[PATCH 5.18 124/141] cfi: Fix __cfi_slowpath_diag RCU usage with cpuidle

Greg Kroah-Hartman
2022-06-20T13:08:05Z

From: Sami Tolvanen <samitolvanen@google.com>

commit 57cd6d157eb479f0a8e820fd36b7240845c8a937 upstream.

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: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20220531175910.890307-1-samitolvanen@google.com
Fixes: cf68fffb66d6 ("add support for Clang CFI")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/cfi.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

--- a/kernel/cfi.c
+++ b/kernel/cfi.c
@@ -281,6 +281,8 @@ static inline cfi_check_fn find_module_c
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
* the shadow and __module_address use RCU, so we need to wake it
* up if necessary.
*/
- RCU_NONIDLE({
- if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW))
- fn = find_shadow_check_fn(ptr);
+ rcu_idle = !rcu_is_watching();
+ if (rcu_idle) {
+ local_irq_save(flags);
+ rcu_irq_enter();
+ }

- if (!fn)
- fn = find_module_check_fn(ptr);
- });
+ 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;
}