Commit 14c4c8e4 authored by Elliot Berman's avatar Elliot Berman Committed by Kees Cook
Browse files

cfi: Use rcu_read_{un}lock_sched_notrace 



If rcu_read_lock_sched tracing is enabled, the tracing subsystem can
perform a jump which needs to be checked by CFI. For example, stm_ftrace
source is enabled as a module and hooks into enabled ftrace events. This
can cause an recursive loop where find_shadow_check_fn ->
rcu_read_lock_sched -> (call to stm_ftrace generates cfi slowpath) ->
find_shadow_check_fn -> rcu_read_lock_sched -> ...

To avoid the recursion, either the ftrace codes needs to be marked with
__no_cfi or CFI should not trace. Use the "_notrace" in CFI to avoid
tracing so that CFI can guard ftrace.

Signed-off-by: default avatarElliot Berman <quic_eberman@quicinc.com>
Reviewed-by: default avatarSami Tolvanen <samitolvanen@google.com>
Cc: stable@vger.kernel.org
Fixes: cf68fffb ("add support for Clang CFI")
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210811155914.19550-1-quic_eberman@quicinc.com
parent 36a21d51

kernel/cfi.c

+4 −4
Original line number Diff line number Diff line
@@ -248,9 +248,9 @@ static inline cfi_check_fn find_shadow_check_fn(unsigned long ptr) 
{

	cfi_check_fn fn;



	rcu_read_lock_sched();

	rcu_read_lock_sched_notrace();

	fn = ptr_to_check_fn(rcu_dereference_sched(cfi_shadow), ptr);

	rcu_read_unlock_sched();

	rcu_read_unlock_sched_notrace();



	return fn;

}
@@ -269,11 +269,11 @@ static inline cfi_check_fn find_module_check_fn(unsigned long ptr) 
	cfi_check_fn fn = NULL;

	struct module *mod;



	rcu_read_lock_sched();

	rcu_read_lock_sched_notrace();

	mod = __module_address(ptr);

	if (mod)

		fn = mod->cfi_check;

	rcu_read_unlock_sched();

	rcu_read_unlock_sched_notrace();



	return fn;

}