Branch data Line data Source code
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 : 0 : unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
13 : : {
14 : 0 : unsigned long addr, seg;
15 : :
16 : 0 : addr = regs->ip;
17 : 0 : seg = regs->cs;
18 [ # # ]: 0 : 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 [ # # ]: 0 : if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
31 : 0 : struct desc_struct *desc;
32 : 0 : unsigned long base;
33 : :
34 : 0 : seg >>= 3;
35 : :
36 : 0 : mutex_lock(&child->mm->context.lock);
37 [ # # # # ]: 0 : 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 : 0 : desc = &child->mm->context.ldt->entries[seg];
42 [ # # ]: 0 : base = get_desc_base(desc);
43 : :
44 : : /* 16-bit code segment? */
45 [ # # ]: 0 : if (!desc->d)
46 : 0 : addr &= 0xffff;
47 : 0 : addr += base;
48 : : }
49 : 0 : mutex_unlock(&child->mm->context.lock);
50 : : }
51 : : #endif
52 : :
53 : 0 : return addr;
54 : : }
55 : :
56 : 0 : static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
57 : : {
58 : 0 : int i, copied;
59 : 0 : unsigned char opcode[15];
60 : 0 : unsigned long addr = convert_ip_to_linear(child, regs);
61 : :
62 : 0 : copied = access_process_vm(child, addr, opcode, sizeof(opcode),
63 : : FOLL_FORCE);
64 [ # # ]: 0 : for (i = 0; i < copied; i++) {
65 [ # # # # : 0 : 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 : 0 : case 0x66: case 0x67:
74 : 0 : continue;
75 : : /* irrelevant prefixes (segment overrides and repeats) */
76 : 0 : case 0x26: case 0x2e:
77 : : case 0x36: case 0x3e:
78 : : case 0x64: case 0x65:
79 : : case 0xf0: case 0xf2: case 0xf3:
80 : 0 : continue;
81 : :
82 : : #ifdef CONFIG_X86_64
83 : 0 : case 0x40 ... 0x4f:
84 [ # # ]: 0 : if (!user_64bit_mode(regs))
85 : : /* 32-bit mode: register increment */
86 : : return 0;
87 : : /* 64-bit mode: REX prefix */
88 : 0 : 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 : 0 : case 0x9c:
101 : : default:
102 : 0 : 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 : 0 : static int enable_single_step(struct task_struct *child)
112 : : {
113 : 0 : struct pt_regs *regs = task_pt_regs(child);
114 : 0 : 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 [ # # ]: 0 : if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
127 : 0 : regs->flags |= X86_EFLAGS_TF;
128 : :
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 : 0 : set_tsk_thread_flag(child, TIF_SINGLESTEP);
135 : :
136 : 0 : oflags = regs->flags;
137 : :
138 : : /* Set TF on the kernel stack.. */
139 : 0 : regs->flags |= X86_EFLAGS_TF;
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.
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.
149 : : */
150 [ # # ]: 0 : if (is_setting_trap_flag(child, regs)) {
151 : 0 : clear_tsk_thread_flag(child, TIF_FORCED_TF);
152 : 0 : return 0;
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 [ # # ]: 0 : if (oflags & X86_EFLAGS_TF)
160 : 0 : return test_tsk_thread_flag(child, TIF_FORCED_TF);
161 : :
162 : 0 : set_tsk_thread_flag(child, TIF_FORCED_TF);
163 : :
164 : 0 : return 1;
165 : : }
166 : :
167 : 0 : void set_task_blockstep(struct task_struct *task, bool on)
168 : : {
169 : 0 : unsigned long debugctl;
170 : :
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.
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.
180 : : */
181 : 0 : local_irq_disable();
182 : 0 : debugctl = get_debugctlmsr();
183 [ # # ]: 0 : if (on) {
184 : 0 : debugctl |= DEBUGCTLMSR_BTF;
185 : 0 : set_tsk_thread_flag(task, TIF_BLOCKSTEP);
186 : : } else {
187 : 0 : debugctl &= ~DEBUGCTLMSR_BTF;
188 : 0 : clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
189 : : }
190 [ # # ]: 0 : if (task == current)
191 : 0 : update_debugctlmsr(debugctl);
192 : 0 : local_irq_enable();
193 : 0 : }
194 : :
195 : : /*
196 : : * Enable single or block step.
197 : : */
198 : 0 : 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.
204 : : * So no one should try to use debugger block stepping in a program
205 : : * that uses user-mode single stepping itself.
206 : : */
207 [ # # # # ]: 0 : if (enable_single_step(child) && block)
208 : 0 : set_task_blockstep(child, true);
209 [ # # ]: 0 : else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
210 : 0 : set_task_blockstep(child, false);
211 : 0 : }
212 : :
213 : 0 : void user_enable_single_step(struct task_struct *child)
214 : : {
215 : 0 : enable_step(child, 0);
216 : 0 : }
217 : :
218 : 0 : void user_enable_block_step(struct task_struct *child)
219 : : {
220 : 0 : enable_step(child, 1);
221 : 0 : }
222 : :
223 : 110271 : void user_disable_single_step(struct task_struct *child)
224 : : {
225 : : /*
226 : : * Make sure block stepping (BTF) is disabled.
227 : : */
228 [ - + ]: 110271 : if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
229 : 0 : set_task_blockstep(child, false);
230 : :
231 : : /* Always clear TIF_SINGLESTEP... */
232 : 110271 : clear_tsk_thread_flag(child, TIF_SINGLESTEP);
233 : :
234 : : /* But touch TF only if it was set by us.. */
235 [ - + ]: 110271 : if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
236 : 0 : task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
237 : 110271 : }
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