diff options
Diffstat (limited to 'arch/x86/kernel/step.c')
| -rw-r--r-- | arch/x86/kernel/step.c | 106 |
1 files changed, 65 insertions, 41 deletions
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index 071ff479823..9b4d51d0c0d 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -4,6 +4,7 @@ #include <linux/sched.h> #include <linux/mm.h> #include <linux/ptrace.h> +#include <asm/desc.h> unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) { @@ -23,7 +24,7 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re * and APM bios ones we just ignore here. */ if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { - u32 *desc; + struct desc_struct *desc; unsigned long base; seg &= ~7UL; @@ -33,12 +34,10 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re addr = -1L; /* bogus selector, access would fault */ else { desc = child->mm->context.ldt + seg; - base = ((desc[0] >> 16) | - ((desc[1] & 0xff) << 16) | - (desc[1] & 0xff000000)); + base = get_desc_base(desc); /* 16-bit code segment? */ - if (!((desc[1] >> 22) & 1)) + if (!desc->d) addr &= 0xffff; addr += base; } @@ -75,7 +74,7 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) #ifdef CONFIG_X86_64 case 0x40 ... 0x4f: - if (regs->cs != __USER_CS) + if (!user_64bit_mode(regs)) /* 32-bit mode: register increment */ return 0; /* 64-bit mode: REX prefix */ @@ -105,6 +104,20 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) static int enable_single_step(struct task_struct *child) { struct pt_regs *regs = task_pt_regs(child); + unsigned long oflags; + + /* + * If we stepped into a sysenter/syscall insn, it trapped in + * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. + * If user-mode had set TF itself, then it's still clear from + * do_debug() and we need to set it again to restore the user + * state so we don't wrongly set TIF_FORCED_TF below. + * If enable_single_step() was used last and that is what + * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are + * already set and our bookkeeping is fine. + */ + if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) + regs->flags |= X86_EFLAGS_TF; /* * Always set TIF_SINGLESTEP - this guarantees that @@ -113,11 +126,7 @@ static int enable_single_step(struct task_struct *child) */ set_tsk_thread_flag(child, TIF_SINGLESTEP); - /* - * If TF was already set, don't do anything else - */ - if (regs->flags & X86_EFLAGS_TF) - return 0; + oflags = regs->flags; /* Set TF on the kernel stack.. */ regs->flags |= X86_EFLAGS_TF; @@ -126,29 +135,54 @@ static int enable_single_step(struct task_struct *child) * ..but if TF is changed by the instruction we will trace, * don't mark it as being "us" that set it, so that we * won't clear it by hand later. + * + * Note that if we don't actually execute the popf because + * of a signal arriving right now or suchlike, we will lose + * track of the fact that it really was "us" that set it. */ - if (is_setting_trap_flag(child, regs)) + if (is_setting_trap_flag(child, regs)) { + clear_tsk_thread_flag(child, TIF_FORCED_TF); return 0; + } + + /* + * If TF was already set, check whether it was us who set it. + * If not, we should never attempt a block step. + */ + if (oflags & X86_EFLAGS_TF) + return test_tsk_thread_flag(child, TIF_FORCED_TF); set_tsk_thread_flag(child, TIF_FORCED_TF); return 1; } -/* - * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running. - */ -static void write_debugctlmsr(struct task_struct *child, unsigned long val) +void set_task_blockstep(struct task_struct *task, bool on) { - if (child->thread.debugctlmsr == val) - return; - - child->thread.debugctlmsr = val; - - if (child != current) - return; + unsigned long debugctl; - wrmsrl(MSR_IA32_DEBUGCTLMSR, val); + /* + * Ensure irq/preemption can't change debugctl in between. + * Note also that both TIF_BLOCKSTEP and debugctl should + * be changed atomically wrt preemption. + * + * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if + * task is current or it can't be running, otherwise we can race + * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but + * PTRACE_KILL is not safe. + */ + local_irq_disable(); + debugctl = get_debugctlmsr(); + if (on) { + debugctl |= DEBUGCTLMSR_BTF; + set_tsk_thread_flag(task, TIF_BLOCKSTEP); + } else { + debugctl &= ~DEBUGCTLMSR_BTF; + clear_tsk_thread_flag(task, TIF_BLOCKSTEP); + } + if (task == current) + update_debugctlmsr(debugctl); + local_irq_enable(); } /* @@ -160,20 +194,13 @@ static void enable_step(struct task_struct *child, bool block) * Make sure block stepping (BTF) is not enabled unless it should be. * Note that we don't try to worry about any is_setting_trap_flag() * instructions after the first when using block stepping. - * So noone should try to use debugger block stepping in a program + * So no one should try to use debugger block stepping in a program * that uses user-mode single stepping itself. */ - if (enable_single_step(child) && block) { - set_tsk_thread_flag(child, TIF_DEBUGCTLMSR); - write_debugctlmsr(child, - child->thread.debugctlmsr | DEBUGCTLMSR_BTF); - } else { - write_debugctlmsr(child, - child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF); - - if (!child->thread.debugctlmsr) - clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR); - } + if (enable_single_step(child) && block) + set_task_blockstep(child, true); + else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) + set_task_blockstep(child, false); } void user_enable_single_step(struct task_struct *child) @@ -191,11 +218,8 @@ void user_disable_single_step(struct task_struct *child) /* * Make sure block stepping (BTF) is disabled. */ - write_debugctlmsr(child, - child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF); - - if (!child->thread.debugctlmsr) - clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR); + if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) + set_task_blockstep(child, false); /* Always clear TIF_SINGLESTEP... */ clear_tsk_thread_flag(child, TIF_SINGLESTEP); |