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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>
37868fe1 8#include <asm/mmu_context.h>
fa1e03ea 9
37cd9cf3 10unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
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11{
12 unsigned long addr, seg;
13
65ea5b03 14 addr = regs->ip;
fa1e03ea 15 seg = regs->cs & 0xffff;
65ea5b03 16 if (v8086_mode(regs)) {
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17 addr = (addr & 0xffff) + (seg << 4);
18 return addr;
19 }
fa1e03ea 20
a5b9e5a2 21#ifdef CONFIG_MODIFY_LDT_SYSCALL
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22 /*
23 * We'll assume that the code segments in the GDT
24 * are all zero-based. That is largely true: the
25 * TLS segments are used for data, and the PNPBIOS
26 * and APM bios ones we just ignore here.
27 */
3f80c1ad 28 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
254e0a6b 29 struct desc_struct *desc;
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30 unsigned long base;
31
136d9d83 32 seg >>= 3;
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33
34 mutex_lock(&child->mm->context.lock);
37868fe1 35 if (unlikely(!child->mm->context.ldt ||
136d9d83 36 seg >= child->mm->context.ldt->size))
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37 addr = -1L; /* bogus selector, access would fault */
38 else {
37868fe1 39 desc = &child->mm->context.ldt->entries[seg];
254e0a6b 40 base = get_desc_base(desc);
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41
42 /* 16-bit code segment? */
254e0a6b 43 if (!desc->d)
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44 addr &= 0xffff;
45 addr += base;
46 }
47 mutex_unlock(&child->mm->context.lock);
48 }
a5b9e5a2 49#endif
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50
51 return addr;
52}
53
54static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
55{
56 int i, copied;
57 unsigned char opcode[15];
37cd9cf3 58 unsigned long addr = convert_ip_to_linear(child, regs);
fa1e03ea 59
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60 copied = access_process_vm(child, addr, opcode, sizeof(opcode),
61 FOLL_FORCE);
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62 for (i = 0; i < copied; i++) {
63 switch (opcode[i]) {
64 /* popf and iret */
65 case 0x9d: case 0xcf:
66 return 1;
67
68 /* CHECKME: 64 65 */
69
70 /* opcode and address size prefixes */
71 case 0x66: case 0x67:
72 continue;
73 /* irrelevant prefixes (segment overrides and repeats) */
74 case 0x26: case 0x2e:
75 case 0x36: case 0x3e:
76 case 0x64: case 0x65:
5f76cb1f 77 case 0xf0: case 0xf2: case 0xf3:
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78 continue;
79
7122ec81 80#ifdef CONFIG_X86_64
fa1e03ea 81 case 0x40 ... 0x4f:
318f5a2a 82 if (!user_64bit_mode(regs))
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83 /* 32-bit mode: register increment */
84 return 0;
85 /* 64-bit mode: REX prefix */
86 continue;
7122ec81 87#endif
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88
89 /* CHECKME: f2, f3 */
90
91 /*
92 * pushf: NOTE! We should probably not let
93 * the user see the TF bit being set. But
94 * it's more pain than it's worth to avoid
95 * it, and a debugger could emulate this
96 * all in user space if it _really_ cares.
97 */
98 case 0x9c:
99 default:
100 return 0;
101 }
102 }
103 return 0;
104}
105
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106/*
107 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
108 */
109static int enable_single_step(struct task_struct *child)
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110{
111 struct pt_regs *regs = task_pt_regs(child);
6718d0d6 112 unsigned long oflags;
fa1e03ea 113
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114 /*
115 * If we stepped into a sysenter/syscall insn, it trapped in
116 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
117 * If user-mode had set TF itself, then it's still clear from
118 * do_debug() and we need to set it again to restore the user
119 * state so we don't wrongly set TIF_FORCED_TF below.
120 * If enable_single_step() was used last and that is what
121 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
122 * already set and our bookkeeping is fine.
123 */
124 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
125 regs->flags |= X86_EFLAGS_TF;
126
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127 /*
128 * Always set TIF_SINGLESTEP - this guarantees that
129 * we single-step system calls etc.. This will also
130 * cause us to set TF when returning to user mode.
131 */
132 set_tsk_thread_flag(child, TIF_SINGLESTEP);
133
6718d0d6 134 oflags = regs->flags;
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135
136 /* Set TF on the kernel stack.. */
65ea5b03 137 regs->flags |= X86_EFLAGS_TF;
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138
139 /*
140 * ..but if TF is changed by the instruction we will trace,
141 * don't mark it as being "us" that set it, so that we
142 * won't clear it by hand later.
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143 *
144 * Note that if we don't actually execute the popf because
145 * of a signal arriving right now or suchlike, we will lose
146 * track of the fact that it really was "us" that set it.
fa1e03ea 147 */
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148 if (is_setting_trap_flag(child, regs)) {
149 clear_tsk_thread_flag(child, TIF_FORCED_TF);
10faa81e 150 return 0;
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151 }
152
153 /*
154 * If TF was already set, check whether it was us who set it.
155 * If not, we should never attempt a block step.
156 */
157 if (oflags & X86_EFLAGS_TF)
158 return test_tsk_thread_flag(child, TIF_FORCED_TF);
fa1e03ea 159
e1f28773 160 set_tsk_thread_flag(child, TIF_FORCED_TF);
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161
162 return 1;
163}
164
9bd1190a 165void set_task_blockstep(struct task_struct *task, bool on)
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166{
167 unsigned long debugctl;
168
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169 /*
170 * Ensure irq/preemption can't change debugctl in between.
171 * Note also that both TIF_BLOCKSTEP and debugctl should
172 * be changed atomically wrt preemption.
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173 *
174 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
175 * task is current or it can't be running, otherwise we can race
176 * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but
177 * PTRACE_KILL is not safe.
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178 */
179 local_irq_disable();
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180 debugctl = get_debugctlmsr();
181 if (on) {
182 debugctl |= DEBUGCTLMSR_BTF;
183 set_tsk_thread_flag(task, TIF_BLOCKSTEP);
184 } else {
185 debugctl &= ~DEBUGCTLMSR_BTF;
186 clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
187 }
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188 if (task == current)
189 update_debugctlmsr(debugctl);
190 local_irq_enable();
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191}
192
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193/*
194 * Enable single or block step.
195 */
196static void enable_step(struct task_struct *child, bool block)
197{
198 /*
199 * Make sure block stepping (BTF) is not enabled unless it should be.
200 * Note that we don't try to worry about any is_setting_trap_flag()
201 * instructions after the first when using block stepping.
0d2eb44f 202 * So no one should try to use debugger block stepping in a program
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203 * that uses user-mode single stepping itself.
204 */
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205 if (enable_single_step(child) && block)
206 set_task_blockstep(child, true);
207 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
208 set_task_blockstep(child, false);
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209}
210
211void user_enable_single_step(struct task_struct *child)
212{
213 enable_step(child, 0);
214}
215
216void user_enable_block_step(struct task_struct *child)
217{
218 enable_step(child, 1);
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219}
220
221void user_disable_single_step(struct task_struct *child)
222{
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223 /*
224 * Make sure block stepping (BTF) is disabled.
225 */
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226 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
227 set_task_blockstep(child, false);
10faa81e 228
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229 /* Always clear TIF_SINGLESTEP... */
230 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
231
232 /* But touch TF only if it was set by us.. */
e1f28773 233 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
65ea5b03 234 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
fa1e03ea 235}