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Commit 8bf1101b authored by Jim Keniston's avatar Jim Keniston Committed by Linus Torvalds
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[PATCH] kprobes: Fix return probes on sys_execve 



Fix a bug in kprobes that can cause an Oops or even a crash when a return
probe is installed on one of the following functions: sys_execve,
do_execve, load_*_binary, flush_old_exec, or flush_thread.  The fix is to
remove the call to kprobe_flush_task() in flush_thread().  This fix has
been tested on all architectures for which the return-probes feature has
been implemented (i386, x86_64, ppc64, ia64).  Please apply.

BACKGROUND

Up to now, we have called kprobe_flush_task() under two situations: when a
task exits, and when it execs.  Flushing kretprobe_instances on exit is
correct because (a) do_exit() doesn't return, and (b) one or more
return-probed functions may be active when a task calls do_exit().  Neither
is the case for sys_execve() and its callees.

Initially, the mistaken call to kprobe_flush_task() on exec was harmless
because we put the "real" return address of each active probed function
back in the stack, just to be safe, when we recycled its
kretprobe_instance.  When support for ppc64 and ia64 was added, this safety
measure couldn't be employed, and was eventually dropped even for i386 and
x86_64.  sys_execve() and its callees were informally blacklisted for
return probes until this fix was developed.

Acked-by: default avatarPrasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: default avatarJim Keniston <jkenisto@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 7c72aaf2

arch/i386/kernel/process.c

+0 −7
Original line number Diff line number Diff line
@@ -393,13 +393,6 @@ void flush_thread(void) 
{

	struct task_struct *tsk = current;



	/*

	 * Remove function-return probe instances associated with this task

	 * and put them back on the free list. Do not insert an exit probe for

	 * this function, it will be disabled by kprobe_flush_task if you do.

	 */

	kprobe_flush_task(tsk);



	memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);

	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	

	/*

arch/ia64/kernel/process.c

+0 −7
Original line number Diff line number Diff line
@@ -718,13 +718,6 @@ kernel_thread_helper (int (*fn)(void *), void *arg) 
void

flush_thread (void)

{

	/*

	 * Remove function-return probe instances associated with this task

	 * and put them back on the free list. Do not insert an exit probe for

	 * this function, it will be disabled by kprobe_flush_task if you do.

	 */

	kprobe_flush_task(current);



	/* drop floating-point and debug-register state if it exists: */

	current->thread.flags &= ~(IA64_THREAD_FPH_VALID | IA64_THREAD_DBG_VALID);

	ia64_drop_fpu(current);

arch/powerpc/kernel/process.c

+0 −1
Original line number Diff line number Diff line
@@ -457,7 +457,6 @@ void flush_thread(void) 
	if (t->flags & _TIF_ABI_PENDING)

		t->flags ^= (_TIF_ABI_PENDING | _TIF_32BIT);

#endif

	kprobe_flush_task(current);



#ifndef CONFIG_SMP

	if (last_task_used_math == current)

arch/x86_64/kernel/process.c

+0 −7
Original line number Diff line number Diff line
@@ -351,13 +351,6 @@ void flush_thread(void) 
	struct task_struct *tsk = current;

	struct thread_info *t = current_thread_info();



	/*

	 * Remove function-return probe instances associated with this task

	 * and put them back on the free list. Do not insert an exit probe for

	 * this function, it will be disabled by kprobe_flush_task if you do.

	 */

	kprobe_flush_task(tsk);



	if (t->flags & _TIF_ABI_PENDING)

		t->flags ^= (_TIF_ABI_PENDING | _TIF_IA32);