | /* 20 */
+	W(0x30, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) , /* 30 */
+	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
 	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
-	W(0x60, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
+	W(0x60, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
 	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */
 	W(0x80, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
-	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
+	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1) , /* 90 */
 	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */
 	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
-	W(0xc0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
+	W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
 	W(0xd0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
-	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* e0 */
-	W(0xf0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
+	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0) | /* e0 */
+	W(0xf0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
 	/*      ----------------------------------------------         */
 	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
 };
-- 
1.8.1.4

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