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>
7
8 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
9 {
10 unsigned long addr, seg;
11
12 addr = regs->ip;
13 seg = regs->cs & 0xffff;
14 if (v8086_mode(regs)) {
15 addr = (addr & 0xffff) + (seg << 4);
16 return addr;
17 }
18
19 /*
20 * We'll assume that the code segments in the GDT
21 * are all zero-based. That is largely true: the
22 * TLS segments are used for data, and the PNPBIOS
23 * and APM bios ones we just ignore here.
24 */
25 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
26 u32 *desc;
27 unsigned long base;
28
29 seg &= ~7UL;
30
31 mutex_lock(&child->mm->context.lock);
32 if (unlikely((seg >> 3) >= child->mm->context.size))
33 addr = -1L; /* bogus selector, access would fault */
34 else {
35 desc = child->mm->context.ldt + seg;
36 base = ((desc[0] >> 16) |
37 ((desc[1] & 0xff) << 16) |
38 (desc[1] & 0xff000000));
39
40 /* 16-bit code segment? */
41 if (!((desc[1] >> 22) & 1))
42 addr &= 0xffff;
43 addr += base;
44 }
45 mutex_unlock(&child->mm->context.lock);
46 }
47
48 return addr;
49 }
50
51 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
52 {
53 int i, copied;
54 unsigned char opcode[15];
55 unsigned long addr = convert_ip_to_linear(child, regs);
56
57 copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
58 for (i = 0; i < copied; i++) {
59 switch (opcode[i]) {
60 /* popf and iret */
61 case 0x9d: case 0xcf:
62 return 1;
63
64 /* CHECKME: 64 65 */
65
66 /* opcode and address size prefixes */
67 case 0x66: case 0x67:
68 continue;
69 /* irrelevant prefixes (segment overrides and repeats) */
70 case 0x26: case 0x2e:
71 case 0x36: case 0x3e:
72 case 0x64: case 0x65:
73 case 0xf0: case 0xf2: case 0xf3:
74 continue;
75
76 #ifdef CONFIG_X86_64
77 case 0x40 ... 0x4f:
78 if (regs->cs != __USER_CS)
79 /* 32-bit mode: register increment */
80 return 0;
81 /* 64-bit mode: REX prefix */
82 continue;
83 #endif
84
85 /* CHECKME: f2, f3 */
86
87 /*
88 * pushf: NOTE! We should probably not let
89 * the user see the TF bit being set. But
90 * it's more pain than it's worth to avoid
91 * it, and a debugger could emulate this
92 * all in user space if it _really_ cares.
93 */
94 case 0x9c:
95 default:
96 return 0;
97 }
98 }
99 return 0;
100 }
101
102 /*
103 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
104 */
105 static int enable_single_step(struct task_struct *child)
106 {
107 struct pt_regs *regs = task_pt_regs(child);
108
109 /*
110 * Always set TIF_SINGLESTEP - this guarantees that
111 * we single-step system calls etc.. This will also
112 * cause us to set TF when returning to user mode.
113 */
114 set_tsk_thread_flag(child, TIF_SINGLESTEP);
115
116 /*
117 * If TF was already set, don't do anything else
118 */
119 if (regs->flags & X86_EFLAGS_TF)
120 return 0;
121
122 /* Set TF on the kernel stack.. */
123 regs->flags |= X86_EFLAGS_TF;
124
125 /*
126 * ..but if TF is changed by the instruction we will trace,
127 * don't mark it as being "us" that set it, so that we
128 * won't clear it by hand later.
129 */
130 if (is_setting_trap_flag(child, regs))
131 return 0;
132
133 set_tsk_thread_flag(child, TIF_FORCED_TF);
134
135 return 1;
136 }
137
138 /*
139 * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running.
140 */
141 static void write_debugctlmsr(struct task_struct *child, unsigned long val)
142 {
143 if (child->thread.debugctlmsr == val)
144 return;
145
146 child->thread.debugctlmsr = val;
147
148 if (child != current)
149 return;
150
151 wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
152 }
153
154 /*
155 * Enable single or block step.
156 */
157 static void enable_step(struct task_struct *child, bool block)
158 {
159 /*
160 * Make sure block stepping (BTF) is not enabled unless it should be.
161 * Note that we don't try to worry about any is_setting_trap_flag()
162 * instructions after the first when using block stepping.
163 * So noone should try to use debugger block stepping in a program
164 * that uses user-mode single stepping itself.
165 */
166 if (enable_single_step(child) && block) {
167 set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
168 write_debugctlmsr(child,
169 child->thread.debugctlmsr | DEBUGCTLMSR_BTF);
170 } else {
171 write_debugctlmsr(child,
172 child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
173
174 if (!child->thread.debugctlmsr)
175 clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
176 }
177 }
178
179 void user_enable_single_step(struct task_struct *child)
180 {
181 enable_step(child, 0);
182 }
183
184 void user_enable_block_step(struct task_struct *child)
185 {
186 enable_step(child, 1);
187 }
188
189 void user_disable_single_step(struct task_struct *child)
190 {
191 /*
192 * Make sure block stepping (BTF) is disabled.
193 */
194 write_debugctlmsr(child,
195 child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
196
197 if (!child->thread.debugctlmsr)
198 clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
199
200 /* Always clear TIF_SINGLESTEP... */
201 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
202
203 /* But touch TF only if it was set by us.. */
204 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
205 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
206 }
207
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