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switch_to.h
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1 #ifndef _ASM_X86_SWITCH_TO_H
2 #define _ASM_X86_SWITCH_TO_H
3 
4 struct task_struct; /* one of the stranger aspects of C forward declarations */
6  struct task_struct *next);
7 struct tss_struct;
8 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
9  struct tss_struct *tss);
10 
11 #ifdef CONFIG_X86_32
12 
13 #ifdef CONFIG_CC_STACKPROTECTOR
14 #define __switch_canary \
15  "movl %P[task_canary](%[next]), %%ebx\n\t" \
16  "movl %%ebx, "__percpu_arg([stack_canary])"\n\t"
17 #define __switch_canary_oparam \
18  , [stack_canary] "=m" (stack_canary.canary)
19 #define __switch_canary_iparam \
20  , [task_canary] "i" (offsetof(struct task_struct, stack_canary))
21 #else /* CC_STACKPROTECTOR */
22 #define __switch_canary
23 #define __switch_canary_oparam
24 #define __switch_canary_iparam
25 #endif /* CC_STACKPROTECTOR */
26 
27 /*
28  * Saving eflags is important. It switches not only IOPL between tasks,
29  * it also protects other tasks from NT leaking through sysenter etc.
30  */
31 #define switch_to(prev, next, last) \
32 do { \
33  /* \
34  * Context-switching clobbers all registers, so we clobber \
35  * them explicitly, via unused output variables. \
36  * (EAX and EBP is not listed because EBP is saved/restored \
37  * explicitly for wchan access and EAX is the return value of \
38  * __switch_to()) \
39  */ \
40  unsigned long ebx, ecx, edx, esi, edi; \
41  \
42  asm volatile("pushfl\n\t" /* save flags */ \
43  "pushl %%ebp\n\t" /* save EBP */ \
44  "movl %%esp,%[prev_sp]\n\t" /* save ESP */ \
45  "movl %[next_sp],%%esp\n\t" /* restore ESP */ \
46  "movl $1f,%[prev_ip]\n\t" /* save EIP */ \
47  "pushl %[next_ip]\n\t" /* restore EIP */ \
48  __switch_canary \
49  "jmp __switch_to\n" /* regparm call */ \
50  "1:\t" \
51  "popl %%ebp\n\t" /* restore EBP */ \
52  "popfl\n" /* restore flags */ \
53  \
54  /* output parameters */ \
55  : [prev_sp] "=m" (prev->thread.sp), \
56  [prev_ip] "=m" (prev->thread.ip), \
57  "=a" (last), \
58  \
59  /* clobbered output registers: */ \
60  "=b" (ebx), "=c" (ecx), "=d" (edx), \
61  "=S" (esi), "=D" (edi) \
62  \
63  __switch_canary_oparam \
64  \
65  /* input parameters: */ \
66  : [next_sp] "m" (next->thread.sp), \
67  [next_ip] "m" (next->thread.ip), \
68  \
69  /* regparm parameters for __switch_to(): */ \
70  [prev] "a" (prev), \
71  [next] "d" (next) \
72  \
73  __switch_canary_iparam \
74  \
75  : /* reloaded segment registers */ \
76  "memory"); \
77 } while (0)
78 
79 #else /* CONFIG_X86_32 */
80 
81 /* frame pointer must be last for get_wchan */
82 #define SAVE_CONTEXT "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
83 #define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"
84 
85 #define __EXTRA_CLOBBER \
86  , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
87  "r12", "r13", "r14", "r15"
88 
89 #ifdef CONFIG_CC_STACKPROTECTOR
90 #define __switch_canary \
91  "movq %P[task_canary](%%rsi),%%r8\n\t" \
92  "movq %%r8,"__percpu_arg([gs_canary])"\n\t"
93 #define __switch_canary_oparam \
94  , [gs_canary] "=m" (irq_stack_union.stack_canary)
95 #define __switch_canary_iparam \
96  , [task_canary] "i" (offsetof(struct task_struct, stack_canary))
97 #else /* CC_STACKPROTECTOR */
98 #define __switch_canary
99 #define __switch_canary_oparam
100 #define __switch_canary_iparam
101 #endif /* CC_STACKPROTECTOR */
102 
103 /* Save restore flags to clear handle leaking NT */
104 #define switch_to(prev, next, last) \
105  asm volatile(SAVE_CONTEXT \
106  "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \
107  "movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */ \
108  "call __switch_to\n\t" \
109  "movq "__percpu_arg([current_task])",%%rsi\n\t" \
110  __switch_canary \
111  "movq %P[thread_info](%%rsi),%%r8\n\t" \
112  "movq %%rax,%%rdi\n\t" \
113  "testl %[_tif_fork],%P[ti_flags](%%r8)\n\t" \
114  "jnz ret_from_fork\n\t" \
115  RESTORE_CONTEXT \
116  : "=a" (last) \
117  __switch_canary_oparam \
118  : [next] "S" (next), [prev] "D" (prev), \
119  [threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
120  [ti_flags] "i" (offsetof(struct thread_info, flags)), \
121  [_tif_fork] "i" (_TIF_FORK), \
122  [thread_info] "i" (offsetof(struct task_struct, stack)), \
123  [current_task] "m" (current_task) \
124  __switch_canary_iparam \
125  : "memory", "cc" __EXTRA_CLOBBER)
126 
127 #endif /* CONFIG_X86_32 */
128 
129 #endif /* _ASM_X86_SWITCH_TO_H */