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authorPeter Zijlstra <peterz@infradead.org>2023-05-15 12:28:05 +0300
committerBorislav Petkov (AMD) <bp@alien8.de>2023-05-31 11:21:21 +0300
commitdf25edbac31ea87b488789d44a362063542b5967 (patch)
treeb1d07931c90fee18415cda9e054b7a710d2760ef /tools/arch
parentd42a2a89121071cc8dd285235253a4c739641635 (diff)
downloadlinux-df25edbac31ea87b488789d44a362063542b5967.tar.xz
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
Diffstat (limited to 'tools/arch')
-rw-r--r--tools/arch/x86/include/asm/nops.h16
1 files changed, 14 insertions, 2 deletions
diff --git a/tools/arch/x86/include/asm/nops.h b/tools/arch/x86/include/asm/nops.h
index c5573eaa5bb9..1c1b7550fa55 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