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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * x86 single-step support code, common to 32-bit and 64-bit.
4 */
5#include <linux/sched.h>
6#include <linux/sched/task_stack.h>
7#include <linux/mm.h>
8#include <linux/ptrace.h>
9
10#include <asm/desc.h>
11#include <asm/debugreg.h>
12#include <asm/mmu_context.h>
13
14unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
15{
16 unsigned long addr, seg;
17
18 addr = regs->ip;
19 seg = regs->cs;
20 if (v8086_mode(regs)) {
21 addr = (addr & 0xffff) + (seg << 4);
22 return addr;
23 }
24
25#ifdef CONFIG_MODIFY_LDT_SYSCALL
26 /*
27 * We'll assume that the code segments in the GDT
28 * are all zero-based. That is largely true: the
29 * TLS segments are used for data, and the PNPBIOS
30 * and APM bios ones we just ignore here.
31 */
32 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
33 struct desc_struct *desc;
34 unsigned long base;
35
36 seg >>= 3;
37
38 mutex_lock(&child->mm->context.lock);
39 if (unlikely(!child->mm->context.ldt ||
40 seg >= child->mm->context.ldt->nr_entries))
41 addr = -1L; /* bogus selector, access would fault */
42 else {
43 desc = &child->mm->context.ldt->entries[seg];
44 base = get_desc_base(desc);
45
46 /* 16-bit code segment? */
47 if (!desc->d)
48 addr &= 0xffff;
49 addr += base;
50 }
51 mutex_unlock(&child->mm->context.lock);
52 }
53#endif
54
55 return addr;
56}
57
58static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
59{
60 int i, copied;
61 unsigned char opcode[15];
62 unsigned long addr = convert_ip_to_linear(child, regs);
63
64 copied = access_process_vm(child, addr, opcode, sizeof(opcode),
65 FOLL_FORCE);
66 for (i = 0; i < copied; i++) {
67 switch (opcode[i]) {
68 /* popf and iret */
69 case 0x9d: case 0xcf:
70 return 1;
71
72 /* CHECKME: 64 65 */
73
74 /* opcode and address size prefixes */
75 case 0x66: case 0x67:
76 continue;
77 /* irrelevant prefixes (segment overrides and repeats) */
78 case 0x26: case 0x2e:
79 case 0x36: case 0x3e:
80 case 0x64: case 0x65:
81 case 0xf0: case 0xf2: case 0xf3:
82 continue;
83
84#ifdef CONFIG_X86_64
85 case 0x40 ... 0x4f:
86 if (!user_64bit_mode(regs))
87 /* 32-bit mode: register increment */
88 return 0;
89 /* 64-bit mode: REX prefix */
90 continue;
91#endif
92
93 /* CHECKME: f2, f3 */
94
95 /*
96 * pushf: NOTE! We should probably not let
97 * the user see the TF bit being set. But
98 * it's more pain than it's worth to avoid
99 * it, and a debugger could emulate this
100 * all in user space if it _really_ cares.
101 */
102 case 0x9c:
103 default:
104 return 0;
105 }
106 }
107 return 0;
108}
109
110/*
111 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
112 */
113static int enable_single_step(struct task_struct *child)
114{
115 struct pt_regs *regs = task_pt_regs(child);
116 unsigned long oflags;
117
118 /*
119 * If we stepped into a sysenter/syscall insn, it trapped in
120 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
121 * If user-mode had set TF itself, then it's still clear from
122 * do_debug() and we need to set it again to restore the user
123 * state so we don't wrongly set TIF_FORCED_TF below.
124 * If enable_single_step() was used last and that is what
125 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
126 * already set and our bookkeeping is fine.
127 */
128 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
129 regs->flags |= X86_EFLAGS_TF;
130
131 /*
132 * Always set TIF_SINGLESTEP. This will also
133 * cause us to set TF when returning to user mode.
134 */
135 set_tsk_thread_flag(child, TIF_SINGLESTEP);
136
137 /*
138 * Ensure that a trap is triggered once stepping out of a system
139 * call prior to executing any user instruction.
140 */
141 set_task_syscall_work(child, SYSCALL_EXIT_TRAP);
142
143 oflags = regs->flags;
144
145 /* Set TF on the kernel stack.. */
146 regs->flags |= X86_EFLAGS_TF;
147
148 /*
149 * ..but if TF is changed by the instruction we will trace,
150 * don't mark it as being "us" that set it, so that we
151 * won't clear it by hand later.
152 *
153 * Note that if we don't actually execute the popf because
154 * of a signal arriving right now or suchlike, we will lose
155 * track of the fact that it really was "us" that set it.
156 */
157 if (is_setting_trap_flag(child, regs)) {
158 clear_tsk_thread_flag(child, TIF_FORCED_TF);
159 return 0;
160 }
161
162 /*
163 * If TF was already set, check whether it was us who set it.
164 * If not, we should never attempt a block step.
165 */
166 if (oflags & X86_EFLAGS_TF)
167 return test_tsk_thread_flag(child, TIF_FORCED_TF);
168
169 set_tsk_thread_flag(child, TIF_FORCED_TF);
170
171 return 1;
172}
173
174void set_task_blockstep(struct task_struct *task, bool on)
175{
176 unsigned long debugctl;
177
178 /*
179 * Ensure irq/preemption can't change debugctl in between.
180 * Note also that both TIF_BLOCKSTEP and debugctl should
181 * be changed atomically wrt preemption.
182 *
183 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
184 * task is current or it can't be running, otherwise we can race
185 * with __switch_to_xtra(). We rely on ptrace_freeze_traced().
186 */
187 local_irq_disable();
188 debugctl = get_debugctlmsr();
189 if (on) {
190 debugctl |= DEBUGCTLMSR_BTF;
191 set_tsk_thread_flag(task, TIF_BLOCKSTEP);
192 } else {
193 debugctl &= ~DEBUGCTLMSR_BTF;
194 clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
195 }
196 if (task == current)
197 update_debugctlmsr(debugctl);
198 local_irq_enable();
199}
200
201/*
202 * Enable single or block step.
203 */
204static void enable_step(struct task_struct *child, bool block)
205{
206 /*
207 * Make sure block stepping (BTF) is not enabled unless it should be.
208 * Note that we don't try to worry about any is_setting_trap_flag()
209 * instructions after the first when using block stepping.
210 * So no one should try to use debugger block stepping in a program
211 * that uses user-mode single stepping itself.
212 */
213 if (enable_single_step(child) && block)
214 set_task_blockstep(child, true);
215 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
216 set_task_blockstep(child, false);
217}
218
219void user_enable_single_step(struct task_struct *child)
220{
221 enable_step(child, 0);
222}
223
224void user_enable_block_step(struct task_struct *child)
225{
226 enable_step(child, 1);
227}
228
229void user_disable_single_step(struct task_struct *child)
230{
231 /*
232 * Make sure block stepping (BTF) is disabled.
233 */
234 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
235 set_task_blockstep(child, false);
236
237 /* Always clear TIF_SINGLESTEP... */
238 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
239 clear_task_syscall_work(child, SYSCALL_EXIT_TRAP);
240
241 /* But touch TF only if it was set by us.. */
242 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
243 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
244}
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#include <asm/mmu_context.h>
9
10unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
11{
12 unsigned long addr, seg;
13
14 addr = regs->ip;
15 seg = regs->cs & 0xffff;
16 if (v8086_mode(regs)) {
17 addr = (addr & 0xffff) + (seg << 4);
18 return addr;
19 }
20
21#ifdef CONFIG_MODIFY_LDT_SYSCALL
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 */
28 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
29 struct desc_struct *desc;
30 unsigned long base;
31
32 seg >>= 3;
33
34 mutex_lock(&child->mm->context.lock);
35 if (unlikely(!child->mm->context.ldt ||
36 seg >= child->mm->context.ldt->size))
37 addr = -1L; /* bogus selector, access would fault */
38 else {
39 desc = &child->mm->context.ldt->entries[seg];
40 base = get_desc_base(desc);
41
42 /* 16-bit code segment? */
43 if (!desc->d)
44 addr &= 0xffff;
45 addr += base;
46 }
47 mutex_unlock(&child->mm->context.lock);
48 }
49#endif
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];
58 unsigned long addr = convert_ip_to_linear(child, regs);
59
60 copied = access_process_vm(child, addr, opcode, sizeof(opcode),
61 FOLL_FORCE);
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:
77 case 0xf0: case 0xf2: case 0xf3:
78 continue;
79
80#ifdef CONFIG_X86_64
81 case 0x40 ... 0x4f:
82 if (!user_64bit_mode(regs))
83 /* 32-bit mode: register increment */
84 return 0;
85 /* 64-bit mode: REX prefix */
86 continue;
87#endif
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
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)
110{
111 struct pt_regs *regs = task_pt_regs(child);
112 unsigned long oflags;
113
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
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
134 oflags = regs->flags;
135
136 /* Set TF on the kernel stack.. */
137 regs->flags |= X86_EFLAGS_TF;
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.
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.
147 */
148 if (is_setting_trap_flag(child, regs)) {
149 clear_tsk_thread_flag(child, TIF_FORCED_TF);
150 return 0;
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);
159
160 set_tsk_thread_flag(child, TIF_FORCED_TF);
161
162 return 1;
163}
164
165void set_task_blockstep(struct task_struct *task, bool on)
166{
167 unsigned long debugctl;
168
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.
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.
178 */
179 local_irq_disable();
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 }
188 if (task == current)
189 update_debugctlmsr(debugctl);
190 local_irq_enable();
191}
192
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.
202 * So no one should try to use debugger block stepping in a program
203 * that uses user-mode single stepping itself.
204 */
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);
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);
219}
220
221void user_disable_single_step(struct task_struct *child)
222{
223 /*
224 * Make sure block stepping (BTF) is disabled.
225 */
226 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
227 set_task_blockstep(child, false);
228
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.. */
233 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
234 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
235}