arch/x86/lib/copy_user_64.S

/*
 * Copyright 2008 Vitaly Mayatskikh <vmayatsk@redhat.com>
 * Copyright 2002 Andi Kleen, SuSE Labs.
 * Subject to the GNU Public License v2.
 *
 * Functions to copy from and to user space.
 */

#include <linux/linkage.h>
#include <asm/dwarf2.h>

#define FIX_ALIGNMENT 1

#include <asm/current.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>

/*
 * By placing feature2 after feature1 in altinstructions section, we logically
 * implement:
 * If CPU has feature2, jmp to alt2 is used
 * else if CPU has feature1, jmp to alt1 is used
 * else jmp to orig is used.
 */
	.macro ALTERNATIVE_JUMP feature1,feature2,orig,alt1,alt2
0:
	.byte 0xe9	/* 32bit jump */
	.long \orig-1f	/* by default jump to orig */
1:
	.section .altinstr_replacement,"ax"
2:	.byte 0xe9			/* near jump with 32bit immediate */
	.long \alt1-1b /* offset */   /* or alternatively to alt1 */
3:	.byte 0xe9			/* near jump with 32bit immediate */
	.long \alt2-1b /* offset */   /* or alternatively to alt2 */
	.previous

	.section .altinstructions,"a"
	altinstruction_entry 0b,2b,\feature1,5,5
	altinstruction_entry 0b,3b,\feature2,5,5
	.previous
	.endm

	.macro ALIGN_DESTINATION
#ifdef FIX_ALIGNMENT
	/* check for bad alignment of destination */
	movl %edi,%ecx
	andl $7,%ecx
	jz 102f				/* already aligned */
	subl $8,%ecx
	negl %ecx
	subl %ecx,%edx
100:	movb (%rsi),%al
101:	movb %al,(%rdi)
	incq %rsi
	incq %rdi
	decl %ecx
	jnz 100b
102:
	.section .fixup,"ax"
103:	addl %ecx,%edx			/* ecx is zerorest also */
	jmp copy_user_handle_tail
	.previous

	.section __ex_table,"a"
	.align 8
	.quad 100b,103b
	.quad 101b,103b
	.previous
#endif
	.endm

/* Standard copy_to_user with segment limit checking */
ENTRY(_copy_to_user)
	CFI_STARTPROC
	GET_THREAD_INFO(%rax)
	movq %rdi,%rcx
	addq %rdx,%rcx
	jc bad_to_user
	cmpq TI_addr_limit(%rax),%rcx
	ja bad_to_user
	ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,X86_FEATURE_ERMS,	\
		copy_user_generic_unrolled,copy_user_generic_string,	\
		copy_user_enhanced_fast_string
	CFI_ENDPROC
ENDPROC(_copy_to_user)

/* Standard copy_from_user with segment limit checking */
ENTRY(_copy_from_user)
	CFI_STARTPROC
	GET_THREAD_INFO(%rax)
	movq %rsi,%rcx
	addq %rdx,%rcx
	jc bad_from_user
	cmpq TI_addr_limit(%rax),%rcx
	ja bad_from_user
	ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,X86_FEATURE_ERMS,	\
		copy_user_generic_unrolled,copy_user_generic_string,	\
		copy_user_enhanced_fast_string
	CFI_ENDPROC
ENDPROC(_copy_from_user)

	.section .fixup,"ax"
	/* must zero dest */
ENTRY(bad_from_user)
bad_from_user:
	CFI_STARTPROC
	movl %edx,%ecx
	xorl %eax,%eax
	rep
	stosb
bad_to_user:
	movl %edx,%eax
	ret
	CFI_ENDPROC
ENDPROC(bad_from_user)
	.previous

/*
 * copy_user_generic_unrolled - memory copy with exception handling.
 * This version is for CPUs like P4 that don't have efficient micro
 * code for rep movsq
 *
 * Input:
 * rdi destination
 * rsi source
 * rdx count
 *
 * Output:
 * eax uncopied bytes or 0 if successful.
 */
ENTRY(copy_user_generic_unrolled)
	CFI_STARTPROC
	cmpl $8,%edx
	jb 20f		/* less then 8 bytes, go to byte copy loop */
	ALIGN_DESTINATION
	movl %edx,%ecx
	andl $63,%edx
	shrl $6,%ecx
	jz 17f
1:	movq (%rsi),%r8
2:	movq 1*8(%rsi),%r9
3:	movq 2*8(%rsi),%r10
4:	movq 3*8(%rsi),%r11
5:	movq %r8,(%rdi)
6:	movq %r9,1*8(%rdi)
7:	movq %r10,2*8(%rdi)
8:	movq %r11,3*8(%rdi)
9:	movq 4*8(%rsi),%r8
10:	movq 5*8(%rsi),%r9
11:	movq 6*8(%rsi),%r10
12:	movq 7*8(%rsi),%r11
13:	movq %r8,4*8(%rdi)
14:	movq %r9,5*8(%rdi)
15:	movq %r10,6*8(%rdi)
16:	movq %r11,7*8(%rdi)
	leaq 64(%rsi),%rsi
	leaq 64(%rdi),%rdi
	decl %ecx
	jnz 1b
17:	movl %edx,%ecx
	andl $7,%edx
	shrl $3,%ecx
	jz 20f
18:	movq (%rsi),%r8
19:	movq %r8,(%rdi)
	leaq 8(%rsi),%rsi
	leaq 8(%rdi),%rdi
	decl %ecx
	jnz 18b
20:	andl %edx,%edx
	jz 23f
	movl %edx,%ecx
21:	movb (%rsi),%al
22:	movb %al,(%rdi)
	incq %rsi
	incq %rdi
	decl %ecx
	jnz 21b
23:	xor %eax,%eax
	ret

	.section .fixup,"ax"
30:	shll $6,%ecx
	addl %ecx,%edx
	jmp 60f
40:	lea (%rdx,%rcx,8),%rdx
	jmp 60f
50:	movl %ecx,%edx
60:	jmp copy_user_handle_tail /* ecx is zerorest also */
	.previous

	.section __ex_table,"a"
	.align 8
	.quad 1b,30b
	.quad 2b,30b
	.quad 3b,30b
	.quad 4b,30b
	.quad 5b,30b
	.quad 6b,30b
	.quad 7b,30b
	.quad 8b,30b
	.quad 9b,30b
	.quad 10b,30b
	.quad 11b,30b
	.quad 12b,30b
	.quad 13b,30b
	.quad 14b,30b
	.quad 15b,30b
	.quad 16b,30b
	.quad 18b,40b
	.quad 19b,40b
	.quad 21b,50b
	.quad 22b,50b
	.previous
	CFI_ENDPROC
ENDPROC(copy_user_generic_unrolled)

/* Some CPUs run faster using the string copy instructions.
 * This is also a lot simpler. Use them when possible.
 *
 * Only 4GB of copy is supported. This shouldn't be a problem
 * because the kernel normally only writes from/to page sized chunks
 * even if user space passed a longer buffer.
 * And more would be dangerous because both Intel and AMD have
 * errata with rep movsq > 4GB. If someone feels the need to fix
 * this please consider this.
 *
 * Input:
 * rdi destination
 * rsi source
 * rdx count
 *
 * Output:
 * eax uncopied bytes or 0 if successful.
 */
ENTRY(copy_user_generic_string)
	CFI_STARTPROC
	andl %edx,%edx
	jz 4f
	cmpl $8,%edx
	jb 2f		/* less than 8 bytes, go to byte copy loop */
	ALIGN_DESTINATION
	movl %edx,%ecx
	shrl $3,%ecx
	andl $7,%edx
1:	rep
	movsq
2:	movl %edx,%ecx
3:	rep
	movsb
4:	xorl %eax,%eax
	ret

	.section .fixup,"ax"
11:	lea (%rdx,%rcx,8),%rcx
12:	movl %ecx,%edx		/* ecx is zerorest also */
	jmp copy_user_handle_tail
	.previous

	.section __ex_table,"a"
	.align 8
	.quad 1b,11b
	.quad 3b,12b
	.previous
	CFI_ENDPROC
ENDPROC(copy_user_generic_string)

/*
 * Some CPUs are adding enhanced REP MOVSB/STOSB instructions.
 * It's recommended to use enhanced REP MOVSB/STOSB if it's enabled.
 *
 * Input:
 * rdi destination
 * rsi source
 * rdx count
 *
 * Output:
 * eax uncopied bytes or 0 if successful.
 */
ENTRY(copy_user_enhanced_fast_string)
	CFI_STARTPROC
	andl %edx,%edx
	jz 2f
	movl %edx,%ecx
1:	rep
	movsb
2:	xorl %eax,%eax
	ret

	.section .fixup,"ax"
12:	movl %ecx,%edx		/* ecx is zerorest also */
	jmp copy_user_handle_tail
	.previous

	.section __ex_table,"a"
	.align 8
	.quad 1b,12b
	.previous
	CFI_ENDPROC
ENDPROC(copy_user_enhanced_fast_string)