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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>
7#include <asm/desc.h>
8
9unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
10{
11 unsigned long addr, seg;
12
13 addr = regs->ip;
14 seg = regs->cs & 0xffff;
15 if (v8086_mode(regs)) {
16 addr = (addr & 0xffff) + (seg << 4);
17 return addr;
18 }
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 */
26 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
27 struct desc_struct *desc;
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;
37 base = get_desc_base(desc);
38
39 /* 16-bit code segment? */
40 if (!desc->d)
41 addr &= 0xffff;
42 addr += base;
43 }
44 mutex_unlock(&child->mm->context.lock);
45 }
46
47 return addr;
48}
49
50static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
51{
52 int i, copied;
53 unsigned char opcode[15];
54 unsigned long addr = convert_ip_to_linear(child, regs);
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:
72 case 0xf0: case 0xf2: case 0xf3:
73 continue;
74
75#ifdef CONFIG_X86_64
76 case 0x40 ... 0x4f:
77 if (!user_64bit_mode(regs))
78 /* 32-bit mode: register increment */
79 return 0;
80 /* 64-bit mode: REX prefix */
81 continue;
82#endif
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
101/*
102 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
103 */
104static int enable_single_step(struct task_struct *child)
105{
106 struct pt_regs *regs = task_pt_regs(child);
107 unsigned long oflags;
108
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
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
129 oflags = regs->flags;
130
131 /* Set TF on the kernel stack.. */
132 regs->flags |= X86_EFLAGS_TF;
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.
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.
142 */
143 if (is_setting_trap_flag(child, regs)) {
144 clear_tsk_thread_flag(child, TIF_FORCED_TF);
145 return 0;
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);
154
155 set_tsk_thread_flag(child, TIF_FORCED_TF);
156
157 return 1;
158}
159
160/*
161 * Enable single or block step.
162 */
163static void enable_step(struct task_struct *child, bool block)
164{
165 /*
166 * Make sure block stepping (BTF) is not enabled unless it should be.
167 * Note that we don't try to worry about any is_setting_trap_flag()
168 * instructions after the first when using block stepping.
169 * So no one should try to use debugger block stepping in a program
170 * that uses user-mode single stepping itself.
171 */
172 if (enable_single_step(child) && block) {
173 unsigned long debugctl = get_debugctlmsr();
174
175 debugctl |= DEBUGCTLMSR_BTF;
176 update_debugctlmsr(debugctl);
177 set_tsk_thread_flag(child, TIF_BLOCKSTEP);
178 } else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
179 unsigned long debugctl = get_debugctlmsr();
180
181 debugctl &= ~DEBUGCTLMSR_BTF;
182 update_debugctlmsr(debugctl);
183 clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
184 }
185}
186
187void user_enable_single_step(struct task_struct *child)
188{
189 enable_step(child, 0);
190}
191
192void user_enable_block_step(struct task_struct *child)
193{
194 enable_step(child, 1);
195}
196
197void user_disable_single_step(struct task_struct *child)
198{
199 /*
200 * Make sure block stepping (BTF) is disabled.
201 */
202 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
203 unsigned long debugctl = get_debugctlmsr();
204
205 debugctl &= ~DEBUGCTLMSR_BTF;
206 update_debugctlmsr(debugctl);
207 clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
208 }
209
210 /* Always clear TIF_SINGLESTEP... */
211 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
212
213 /* But touch TF only if it was set by us.. */
214 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
215 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
216}
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#include <asm/desc.h>
8
9unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
10{
11 unsigned long addr, seg;
12
13 addr = regs->ip;
14 seg = regs->cs & 0xffff;
15 if (v8086_mode(regs)) {
16 addr = (addr & 0xffff) + (seg << 4);
17 return addr;
18 }
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 */
26 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
27 struct desc_struct *desc;
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;
37 base = get_desc_base(desc);
38
39 /* 16-bit code segment? */
40 if (!desc->d)
41 addr &= 0xffff;
42 addr += base;
43 }
44 mutex_unlock(&child->mm->context.lock);
45 }
46
47 return addr;
48}
49
50static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
51{
52 int i, copied;
53 unsigned char opcode[15];
54 unsigned long addr = convert_ip_to_linear(child, regs);
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:
72 case 0xf0: case 0xf2: case 0xf3:
73 continue;
74
75#ifdef CONFIG_X86_64
76 case 0x40 ... 0x4f:
77 if (!user_64bit_mode(regs))
78 /* 32-bit mode: register increment */
79 return 0;
80 /* 64-bit mode: REX prefix */
81 continue;
82#endif
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
101/*
102 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
103 */
104static int enable_single_step(struct task_struct *child)
105{
106 struct pt_regs *regs = task_pt_regs(child);
107 unsigned long oflags;
108
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
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
129 oflags = regs->flags;
130
131 /* Set TF on the kernel stack.. */
132 regs->flags |= X86_EFLAGS_TF;
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.
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.
142 */
143 if (is_setting_trap_flag(child, regs)) {
144 clear_tsk_thread_flag(child, TIF_FORCED_TF);
145 return 0;
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);
154
155 set_tsk_thread_flag(child, TIF_FORCED_TF);
156
157 return 1;
158}
159
160void set_task_blockstep(struct task_struct *task, bool on)
161{
162 unsigned long debugctl;
163
164 /*
165 * Ensure irq/preemption can't change debugctl in between.
166 * Note also that both TIF_BLOCKSTEP and debugctl should
167 * be changed atomically wrt preemption.
168 *
169 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
170 * task is current or it can't be running, otherwise we can race
171 * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but
172 * PTRACE_KILL is not safe.
173 */
174 local_irq_disable();
175 debugctl = get_debugctlmsr();
176 if (on) {
177 debugctl |= DEBUGCTLMSR_BTF;
178 set_tsk_thread_flag(task, TIF_BLOCKSTEP);
179 } else {
180 debugctl &= ~DEBUGCTLMSR_BTF;
181 clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
182 }
183 if (task == current)
184 update_debugctlmsr(debugctl);
185 local_irq_enable();
186}
187
188/*
189 * Enable single or block step.
190 */
191static void enable_step(struct task_struct *child, bool block)
192{
193 /*
194 * Make sure block stepping (BTF) is not enabled unless it should be.
195 * Note that we don't try to worry about any is_setting_trap_flag()
196 * instructions after the first when using block stepping.
197 * So no one should try to use debugger block stepping in a program
198 * that uses user-mode single stepping itself.
199 */
200 if (enable_single_step(child) && block)
201 set_task_blockstep(child, true);
202 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
203 set_task_blockstep(child, false);
204}
205
206void user_enable_single_step(struct task_struct *child)
207{
208 enable_step(child, 0);
209}
210
211void user_enable_block_step(struct task_struct *child)
212{
213 enable_step(child, 1);
214}
215
216void user_disable_single_step(struct task_struct *child)
217{
218 /*
219 * Make sure block stepping (BTF) is disabled.
220 */
221 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
222 set_task_blockstep(child, false);
223
224 /* Always clear TIF_SINGLESTEP... */
225 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
226
227 /* But touch TF only if it was set by us.. */
228 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
229 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
230}