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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
fa1e03ea RM |
2 | /* |
3 | * x86 single-step support code, common to 32-bit and 64-bit. | |
4 | */ | |
5 | #include <linux/sched.h> | |
68db0cf1 | 6 | #include <linux/sched/task_stack.h> |
fa1e03ea RM |
7 | #include <linux/mm.h> |
8 | #include <linux/ptrace.h> | |
254e0a6b | 9 | #include <asm/desc.h> |
37868fe1 | 10 | #include <asm/mmu_context.h> |
fa1e03ea | 11 | |
37cd9cf3 | 12 | unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) |
fa1e03ea RM |
13 | { |
14 | unsigned long addr, seg; | |
15 | ||
65ea5b03 | 16 | addr = regs->ip; |
99504819 | 17 | seg = regs->cs; |
65ea5b03 | 18 | if (v8086_mode(regs)) { |
7122ec81 RM |
19 | addr = (addr & 0xffff) + (seg << 4); |
20 | return addr; | |
21 | } | |
fa1e03ea | 22 | |
a5b9e5a2 | 23 | #ifdef CONFIG_MODIFY_LDT_SYSCALL |
fa1e03ea RM |
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 | */ | |
3f80c1ad | 30 | if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { |
254e0a6b | 31 | struct desc_struct *desc; |
fa1e03ea RM |
32 | unsigned long base; |
33 | ||
136d9d83 | 34 | seg >>= 3; |
fa1e03ea RM |
35 | |
36 | mutex_lock(&child->mm->context.lock); | |
37868fe1 | 37 | if (unlikely(!child->mm->context.ldt || |
bbf79d21 | 38 | seg >= child->mm->context.ldt->nr_entries)) |
fa1e03ea RM |
39 | addr = -1L; /* bogus selector, access would fault */ |
40 | else { | |
37868fe1 | 41 | desc = &child->mm->context.ldt->entries[seg]; |
254e0a6b | 42 | base = get_desc_base(desc); |
fa1e03ea RM |
43 | |
44 | /* 16-bit code segment? */ | |
254e0a6b | 45 | if (!desc->d) |
fa1e03ea RM |
46 | addr &= 0xffff; |
47 | addr += base; | |
48 | } | |
49 | mutex_unlock(&child->mm->context.lock); | |
50 | } | |
a5b9e5a2 | 51 | #endif |
fa1e03ea RM |
52 | |
53 | return addr; | |
54 | } | |
55 | ||
56 | static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) | |
57 | { | |
58 | int i, copied; | |
59 | unsigned char opcode[15]; | |
37cd9cf3 | 60 | unsigned long addr = convert_ip_to_linear(child, regs); |
fa1e03ea | 61 | |
f307ab6d LS |
62 | copied = access_process_vm(child, addr, opcode, sizeof(opcode), |
63 | FOLL_FORCE); | |
fa1e03ea RM |
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: | |
5f76cb1f | 79 | case 0xf0: case 0xf2: case 0xf3: |
fa1e03ea RM |
80 | continue; |
81 | ||
7122ec81 | 82 | #ifdef CONFIG_X86_64 |
fa1e03ea | 83 | case 0x40 ... 0x4f: |
318f5a2a | 84 | if (!user_64bit_mode(regs)) |
fa1e03ea RM |
85 | /* 32-bit mode: register increment */ |
86 | return 0; | |
87 | /* 64-bit mode: REX prefix */ | |
88 | continue; | |
7122ec81 | 89 | #endif |
fa1e03ea RM |
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 | ||
10faa81e RM |
108 | /* |
109 | * Enable single-stepping. Return nonzero if user mode is not using TF itself. | |
110 | */ | |
111 | static int enable_single_step(struct task_struct *child) | |
fa1e03ea RM |
112 | { |
113 | struct pt_regs *regs = task_pt_regs(child); | |
6718d0d6 | 114 | unsigned long oflags; |
fa1e03ea | 115 | |
380fdd75 RM |
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 | ||
fa1e03ea RM |
129 | /* |
130 | * Always set TIF_SINGLESTEP - this guarantees that | |
131 | * we single-step system calls etc.. This will also | |
132 | * cause us to set TF when returning to user mode. | |
133 | */ | |
134 | set_tsk_thread_flag(child, TIF_SINGLESTEP); | |
135 | ||
6718d0d6 | 136 | oflags = regs->flags; |
fa1e03ea RM |
137 | |
138 | /* Set TF on the kernel stack.. */ | |
65ea5b03 | 139 | regs->flags |= X86_EFLAGS_TF; |
fa1e03ea RM |
140 | |
141 | /* | |
142 | * ..but if TF is changed by the instruction we will trace, | |
143 | * don't mark it as being "us" that set it, so that we | |
144 | * won't clear it by hand later. | |
6718d0d6 RM |
145 | * |
146 | * Note that if we don't actually execute the popf because | |
147 | * of a signal arriving right now or suchlike, we will lose | |
148 | * track of the fact that it really was "us" that set it. | |
fa1e03ea | 149 | */ |
6718d0d6 RM |
150 | if (is_setting_trap_flag(child, regs)) { |
151 | clear_tsk_thread_flag(child, TIF_FORCED_TF); | |
10faa81e | 152 | return 0; |
6718d0d6 RM |
153 | } |
154 | ||
155 | /* | |
156 | * If TF was already set, check whether it was us who set it. | |
157 | * If not, we should never attempt a block step. | |
158 | */ | |
159 | if (oflags & X86_EFLAGS_TF) | |
160 | return test_tsk_thread_flag(child, TIF_FORCED_TF); | |
fa1e03ea | 161 | |
e1f28773 | 162 | set_tsk_thread_flag(child, TIF_FORCED_TF); |
10faa81e RM |
163 | |
164 | return 1; | |
165 | } | |
166 | ||
9bd1190a | 167 | void set_task_blockstep(struct task_struct *task, bool on) |
848e8f5f ON |
168 | { |
169 | unsigned long debugctl; | |
170 | ||
95cf00fa ON |
171 | /* |
172 | * Ensure irq/preemption can't change debugctl in between. | |
173 | * Note also that both TIF_BLOCKSTEP and debugctl should | |
174 | * be changed atomically wrt preemption. | |
9899d11f ON |
175 | * |
176 | * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if | |
177 | * task is current or it can't be running, otherwise we can race | |
178 | * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but | |
179 | * PTRACE_KILL is not safe. | |
95cf00fa ON |
180 | */ |
181 | local_irq_disable(); | |
848e8f5f ON |
182 | debugctl = get_debugctlmsr(); |
183 | if (on) { | |
184 | debugctl |= DEBUGCTLMSR_BTF; | |
185 | set_tsk_thread_flag(task, TIF_BLOCKSTEP); | |
186 | } else { | |
187 | debugctl &= ~DEBUGCTLMSR_BTF; | |
188 | clear_tsk_thread_flag(task, TIF_BLOCKSTEP); | |
189 | } | |
95cf00fa ON |
190 | if (task == current) |
191 | update_debugctlmsr(debugctl); | |
192 | local_irq_enable(); | |
848e8f5f ON |
193 | } |
194 | ||
10faa81e RM |
195 | /* |
196 | * Enable single or block step. | |
197 | */ | |
198 | static void enable_step(struct task_struct *child, bool block) | |
199 | { | |
200 | /* | |
201 | * Make sure block stepping (BTF) is not enabled unless it should be. | |
202 | * Note that we don't try to worry about any is_setting_trap_flag() | |
203 | * instructions after the first when using block stepping. | |
0d2eb44f | 204 | * So no one should try to use debugger block stepping in a program |
10faa81e RM |
205 | * that uses user-mode single stepping itself. |
206 | */ | |
848e8f5f ON |
207 | if (enable_single_step(child) && block) |
208 | set_task_blockstep(child, true); | |
209 | else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) | |
210 | set_task_blockstep(child, false); | |
10faa81e RM |
211 | } |
212 | ||
213 | void user_enable_single_step(struct task_struct *child) | |
214 | { | |
215 | enable_step(child, 0); | |
216 | } | |
217 | ||
218 | void user_enable_block_step(struct task_struct *child) | |
219 | { | |
220 | enable_step(child, 1); | |
fa1e03ea RM |
221 | } |
222 | ||
223 | void user_disable_single_step(struct task_struct *child) | |
224 | { | |
10faa81e RM |
225 | /* |
226 | * Make sure block stepping (BTF) is disabled. | |
227 | */ | |
848e8f5f ON |
228 | if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) |
229 | set_task_blockstep(child, false); | |
10faa81e | 230 | |
fa1e03ea RM |
231 | /* Always clear TIF_SINGLESTEP... */ |
232 | clear_tsk_thread_flag(child, TIF_SINGLESTEP); | |
233 | ||
234 | /* But touch TF only if it was set by us.. */ | |
e1f28773 | 235 | if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) |
65ea5b03 | 236 | task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; |
fa1e03ea | 237 | } |