From 303cd1535f6257b9fd8214534ca87b1a1567a2c5 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Sun, 18 Mar 2007 01:26:11 -0800
Subject: [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>
---
arch/x86_64/kernel/process.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index cbbc6adc1a..d8d5ccc245 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -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;
--
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