1 // SPDX-License-Identifier: GPL-2.0
3 * x86 single-step support code, common to 32-bit and 64-bit.
5 #include <linux/sched.h>
6 #include <linux/sched/task_stack.h>
8 #include <linux/ptrace.h>
10 #include <asm/mmu_context.h>
12 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
14 unsigned long addr, seg;
18 if (v8086_mode(regs)) {
19 addr = (addr & 0xffff) + (seg << 4);
23 #ifdef CONFIG_MODIFY_LDT_SYSCALL
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.
30 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
31 struct desc_struct *desc;
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 */
41 desc = &child->mm->context.ldt->entries[seg];
42 base = get_desc_base(desc);
44 /* 16-bit code segment? */
49 mutex_unlock(&child->mm->context.lock);
56 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
59 unsigned char opcode[15];
60 unsigned long addr = convert_ip_to_linear(child, regs);
62 copied = access_process_vm(child, addr, opcode, sizeof(opcode),
64 for (i = 0; i < copied; i++) {
72 /* opcode and address size prefixes */
75 /* irrelevant prefixes (segment overrides and repeats) */
79 case 0xf0: case 0xf2: case 0xf3:
84 if (!user_64bit_mode(regs))
85 /* 32-bit mode: register increment */
87 /* 64-bit mode: REX prefix */
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.
109 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
111 static int enable_single_step(struct task_struct *child)
113 struct pt_regs *regs = task_pt_regs(child);
114 unsigned long oflags;
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.
126 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
127 regs->flags |= X86_EFLAGS_TF;
130 * Always set TIF_SINGLESTEP. This will also
131 * cause us to set TF when returning to user mode.
133 set_tsk_thread_flag(child, TIF_SINGLESTEP);
136 * Ensure that a trap is triggered once stepping out of a system
137 * call prior to executing any user instruction.
139 set_task_syscall_work(child, SYSCALL_EXIT_TRAP);
141 oflags = regs->flags;
143 /* Set TF on the kernel stack.. */
144 regs->flags |= X86_EFLAGS_TF;
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.
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.
155 if (is_setting_trap_flag(child, regs)) {
156 clear_tsk_thread_flag(child, TIF_FORCED_TF);
161 * If TF was already set, check whether it was us who set it.
162 * If not, we should never attempt a block step.
164 if (oflags & X86_EFLAGS_TF)
165 return test_tsk_thread_flag(child, TIF_FORCED_TF);
167 set_tsk_thread_flag(child, TIF_FORCED_TF);
172 void set_task_blockstep(struct task_struct *task, bool on)
174 unsigned long debugctl;
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.
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().
186 debugctl = get_debugctlmsr();
188 debugctl |= DEBUGCTLMSR_BTF;
189 set_tsk_thread_flag(task, TIF_BLOCKSTEP);
191 debugctl &= ~DEBUGCTLMSR_BTF;
192 clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
195 update_debugctlmsr(debugctl);
200 * Enable single or block step.
202 static void enable_step(struct task_struct *child, bool block)
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.
211 if (enable_single_step(child) && block)
212 set_task_blockstep(child, true);
213 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
214 set_task_blockstep(child, false);
217 void user_enable_single_step(struct task_struct *child)
219 enable_step(child, 0);
222 void user_enable_block_step(struct task_struct *child)
224 enable_step(child, 1);
227 void user_disable_single_step(struct task_struct *child)
230 * Make sure block stepping (BTF) is disabled.
232 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
233 set_task_blockstep(child, false);
235 /* Always clear TIF_SINGLESTEP... */
236 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
237 clear_task_syscall_work(child, SYSCALL_EXIT_TRAP);
239 /* But touch TF only if it was set by us.. */
240 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
241 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;