[PATCH 1/1] cfi: Use rcu_read_{un}lock_sched_notrace
From: Elliot Berman
Date: Wed Aug 11 2021 - 11:59:59 EST
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@xxxxxxxxxxx>
---
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;
}
--
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