1/* SPDX-License-Identifier: GPL-2.0 */
 2/*
 3 * AT_SYSINFO entry point
 4*/
 5
 6#include <linux/linkage.h>
 7#include <asm/dwarf2.h>
 8#include <asm/cpufeatures.h>
 9#include <asm/alternative.h>
 
 
 
 
 
 
10
11	.text
12	.globl __kernel_vsyscall
13	.type __kernel_vsyscall,@function
14	ALIGN
15__kernel_vsyscall:
16	CFI_STARTPROC
17	/*
18	 * Reshuffle regs so that all of any of the entry instructions
19	 * will preserve enough state.
20	 *
21	 * A really nice entry sequence would be:
22	 *  pushl %edx
23	 *  pushl %ecx
24	 *  movl  %esp, %ecx
25	 *
26	 * Unfortunately, naughty Android versions between July and December
27	 * 2015 actually hardcode the traditional Linux SYSENTER entry
28	 * sequence.  That is severely broken for a number of reasons (ask
29	 * anyone with an AMD CPU, for example).  Nonetheless, we try to keep
30	 * it working approximately as well as it ever worked.
31	 *
32	 * This link may elucidate some of the history:
33	 *   https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7
34	 * personally, I find it hard to understand what's going on there.
35	 *
36	 * Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE.
37	 * Execute an indirect call to the address in the AT_SYSINFO auxv
38	 * entry.  That is the ONLY correct way to make a fast 32-bit system
39	 * call on Linux.  (Open-coding int $0x80 is also fine, but it's
40	 * slow.)
41	 */
42	pushl	%ecx
43	CFI_ADJUST_CFA_OFFSET	4
44	CFI_REL_OFFSET		ecx, 0
45	pushl	%edx
46	CFI_ADJUST_CFA_OFFSET	4
47	CFI_REL_OFFSET		edx, 0
48	pushl	%ebp
49	CFI_ADJUST_CFA_OFFSET	4
50	CFI_REL_OFFSET		ebp, 0
51
52	#define SYSENTER_SEQUENCE	"movl %esp, %ebp; sysenter"
53	#define SYSCALL_SEQUENCE	"movl %ecx, %ebp; syscall"
54
55#ifdef CONFIG_X86_64
56	/* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
57	ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \
58	                  SYSCALL_SEQUENCE,  X86_FEATURE_SYSCALL32
59#else
60	ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP
61#endif
62
63	/* Enter using int $0x80 */
64	int	$0x80
65SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL)
66
67	/*
68	 * Restore EDX and ECX in case they were clobbered.  EBP is not
69	 * clobbered (the kernel restores it), but it's cleaner and
70	 * probably faster to pop it than to adjust ESP using addl.
71	 */
72	popl	%ebp
73	CFI_RESTORE		ebp
74	CFI_ADJUST_CFA_OFFSET	-4
75	popl	%edx
76	CFI_RESTORE		edx
77	CFI_ADJUST_CFA_OFFSET	-4
78	popl	%ecx
79	CFI_RESTORE		ecx
80	CFI_ADJUST_CFA_OFFSET	-4
81	RET
82	CFI_ENDPROC
83
84	.size __kernel_vsyscall,.-__kernel_vsyscall
85	.previous

 
 1/*
 2 * AT_SYSINFO entry point
 3*/
 4
 
 5#include <asm/dwarf2.h>
 6#include <asm/cpufeatures.h>
 7#include <asm/alternative-asm.h>
 8
 9/*
10 * First get the common code for the sigreturn entry points.
11 * This must come first.
12 */
13#include "sigreturn.S"
14
15	.text
16	.globl __kernel_vsyscall
17	.type __kernel_vsyscall,@function
18	ALIGN
19__kernel_vsyscall:
20	CFI_STARTPROC
21	/*
22	 * Reshuffle regs so that all of any of the entry instructions
23	 * will preserve enough state.
24	 *
25	 * A really nice entry sequence would be:
26	 *  pushl %edx
27	 *  pushl %ecx
28	 *  movl  %esp, %ecx
29	 *
30	 * Unfortunately, naughty Android versions between July and December
31	 * 2015 actually hardcode the traditional Linux SYSENTER entry
32	 * sequence.  That is severely broken for a number of reasons (ask
33	 * anyone with an AMD CPU, for example).  Nonetheless, we try to keep
34	 * it working approximately as well as it ever worked.
35	 *
36	 * This link may eludicate some of the history:
37	 *   https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7
38	 * personally, I find it hard to understand what's going on there.
39	 *
40	 * Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE.
41	 * Execute an indirect call to the address in the AT_SYSINFO auxv
42	 * entry.  That is the ONLY correct way to make a fast 32-bit system
43	 * call on Linux.  (Open-coding int $0x80 is also fine, but it's
44	 * slow.)
45	 */
46	pushl	%ecx
47	CFI_ADJUST_CFA_OFFSET	4
48	CFI_REL_OFFSET		ecx, 0
49	pushl	%edx
50	CFI_ADJUST_CFA_OFFSET	4
51	CFI_REL_OFFSET		edx, 0
52	pushl	%ebp
53	CFI_ADJUST_CFA_OFFSET	4
54	CFI_REL_OFFSET		ebp, 0
55
56	#define SYSENTER_SEQUENCE	"movl %esp, %ebp; sysenter"
57	#define SYSCALL_SEQUENCE	"movl %ecx, %ebp; syscall"
58
59#ifdef CONFIG_X86_64
60	/* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
61	ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \
62	                  SYSCALL_SEQUENCE,  X86_FEATURE_SYSCALL32
63#else
64	ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP
65#endif
66
67	/* Enter using int $0x80 */
68	int	$0x80
69GLOBAL(int80_landing_pad)
70
71	/*
72	 * Restore EDX and ECX in case they were clobbered.  EBP is not
73	 * clobbered (the kernel restores it), but it's cleaner and
74	 * probably faster to pop it than to adjust ESP using addl.
75	 */
76	popl	%ebp
77	CFI_RESTORE		ebp
78	CFI_ADJUST_CFA_OFFSET	-4
79	popl	%edx
80	CFI_RESTORE		edx
81	CFI_ADJUST_CFA_OFFSET	-4
82	popl	%ecx
83	CFI_RESTORE		ecx
84	CFI_ADJUST_CFA_OFFSET	-4
85	ret
86	CFI_ENDPROC
87
88	.size __kernel_vsyscall,.-__kernel_vsyscall
89	.previous