diff mbox series

[tip:,x86/alternatives] x86/alternatives: Add longer 64-bit NOPs

Message ID 168553423659.404.5660759235465936351.tip-bot2@tip-bot2
State New
Headers
Series [tip:,x86/alternatives] x86/alternatives: Add longer 64-bit NOPs |

Commit Message

tip-bot2 for Thomas Gleixner May 31, 2023, 11:57 a.m. UTC 
  The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     df25edbac31ea87b488789d44a362063542b5967
Gitweb:        https://git.kernel.org/tip/df25edbac31ea87b488789d44a362063542b5967
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Mon, 15 May 2023 11:28:05 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Wed, 31 May 2023 10:21:21 +02:00

x86/alternatives: Add longer 64-bit NOPs

By adding support for longer NOPs there are a few more alternatives
that can turn into a single instruction.

Add up to NOP11, the same limit where GNU as .nops also stops
generating longer nops. This is because a number of uarchs have severe
decode penalties for more than 3 prefixes.

  [ bp: Sync up with the version in tools/ while at it. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230515093020.661756940@infradead.org
---
 arch/x86/include/asm/nops.h       | 16 ++++++++++++++--
 arch/x86/kernel/alternative.c     | 10 ++++++++++
 tools/arch/x86/include/asm/nops.h | 16 ++++++++++++++--
 3 files changed, 38 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/include/asm/nops.h b/arch/x86/include/asm/nops.h
index c5573ea..1c1b755 100644
--- a/arch/x86/include/asm/nops.h
+++ b/arch/x86/include/asm/nops.h
@@ -34,6 +34,8 @@ 
 #define BYTES_NOP7	0x8d,0xb4,0x26,0x00,0x00,0x00,0x00
 #define BYTES_NOP8	0x3e,BYTES_NOP7
 
+#define ASM_NOP_MAX 8
+
 #else
 
 /*
@@ -47,6 +49,9 @@ 
  * 6: osp nopl 0x00(%eax,%eax,1)
  * 7: nopl 0x00000000(%eax)
  * 8: nopl 0x00000000(%eax,%eax,1)
+ * 9: cs nopl 0x00000000(%eax,%eax,1)
+ * 10: osp cs nopl 0x00000000(%eax,%eax,1)
+ * 11: osp osp cs nopl 0x00000000(%eax,%eax,1)
  */
 #define BYTES_NOP1	0x90
 #define BYTES_NOP2	0x66,BYTES_NOP1
@@ -56,6 +61,15 @@ 
 #define BYTES_NOP6	0x66,BYTES_NOP5
 #define BYTES_NOP7	0x0f,0x1f,0x80,0x00,0x00,0x00,0x00
 #define BYTES_NOP8	0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00
+#define BYTES_NOP9	0x2e,BYTES_NOP8
+#define BYTES_NOP10	0x66,BYTES_NOP9
+#define BYTES_NOP11	0x66,BYTES_NOP10
+
+#define ASM_NOP9  _ASM_BYTES(BYTES_NOP9)
+#define ASM_NOP10 _ASM_BYTES(BYTES_NOP10)
+#define ASM_NOP11 _ASM_BYTES(BYTES_NOP11)
+
+#define ASM_NOP_MAX 11
 
 #endif /* CONFIG_64BIT */
 
@@ -68,8 +82,6 @@ 
 #define ASM_NOP7 _ASM_BYTES(BYTES_NOP7)
 #define ASM_NOP8 _ASM_BYTES(BYTES_NOP8)
 
-#define ASM_NOP_MAX 8
-
 #ifndef __ASSEMBLY__
 extern const unsigned char * const x86_nops[];
 #endif
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 93aa95a..0747d29 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -98,6 +98,11 @@  static const unsigned char x86nops[] =
 	BYTES_NOP6,
 	BYTES_NOP7,
 	BYTES_NOP8,
+#ifdef CONFIG_64BIT
+	BYTES_NOP9,
+	BYTES_NOP10,
+	BYTES_NOP11,
+#endif
 };
 
 const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
@@ -111,6 +116,11 @@  const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
 	x86nops + 1 + 2 + 3 + 4 + 5,
 	x86nops + 1 + 2 + 3 + 4 + 5 + 6,
 	x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
+#ifdef CONFIG_64BIT
+	x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
+	x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9,
+	x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10,
+#endif
 };
 
 /*
diff --git a/tools/arch/x86/include/asm/nops.h b/tools/arch/x86/include/asm/nops.h
index c5573ea..1c1b755 100644
--- a/tools/arch/x86/include/asm/nops.h
+++ b/tools/arch/x86/include/asm/nops.h
@@ -34,6 +34,8 @@ 
 #define BYTES_NOP7	0x8d,0xb4,0x26,0x00,0x00,0x00,0x00
 #define BYTES_NOP8	0x3e,BYTES_NOP7
 
+#define ASM_NOP_MAX 8
+
 #else
 
 /*
@@ -47,6 +49,9 @@ 
  * 6: osp nopl 0x00(%eax,%eax,1)
  * 7: nopl 0x00000000(%eax)
  * 8: nopl 0x00000000(%eax,%eax,1)
+ * 9: cs nopl 0x00000000(%eax,%eax,1)
+ * 10: osp cs nopl 0x00000000(%eax,%eax,1)
+ * 11: osp osp cs nopl 0x00000000(%eax,%eax,1)
  */
 #define BYTES_NOP1	0x90
 #define BYTES_NOP2	0x66,BYTES_NOP1
@@ -56,6 +61,15 @@ 
 #define BYTES_NOP6	0x66,BYTES_NOP5
 #define BYTES_NOP7	0x0f,0x1f,0x80,0x00,0x00,0x00,0x00
 #define BYTES_NOP8	0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00
+#define BYTES_NOP9	0x2e,BYTES_NOP8
+#define BYTES_NOP10	0x66,BYTES_NOP9
+#define BYTES_NOP11	0x66,BYTES_NOP10
+
+#define ASM_NOP9  _ASM_BYTES(BYTES_NOP9)
+#define ASM_NOP10 _ASM_BYTES(BYTES_NOP10)
+#define ASM_NOP11 _ASM_BYTES(BYTES_NOP11)
+
+#define ASM_NOP_MAX 11
 
 #endif /* CONFIG_64BIT */
 
@@ -68,8 +82,6 @@ 
 #define ASM_NOP7 _ASM_BYTES(BYTES_NOP7)
 #define ASM_NOP8 _ASM_BYTES(BYTES_NOP8)
 
-#define ASM_NOP_MAX 8
-
 #ifndef __ASSEMBLY__
 extern const unsigned char * const x86_nops[];
 #endif