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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> | |
154fcf3a | 9 | |
254e0a6b | 10 | #include <asm/desc.h> |
154fcf3a | 11 | #include <asm/debugreg.h> |
37868fe1 | 12 | #include <asm/mmu_context.h> |
fa1e03ea | 13 | |
37cd9cf3 | 14 | unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) |
fa1e03ea RM |
15 | { |
16 | unsigned long addr, seg; | |
17 | ||
65ea5b03 | 18 | addr = regs->ip; |
99504819 | 19 | seg = regs->cs; |
65ea5b03 | 20 | if (v8086_mode(regs)) { |
7122ec81 RM |
21 | addr = (addr & 0xffff) + (seg << 4); |
22 | return addr; | |
23 | } | |
fa1e03ea | 24 | |
a5b9e5a2 | 25 | #ifdef CONFIG_MODIFY_LDT_SYSCALL |
fa1e03ea RM |
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 | */ | |
3f80c1ad | 32 | if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { |
254e0a6b | 33 | struct desc_struct *desc; |
fa1e03ea RM |
34 | unsigned long base; |
35 | ||
136d9d83 | 36 | seg >>= 3; |
fa1e03ea RM |
37 | |
38 | mutex_lock(&child->mm->context.lock); | |
37868fe1 | 39 | if (unlikely(!child->mm->context.ldt || |
bbf79d21 | 40 | seg >= child->mm->context.ldt->nr_entries)) |
fa1e03ea RM |
41 | addr = -1L; /* bogus selector, access would fault */ |
42 | else { | |
37868fe1 | 43 | desc = &child->mm->context.ldt->entries[seg]; |
254e0a6b | 44 | base = get_desc_base(desc); |
fa1e03ea RM |
45 | |
46 | /* 16-bit code segment? */ | |
254e0a6b | 47 | if (!desc->d) |
fa1e03ea RM |
48 | addr &= 0xffff; |
49 | addr += base; | |
50 | } | |
51 | mutex_unlock(&child->mm->context.lock); | |
52 | } | |
a5b9e5a2 | 53 | #endif |
fa1e03ea RM |
54 | |
55 | return addr; | |
56 | } | |
57 | ||
58 | static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) | |
59 | { | |
60 | int i, copied; | |
61 | unsigned char opcode[15]; | |
37cd9cf3 | 62 | unsigned long addr = convert_ip_to_linear(child, regs); |
fa1e03ea | 63 | |
f307ab6d LS |
64 | copied = access_process_vm(child, addr, opcode, sizeof(opcode), |
65 | FOLL_FORCE); | |
fa1e03ea RM |
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: | |
5f76cb1f | 81 | case 0xf0: case 0xf2: case 0xf3: |
fa1e03ea RM |
82 | continue; |
83 | ||
7122ec81 | 84 | #ifdef CONFIG_X86_64 |
fa1e03ea | 85 | case 0x40 ... 0x4f: |
318f5a2a | 86 | if (!user_64bit_mode(regs)) |
fa1e03ea RM |
87 | /* 32-bit mode: register increment */ |
88 | return 0; | |
89 | /* 64-bit mode: REX prefix */ | |
90 | continue; | |
7122ec81 | 91 | #endif |
fa1e03ea RM |
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 | ||
10faa81e RM |
110 | /* |
111 | * Enable single-stepping. Return nonzero if user mode is not using TF itself. | |
112 | */ | |
113 | static int enable_single_step(struct task_struct *child) | |
fa1e03ea RM |
114 | { |
115 | struct pt_regs *regs = task_pt_regs(child); | |
6718d0d6 | 116 | unsigned long oflags; |
fa1e03ea | 117 | |
380fdd75 RM |
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 | ||
fa1e03ea | 131 | /* |
6342adca | 132 | * Always set TIF_SINGLESTEP. This will also |
fa1e03ea RM |
133 | * cause us to set TF when returning to user mode. |
134 | */ | |
135 | set_tsk_thread_flag(child, TIF_SINGLESTEP); | |
136 | ||
6342adca GKB |
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 | ||
6718d0d6 | 143 | oflags = regs->flags; |
fa1e03ea RM |
144 | |
145 | /* Set TF on the kernel stack.. */ | |
65ea5b03 | 146 | regs->flags |= X86_EFLAGS_TF; |
fa1e03ea RM |
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. | |
6718d0d6 RM |
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. | |
fa1e03ea | 156 | */ |
6718d0d6 RM |
157 | if (is_setting_trap_flag(child, regs)) { |
158 | clear_tsk_thread_flag(child, TIF_FORCED_TF); | |
10faa81e | 159 | return 0; |
6718d0d6 RM |
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); | |
fa1e03ea | 168 | |
e1f28773 | 169 | set_tsk_thread_flag(child, TIF_FORCED_TF); |
10faa81e RM |
170 | |
171 | return 1; | |
172 | } | |
173 | ||
9bd1190a | 174 | void set_task_blockstep(struct task_struct *task, bool on) |
848e8f5f ON |
175 | { |
176 | unsigned long debugctl; | |
177 | ||
95cf00fa ON |
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. | |
9899d11f ON |
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 | |
6a2d90ba | 185 | * with __switch_to_xtra(). We rely on ptrace_freeze_traced(). |
95cf00fa ON |
186 | */ |
187 | local_irq_disable(); | |
848e8f5f ON |
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 | } | |
95cf00fa ON |
196 | if (task == current) |
197 | update_debugctlmsr(debugctl); | |
198 | local_irq_enable(); | |
848e8f5f ON |
199 | } |
200 | ||
10faa81e RM |
201 | /* |
202 | * Enable single or block step. | |
203 | */ | |
204 | static 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. | |
0d2eb44f | 210 | * So no one should try to use debugger block stepping in a program |
10faa81e RM |
211 | * that uses user-mode single stepping itself. |
212 | */ | |
848e8f5f ON |
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); | |
10faa81e RM |
217 | } |
218 | ||
219 | void user_enable_single_step(struct task_struct *child) | |
220 | { | |
221 | enable_step(child, 0); | |
222 | } | |
223 | ||
224 | void user_enable_block_step(struct task_struct *child) | |
225 | { | |
226 | enable_step(child, 1); | |
fa1e03ea RM |
227 | } |
228 | ||
229 | void user_disable_single_step(struct task_struct *child) | |
230 | { | |
10faa81e RM |
231 | /* |
232 | * Make sure block stepping (BTF) is disabled. | |
233 | */ | |
848e8f5f ON |
234 | if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) |
235 | set_task_blockstep(child, false); | |
10faa81e | 236 | |
fa1e03ea RM |
237 | /* Always clear TIF_SINGLESTEP... */ |
238 | clear_tsk_thread_flag(child, TIF_SINGLESTEP); | |
6342adca | 239 | clear_task_syscall_work(child, SYSCALL_EXIT_TRAP); |
fa1e03ea RM |
240 | |
241 | /* But touch TF only if it was set by us.. */ | |
e1f28773 | 242 | if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) |
65ea5b03 | 243 | task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; |
fa1e03ea | 244 | } |