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

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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>
This commit is contained in:
Mathieu Desnoyers 2007-03-18 01:26:11 -08:00 • committed by Linus Torvalds
parent bad77057ed
commit 303cd1535f
1 changed files with 8 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

13
arch/x86_64/kernel/process.c
View file

@ -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;