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