2 * x86 single-step support code, common to 32-bit and 64-bit.
4 #include <linux/sched.h>
6 #include <linux/ptrace.h>
9 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
11 unsigned long addr, seg;
14 seg = regs->cs & 0xffff;
15 if (v8086_mode(regs)) {
16 addr = (addr & 0xffff) + (seg << 4);
21 * We'll assume that the code segments in the GDT
22 * are all zero-based. That is largely true: the
23 * TLS segments are used for data, and the PNPBIOS
24 * and APM bios ones we just ignore here.
26 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
27 struct desc_struct *desc;
32 mutex_lock(&child->mm->context.lock);
33 if (unlikely((seg >> 3) >= child->mm->context.size))
34 addr = -1L; /* bogus selector, access would fault */
36 desc = child->mm->context.ldt + seg;
37 base = get_desc_base(desc);
39 /* 16-bit code segment? */
44 mutex_unlock(&child->mm->context.lock);
50 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
53 unsigned char opcode[15];
54 unsigned long addr = convert_ip_to_linear(child, regs);
56 copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
57 for (i = 0; i < copied; i++) {
65 /* opcode and address size prefixes */
68 /* irrelevant prefixes (segment overrides and repeats) */
72 case 0xf0: case 0xf2: case 0xf3:
77 if (regs->cs != __USER_CS)
78 /* 32-bit mode: register increment */
80 /* 64-bit mode: REX prefix */
87 * pushf: NOTE! We should probably not let
88 * the user see the TF bit being set. But
89 * it's more pain than it's worth to avoid
90 * it, and a debugger could emulate this
91 * all in user space if it _really_ cares.
102 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
104 static int enable_single_step(struct task_struct *child)
106 struct pt_regs *regs = task_pt_regs(child);
107 unsigned long oflags;
110 * If we stepped into a sysenter/syscall insn, it trapped in
111 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
112 * If user-mode had set TF itself, then it's still clear from
113 * do_debug() and we need to set it again to restore the user
114 * state so we don't wrongly set TIF_FORCED_TF below.
115 * If enable_single_step() was used last and that is what
116 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
117 * already set and our bookkeeping is fine.
119 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
120 regs->flags |= X86_EFLAGS_TF;
123 * Always set TIF_SINGLESTEP - this guarantees that
124 * we single-step system calls etc.. This will also
125 * cause us to set TF when returning to user mode.
127 set_tsk_thread_flag(child, TIF_SINGLESTEP);
129 oflags = regs->flags;
131 /* Set TF on the kernel stack.. */
132 regs->flags |= X86_EFLAGS_TF;
135 * ..but if TF is changed by the instruction we will trace,
136 * don't mark it as being "us" that set it, so that we
137 * won't clear it by hand later.
139 * Note that if we don't actually execute the popf because
140 * of a signal arriving right now or suchlike, we will lose
141 * track of the fact that it really was "us" that set it.
143 if (is_setting_trap_flag(child, regs)) {
144 clear_tsk_thread_flag(child, TIF_FORCED_TF);
149 * If TF was already set, check whether it was us who set it.
150 * If not, we should never attempt a block step.
152 if (oflags & X86_EFLAGS_TF)
153 return test_tsk_thread_flag(child, TIF_FORCED_TF);
155 set_tsk_thread_flag(child, TIF_FORCED_TF);
161 * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running.
163 static void write_debugctlmsr(struct task_struct *child, unsigned long val)
165 if (child->thread.debugctlmsr == val)
168 child->thread.debugctlmsr = val;
170 if (child != current)
173 update_debugctlmsr(val);
177 * Enable single or block step.
179 static void enable_step(struct task_struct *child, bool block)
182 * Make sure block stepping (BTF) is not enabled unless it should be.
183 * Note that we don't try to worry about any is_setting_trap_flag()
184 * instructions after the first when using block stepping.
185 * So noone should try to use debugger block stepping in a program
186 * that uses user-mode single stepping itself.
188 if (enable_single_step(child) && block) {
189 set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
190 write_debugctlmsr(child,
191 child->thread.debugctlmsr | DEBUGCTLMSR_BTF);
193 write_debugctlmsr(child,
194 child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
196 if (!child->thread.debugctlmsr)
197 clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
201 void user_enable_single_step(struct task_struct *child)
203 enable_step(child, 0);
206 void user_enable_block_step(struct task_struct *child)
208 enable_step(child, 1);
211 void user_disable_single_step(struct task_struct *child)
214 * Make sure block stepping (BTF) is disabled.
216 write_debugctlmsr(child,
217 child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
219 if (!child->thread.debugctlmsr)
220 clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
222 /* Always clear TIF_SINGLESTEP... */
223 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
225 /* But touch TF only if it was set by us.. */
226 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
227 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;