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 | |
14 | unsigned 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(lock: &child->mm->context.lock); |
52 | } |
53 | #endif |
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]; |
62 | unsigned long addr = convert_ip_to_linear(child, regs); |
63 | |
64 | copied = access_process_vm(tsk: child, addr, buf: opcode, len: sizeof(opcode), |
65 | gup_flags: 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 | */ |
113 | static 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(tsk: 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(tsk: 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(tsk: child, TIF_FORCED_TF); |
168 | |
169 | set_tsk_thread_flag(tsk: child, TIF_FORCED_TF); |
170 | |
171 | return 1; |
172 | } |
173 | |
174 | void 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(tsk: task, TIF_BLOCKSTEP); |
192 | } else { |
193 | debugctl &= ~DEBUGCTLMSR_BTF; |
194 | clear_tsk_thread_flag(tsk: task, TIF_BLOCKSTEP); |
195 | } |
196 | if (task == current) |
197 | update_debugctlmsr(debugctlmsr: debugctl); |
198 | local_irq_enable(); |
199 | } |
200 | |
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. |
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(task: child, on: true); |
215 | else if (test_tsk_thread_flag(tsk: child, TIF_BLOCKSTEP)) |
216 | set_task_blockstep(task: child, on: false); |
217 | } |
218 | |
219 | void user_enable_single_step(struct task_struct *child) |
220 | { |
221 | enable_step(child, block: 0); |
222 | } |
223 | |
224 | void user_enable_block_step(struct task_struct *child) |
225 | { |
226 | enable_step(child, block: 1); |
227 | } |
228 | |
229 | void 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(tsk: child, TIF_BLOCKSTEP)) |
235 | set_task_blockstep(task: child, on: false); |
236 | |
237 | /* Always clear TIF_SINGLESTEP... */ |
238 | clear_tsk_thread_flag(tsk: 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(tsk: child, TIF_FORCED_TF)) |
243 | task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; |
244 | } |
245 | |