Commit df25edba authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov (AMD)
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230515093020.661756940@infradead.org
parent d42a2a89

arch/x86/include/asm/nops.h

+14 −2
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/alternative.c

+10 −0
Original line number Diff line number Diff line
@@ -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

};



/*

tools/arch/x86/include/asm/nops.h

+14 −2
Original line number Diff line number Diff line
@@ -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