diff options
Diffstat (limited to 'arch/x86/kernel/process_32.c')
| -rw-r--r-- | arch/x86/kernel/process_32.c | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 59f4524..00a8fe4 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -58,6 +58,8 @@ #include <asm/idle.h> #include <asm/syscalls.h> #include <asm/ds.h> +#include <asm/debugreg.h> +#include <asm/hw_breakpoint.h> asmlinkage void ret_from_fork(void) __asm__("ret_from_fork"); @@ -262,7 +264,13 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, task_user_gs(p) = get_user_gs(regs); + p->thread.io_bitmap_ptr = NULL; tsk = current; + err = -ENOMEM; + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + if (copy_thread_hw_breakpoint(tsk, p, clone_flags)) + goto out; + if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) { p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr, IO_BITMAP_BYTES, GFP_KERNEL); @@ -282,10 +290,13 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, err = do_set_thread_area(p, -1, (struct user_desc __user *)childregs->si, 0); +out: if (err && p->thread.io_bitmap_ptr) { kfree(p->thread.io_bitmap_ptr); p->thread.io_bitmap_max = 0; } + if (err) + flush_thread_hw_breakpoint(p); clear_tsk_thread_flag(p, TIF_DS_AREA_MSR); p->thread.ds_ctx = NULL; @@ -424,6 +435,23 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) lazy_load_gs(next->gs); percpu_write(current_task, next_p); + /* + * There's a problem with moving the arch_install_thread_hw_breakpoint() + * call before current is updated. Suppose a kernel breakpoint is + * triggered in between the two, the hw-breakpoint handler will see that + * the 'current' task does not have TIF_DEBUG flag set and will think it + * is leftover from an old task (lazy switching) and will erase it. Then + * until the next context switch, no user-breakpoints will be installed. + * + * The real problem is that it's impossible to update both current and + * physical debug registers at the same instant, so there will always be + * a window in which they disagree and a breakpoint might get triggered. + * Since we use lazy switching, we are forced to assume that a + * disagreement means that current is correct and the exception is due + * to lazy debug register switching. + */ + if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG))) + arch_install_thread_hw_breakpoint(next_p); return prev_p; } |