Commit | Line | Data |
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fa1e03ea RM |
1 | /* |
2 | * x86 single-step support code, common to 32-bit and 64-bit. | |
3 | */ | |
4 | #include <linux/sched.h> | |
5 | #include <linux/mm.h> | |
6 | #include <linux/ptrace.h> | |
254e0a6b | 7 | #include <asm/desc.h> |
fa1e03ea | 8 | |
37cd9cf3 | 9 | unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) |
fa1e03ea RM |
10 | { |
11 | unsigned long addr, seg; | |
12 | ||
65ea5b03 | 13 | addr = regs->ip; |
fa1e03ea | 14 | seg = regs->cs & 0xffff; |
65ea5b03 | 15 | if (v8086_mode(regs)) { |
7122ec81 RM |
16 | addr = (addr & 0xffff) + (seg << 4); |
17 | return addr; | |
18 | } | |
fa1e03ea RM |
19 | |
20 | /* | |
21 | * We'll assume that the code segments in the GDT | |
22 | * are all zero-based. That is largely true: the | |
23 | * TLS segments are used for data, and the PNPBIOS | |
24 | * and APM bios ones we just ignore here. | |
25 | */ | |
3f80c1ad | 26 | if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { |
254e0a6b | 27 | struct desc_struct *desc; |
fa1e03ea RM |
28 | unsigned long base; |
29 | ||
30 | seg &= ~7UL; | |
31 | ||
32 | mutex_lock(&child->mm->context.lock); | |
33 | if (unlikely((seg >> 3) >= child->mm->context.size)) | |
34 | addr = -1L; /* bogus selector, access would fault */ | |
35 | else { | |
36 | desc = child->mm->context.ldt + seg; | |
254e0a6b | 37 | base = get_desc_base(desc); |
fa1e03ea RM |
38 | |
39 | /* 16-bit code segment? */ | |
254e0a6b | 40 | if (!desc->d) |
fa1e03ea RM |
41 | addr &= 0xffff; |
42 | addr += base; | |
43 | } | |
44 | mutex_unlock(&child->mm->context.lock); | |
45 | } | |
46 | ||
47 | return addr; | |
48 | } | |
49 | ||
50 | static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) | |
51 | { | |
52 | int i, copied; | |
53 | unsigned char opcode[15]; | |
37cd9cf3 | 54 | unsigned long addr = convert_ip_to_linear(child, regs); |
fa1e03ea RM |
55 | |
56 | copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0); | |
57 | for (i = 0; i < copied; i++) { | |
58 | switch (opcode[i]) { | |
59 | /* popf and iret */ | |
60 | case 0x9d: case 0xcf: | |
61 | return 1; | |
62 | ||
63 | /* CHECKME: 64 65 */ | |
64 | ||
65 | /* opcode and address size prefixes */ | |
66 | case 0x66: case 0x67: | |
67 | continue; | |
68 | /* irrelevant prefixes (segment overrides and repeats) */ | |
69 | case 0x26: case 0x2e: | |
70 | case 0x36: case 0x3e: | |
71 | case 0x64: case 0x65: | |
5f76cb1f | 72 | case 0xf0: case 0xf2: case 0xf3: |
fa1e03ea RM |
73 | continue; |
74 | ||
7122ec81 | 75 | #ifdef CONFIG_X86_64 |
fa1e03ea RM |
76 | case 0x40 ... 0x4f: |
77 | if (regs->cs != __USER_CS) | |
78 | /* 32-bit mode: register increment */ | |
79 | return 0; | |
80 | /* 64-bit mode: REX prefix */ | |
81 | continue; | |
7122ec81 | 82 | #endif |
fa1e03ea RM |
83 | |
84 | /* CHECKME: f2, f3 */ | |
85 | ||
86 | /* | |
87 | * pushf: NOTE! We should probably not let | |
88 | * the user see the TF bit being set. But | |
89 | * it's more pain than it's worth to avoid | |
90 | * it, and a debugger could emulate this | |
91 | * all in user space if it _really_ cares. | |
92 | */ | |
93 | case 0x9c: | |
94 | default: | |
95 | return 0; | |
96 | } | |
97 | } | |
98 | return 0; | |
99 | } | |
100 | ||
10faa81e RM |
101 | /* |
102 | * Enable single-stepping. Return nonzero if user mode is not using TF itself. | |
103 | */ | |
104 | static int enable_single_step(struct task_struct *child) | |
fa1e03ea RM |
105 | { |
106 | struct pt_regs *regs = task_pt_regs(child); | |
6718d0d6 | 107 | unsigned long oflags; |
fa1e03ea | 108 | |
380fdd75 RM |
109 | /* |
110 | * If we stepped into a sysenter/syscall insn, it trapped in | |
111 | * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. | |
112 | * If user-mode had set TF itself, then it's still clear from | |
113 | * do_debug() and we need to set it again to restore the user | |
114 | * state so we don't wrongly set TIF_FORCED_TF below. | |
115 | * If enable_single_step() was used last and that is what | |
116 | * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are | |
117 | * already set and our bookkeeping is fine. | |
118 | */ | |
119 | if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) | |
120 | regs->flags |= X86_EFLAGS_TF; | |
121 | ||
fa1e03ea RM |
122 | /* |
123 | * Always set TIF_SINGLESTEP - this guarantees that | |
124 | * we single-step system calls etc.. This will also | |
125 | * cause us to set TF when returning to user mode. | |
126 | */ | |
127 | set_tsk_thread_flag(child, TIF_SINGLESTEP); | |
128 | ||
6718d0d6 | 129 | oflags = regs->flags; |
fa1e03ea RM |
130 | |
131 | /* Set TF on the kernel stack.. */ | |
65ea5b03 | 132 | regs->flags |= X86_EFLAGS_TF; |
fa1e03ea RM |
133 | |
134 | /* | |
135 | * ..but if TF is changed by the instruction we will trace, | |
136 | * don't mark it as being "us" that set it, so that we | |
137 | * won't clear it by hand later. | |
6718d0d6 RM |
138 | * |
139 | * Note that if we don't actually execute the popf because | |
140 | * of a signal arriving right now or suchlike, we will lose | |
141 | * track of the fact that it really was "us" that set it. | |
fa1e03ea | 142 | */ |
6718d0d6 RM |
143 | if (is_setting_trap_flag(child, regs)) { |
144 | clear_tsk_thread_flag(child, TIF_FORCED_TF); | |
10faa81e | 145 | return 0; |
6718d0d6 RM |
146 | } |
147 | ||
148 | /* | |
149 | * If TF was already set, check whether it was us who set it. | |
150 | * If not, we should never attempt a block step. | |
151 | */ | |
152 | if (oflags & X86_EFLAGS_TF) | |
153 | return test_tsk_thread_flag(child, TIF_FORCED_TF); | |
fa1e03ea | 154 | |
e1f28773 | 155 | set_tsk_thread_flag(child, TIF_FORCED_TF); |
10faa81e RM |
156 | |
157 | return 1; | |
158 | } | |
159 | ||
160 | /* | |
161 | * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running. | |
162 | */ | |
163 | static void write_debugctlmsr(struct task_struct *child, unsigned long val) | |
164 | { | |
4ba51fd7 RM |
165 | if (child->thread.debugctlmsr == val) |
166 | return; | |
167 | ||
10faa81e RM |
168 | child->thread.debugctlmsr = val; |
169 | ||
170 | if (child != current) | |
171 | return; | |
172 | ||
5b0e5084 | 173 | update_debugctlmsr(val); |
10faa81e RM |
174 | } |
175 | ||
176 | /* | |
177 | * Enable single or block step. | |
178 | */ | |
179 | static void enable_step(struct task_struct *child, bool block) | |
180 | { | |
181 | /* | |
182 | * Make sure block stepping (BTF) is not enabled unless it should be. | |
183 | * Note that we don't try to worry about any is_setting_trap_flag() | |
184 | * instructions after the first when using block stepping. | |
185 | * So noone should try to use debugger block stepping in a program | |
186 | * that uses user-mode single stepping itself. | |
187 | */ | |
188 | if (enable_single_step(child) && block) { | |
189 | set_tsk_thread_flag(child, TIF_DEBUGCTLMSR); | |
eee3af4a MM |
190 | write_debugctlmsr(child, |
191 | child->thread.debugctlmsr | DEBUGCTLMSR_BTF); | |
192 | } else { | |
4ba51fd7 RM |
193 | write_debugctlmsr(child, |
194 | child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF); | |
eee3af4a | 195 | |
4ba51fd7 RM |
196 | if (!child->thread.debugctlmsr) |
197 | clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR); | |
10faa81e RM |
198 | } |
199 | } | |
200 | ||
201 | void user_enable_single_step(struct task_struct *child) | |
202 | { | |
203 | enable_step(child, 0); | |
204 | } | |
205 | ||
206 | void user_enable_block_step(struct task_struct *child) | |
207 | { | |
208 | enable_step(child, 1); | |
fa1e03ea RM |
209 | } |
210 | ||
211 | void user_disable_single_step(struct task_struct *child) | |
212 | { | |
10faa81e RM |
213 | /* |
214 | * Make sure block stepping (BTF) is disabled. | |
215 | */ | |
eee3af4a | 216 | write_debugctlmsr(child, |
d032b31a | 217 | child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF); |
eee3af4a MM |
218 | |
219 | if (!child->thread.debugctlmsr) | |
220 | clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR); | |
10faa81e | 221 | |
fa1e03ea RM |
222 | /* Always clear TIF_SINGLESTEP... */ |
223 | clear_tsk_thread_flag(child, TIF_SINGLESTEP); | |
224 | ||
225 | /* But touch TF only if it was set by us.. */ | |
e1f28773 | 226 | if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) |
65ea5b03 | 227 | task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; |
fa1e03ea | 228 | } |