Commit 303cd153 authored Mar 18, 2007 by Mathieu Desnoyers Committed by Linus Torvalds Mar 18, 2007

[PATCH] Fix atomicity of TIF update in flush_thread() for x86_64



Fix atomicity of TIF update in flush_thread() for x86_64

Race :

parent process executing :
sys_ptrace()
 (lock_kernel())
 (ptrace_get_task_struct(pid))
 arch_ptrace()
   ptrace_detach()
     ptrace_disable(child);
       clear_singlestep(child);
         clear_tsk_thread_flag(child, TIF_SINGLESTEP);
         (which clears the TIF_SINGLESTEP flag atomically from a different
	  process)
 (put_task_struct(child))
 (unlock_kernel())

And at the same time, in the child process :
sys_execve()
 do_execve()
   search_binary_handler()
     load_elf_binary()
       flush_old_exec()
         flush_thread()
           doing a non-atomic thread flag update

Signed-off-by: Rebecca Schultz <rschultz@google.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bad77057

arch/x86_64/kernel/process.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -382,14 +382,17 @@ void exit_thread(void)
		void flush_thread(void)
		{
		struct task_struct *tsk = current;
		struct thread_info *t = current_thread_info();

		if (t->flags & _TIF_ABI_PENDING) {
		t->flags ^= (_TIF_ABI_PENDING \| _TIF_IA32);
		if (t->flags & _TIF_IA32)
		if (test_tsk_thread_flag(tsk, TIF_ABI_PENDING)) {
		clear_tsk_thread_flag(tsk, TIF_ABI_PENDING);
		if (test_tsk_thread_flag(tsk, TIF_IA32)) {
		clear_tsk_thread_flag(tsk, TIF_IA32);
		} else {
		set_tsk_thread_flag(tsk, TIF_IA32);
		current_thread_info()->status \|= TS_COMPAT;
		}
		t->flags &= ~_TIF_DEBUG;
		}
		clear_tsk_thread_flag(tsk, TIF_DEBUG);

		tsk->thread.debugreg0 = 0;
		tsk->thread.debugreg1 = 0;