From: Elliot Berman quic_eberman@quicinc.com
[ Upstream commit 14c4c8e41511aa8fba7fb239b20b6539b5bce201 ]
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: Elliot Berman quic_eberman@quicinc.com Reviewed-by: Sami Tolvanen samitolvanen@google.com Cc: stable@vger.kernel.org Fixes: cf68fffb66d6 ("add support for Clang CFI") Signed-off-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20210811155914.19550-1-quic_eberman@quicinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/cfi.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/cfi.c b/kernel/cfi.c index e17a56639766..9594cfd1cf2c 100644 --- a/kernel/cfi.c +++ b/kernel/cfi.c @@ -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; }