genirq: Move interrupt thread exit_work object to irqaction

irq_thread() registers irq_thread_dtor() as exit task_work using a
stack-allocated callback_head.  On normal interrupt thread exit, this work
gets cancelled and never runs.

On x86, an abnormal interrupt thread exit (e.g. handler oops) discards the
stack, including the callback_head, while that callback_head is still
pending. By the time exit_task_work() runs, the stack memory formerly
backing callback_head is already clobbered.

  irq_thread()                      <-- on_exit_work allocated
    ** IRQ handler faults **
    oops_end()
      rewind_stack_and_make_dead()  <-- on_exit_work freed
  make_task_dead()
    do_exit(SIGSEGV)
      ...
      exit_shm()                    <-- on_exit_work clobbered
      ...
      exit_task_work()              <-- stack use-after-free
        exit_shm()+0x30             <-- wild jump to return addr

Thus, a benign threaded IRQ oops (e.g. a NULL pointer deref) is
turned into a wild jump. This is caught by kernel IBT:

  ** first fault **
  Oops: general protection fault, kernel NULL pointer dereference 0x3c0: 0000 [#1] SMP NOPTI
  ...
  ** second fault **
  Missing ENDBR: exit_shm+0x30/0x1c0
  kernel BUG at arch/x86/kernel/cet.c:133!
  ...
   ? task_work_run+0x5c/0x90
   ? do_exit+0x209/0x460
   ? rewind_stack_and_make_dead+0x16/0x20
  ...
  note: irq/165-AudioDS[1427] exited with irqs disabled
  Fixing recursive fault but reboot is needed!

Fix this by storing the callback_head in struct irqaction.  The irqaction
is only freed once irq_thread_dtor() finishes.

Fixes: 2deb4be28077 ("x86/dumpstack: When OOPSing, rewind the stack before do_exit()")
Signed-off-by: Richard Patel <ripatel@wii.dev>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20261009145842.1616117-3-ripatel@wii.dev

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 3bf969ad8fe0..50745608dc15 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -119,6 +119,7 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
  * @thread_flags:	flags related to @thread
  * @thread_mask:	bitmask for keeping track of @thread activity
  * @dir:	pointer to the proc/irq/NN/name entry
+ * @thread_dtor:	task_work for @thread irregular exit cleanup
  */
 struct irqaction {
 	irq_handler_t		handler;
@@ -137,6 +138,7 @@ struct irqaction {
 	unsigned long		thread_mask;
 	const char		*name;
 	struct proc_dir_entry	*dir;
+	struct callback_head	thread_dtor;
 } ____cacheline_internodealigned_in_smp;
 
 extern irqreturn_t no_action(int cpl, void *dev_id);