Commit 57cd6d15 authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Kees Cook
Browse files

cfi: Fix __cfi_slowpath_diag RCU usage with cpuidle 



RCU_NONIDLE usage during __cfi_slowpath_diag can result in an invalid
RCU state in the cpuidle code path:

  WARNING: CPU: 1 PID: 0 at kernel/rcu/tree.c:613 rcu_eqs_enter+0xe4/0x138
  ...
  Call trace:
    rcu_eqs_enter+0xe4/0x138
    rcu_idle_enter+0xa8/0x100
    cpuidle_enter_state+0x154/0x3a8
    cpuidle_enter+0x3c/0x58
    do_idle.llvm.6590768638138871020+0x1f4/0x2ec
    cpu_startup_entry+0x28/0x2c
    secondary_start_kernel+0x1b8/0x220
    __secondary_switched+0x94/0x98

Instead, call rcu_irq_enter/exit to wake up RCU only when needed and
disable interrupts for the entire CFI shadow/module check when we do.

Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20220531175910.890307-1-samitolvanen@google.com


Fixes: cf68fffb ("add support for Clang CFI")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent b13baccc

kernel/cfi.c

+16 −6
Original line number Diff line number Diff line
@@ -281,6 +281,8 @@ static inline cfi_check_fn find_module_check_fn(unsigned long ptr) 
static inline cfi_check_fn find_check_fn(unsigned long ptr)

{

	cfi_check_fn fn = NULL;

	unsigned long flags;

	bool rcu_idle;



	if (is_kernel_text(ptr))

		return __cfi_check;
@@ -290,13 +292,21 @@ static inline cfi_check_fn find_check_fn(unsigned long ptr) 
	 * the shadow and __module_address use RCU, so we need to wake it

	 * up if necessary.

	 */

	RCU_NONIDLE({

	rcu_idle = !rcu_is_watching();

	if (rcu_idle) {

		local_irq_save(flags);

		rcu_irq_enter();

	}



	if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW))

		fn = find_shadow_check_fn(ptr);



	if (!fn)

		fn = find_module_check_fn(ptr);

	});



	if (rcu_idle) {

		rcu_irq_exit();

		local_irq_restore(flags);

	}



	return fn;

}