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 | |
12 | unsigned 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(lock: &child->mm->context.lock); |
50 | } |
51 | #endif |
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]; |
60 | unsigned long addr = convert_ip_to_linear(child, regs); |
61 | |
62 | copied = access_process_vm(tsk: child, addr, buf: opcode, len: sizeof(opcode), |
63 | gup_flags: 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 | */ |
111 | static 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(tsk: 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(tsk: 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(tsk: child, TIF_FORCED_TF); |
166 | |
167 | set_tsk_thread_flag(tsk: child, TIF_FORCED_TF); |
168 | |
169 | return 1; |
170 | } |
171 | |
172 | void 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(tsk: task, TIF_BLOCKSTEP); |
190 | } else { |
191 | debugctl &= ~DEBUGCTLMSR_BTF; |
192 | clear_tsk_thread_flag(tsk: task, TIF_BLOCKSTEP); |
193 | } |
194 | if (task == current) |
195 | update_debugctlmsr(debugctlmsr: debugctl); |
196 | local_irq_enable(); |
197 | } |
198 | |
199 | /* |
200 | * Enable single or block step. |
201 | */ |
202 | static 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(task: child, on: true); |
213 | else if (test_tsk_thread_flag(tsk: child, TIF_BLOCKSTEP)) |
214 | set_task_blockstep(task: child, on: false); |
215 | } |
216 | |
217 | void user_enable_single_step(struct task_struct *child) |
218 | { |
219 | enable_step(child, block: 0); |
220 | } |
221 | |
222 | void user_enable_block_step(struct task_struct *child) |
223 | { |
224 | enable_step(child, block: 1); |
225 | } |
226 | |
227 | void 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(tsk: child, TIF_BLOCKSTEP)) |
233 | set_task_blockstep(task: child, on: false); |
234 | |
235 | /* Always clear TIF_SINGLESTEP... */ |
236 | clear_tsk_thread_flag(tsk: 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(tsk: child, TIF_FORCED_TF)) |
241 | task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; |
242 | } |
243 | |