x86: debugctlmsr arch_has_block_step
This implements user-mode step-until-branch on x86 using the BTF bit in MSR_IA32_DEBUGCTLMSR. It's just like single-step, only less so. Signed-off-by: Roland McGrath <roland@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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4 changed files with 80 additions and 3 deletions
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@ -107,7 +107,10 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
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return 0;
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}
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void user_enable_single_step(struct task_struct *child)
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/*
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* Enable single-stepping. Return nonzero if user mode is not using TF itself.
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*/
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static int enable_single_step(struct task_struct *child)
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{
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struct pt_regs *regs = task_pt_regs(child);
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@ -122,7 +125,7 @@ void user_enable_single_step(struct task_struct *child)
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* If TF was already set, don't do anything else
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*/
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if (regs->eflags & X86_EFLAGS_TF)
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return;
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return 0;
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/* Set TF on the kernel stack.. */
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regs->eflags |= X86_EFLAGS_TF;
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@ -133,13 +136,68 @@ void user_enable_single_step(struct task_struct *child)
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* won't clear it by hand later.
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*/
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if (is_setting_trap_flag(child, regs))
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return;
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return 0;
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set_tsk_thread_flag(child, TIF_FORCED_TF);
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return 1;
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}
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/*
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* Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running.
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*/
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static void write_debugctlmsr(struct task_struct *child, unsigned long val)
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{
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child->thread.debugctlmsr = val;
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if (child != current)
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return;
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#ifdef CONFIG_X86_64
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wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
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#else
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wrmsr(MSR_IA32_DEBUGCTLMSR, val, 0);
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#endif
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}
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/*
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* Enable single or block step.
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*/
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static void enable_step(struct task_struct *child, bool block)
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{
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/*
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* Make sure block stepping (BTF) is not enabled unless it should be.
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* Note that we don't try to worry about any is_setting_trap_flag()
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* instructions after the first when using block stepping.
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* So noone should try to use debugger block stepping in a program
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* that uses user-mode single stepping itself.
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*/
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if (enable_single_step(child) && block) {
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set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
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write_debugctlmsr(child, DEBUGCTLMSR_BTF);
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} else if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR)) {
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write_debugctlmsr(child, 0);
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}
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}
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void user_enable_single_step(struct task_struct *child)
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{
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enable_step(child, 0);
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}
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void user_enable_block_step(struct task_struct *child)
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{
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enable_step(child, 1);
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}
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void user_disable_single_step(struct task_struct *child)
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{
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/*
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* Make sure block stepping (BTF) is disabled.
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*/
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if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR))
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write_debugctlmsr(child, 0);
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/* Always clear TIF_SINGLESTEP... */
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clear_tsk_thread_flag(child, TIF_SINGLESTEP);
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@ -837,6 +837,12 @@ fastcall void __kprobes do_debug(struct pt_regs * regs, long error_code)
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get_debugreg(condition, 6);
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/*
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* The processor cleared BTF, so don't mark that we need it set.
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*/
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clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
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tsk->thread.debugctlmsr = 0;
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if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
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SIGTRAP) == NOTIFY_STOP)
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return;
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@ -850,6 +850,12 @@ asmlinkage void __kprobes do_debug(struct pt_regs * regs,
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get_debugreg(condition, 6);
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/*
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* The processor cleared BTF, so don't mark that we need it set.
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*/
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clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
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tsk->thread.debugctlmsr = 0;
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if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
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SIGTRAP) == NOTIFY_STOP)
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return;
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@ -150,6 +150,13 @@ enum {
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extern void user_enable_single_step(struct task_struct *);
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extern void user_disable_single_step(struct task_struct *);
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extern void user_enable_block_step(struct task_struct *);
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#ifdef CONFIG_X86_DEBUGCTLMSR
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#define arch_has_block_step() (1)
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#else
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#define arch_has_block_step() (boot_cpu_data.x86 >= 6)
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#endif
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struct user_desc;
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extern int do_get_thread_area(struct task_struct *p, int idx,
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struct user_desc __user *info);
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