From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 8 Jan 2025 10:04:50 +0100
Subject: [PATCH 21/28] cfi: Use RCU while invoking __module_address().
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.
The _notrace() variant was introduced in commit 14c4c8e41511a ("cfi: Use
rcu_read_{un}lock_sched_notrace"). The recursive case where
__cfi_slowpath_diag() could end up calling itself is no longer present,
as all that logic is gone since commit 89245600941e ("cfi: Switch to
-fsanitize=kcfi").
Sami Tolvanen said that KCFI checks don't perform function calls.
Elliot Berman verified it with
| modprobe -a dummy_stm stm_ftrace stm_p_basic
| mkdir -p /sys/kernel/config/stp-policy/dummy_stm.0.my-policy/default
| echo function > /sys/kernel/tracing/current_tracer
| echo 1 > /sys/kernel/tracing/tracing_on
| echo dummy_stm.0 > /sys/class/stm_source/ftrace/stm_source_link
Replace the rcu_read_lock_sched_notrace() section around
__module_address() with RCU.
Cc: Elliot Berman <quic_eberman@quicinc.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: llvm@lists.linux.dev
Tested-by: Elliot Berman <elliot.berman@oss.qualcomm.com> # sm8650-qrd
Link: https://lore.kernel.org/all/20241230185812429-0800.eberman@hu-eberman-lv.qualcomm.com
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250108090457.512198-22-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/cfi.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
@ kernel/cfi.c:74 @ static bool is_module_cfi_trap(unsigned
struct module *mod;
bool found = false;
- rcu_read_lock_sched_notrace();
-
+ guard(rcu)();
mod = __module_address(addr);
if (mod)
found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end);
- rcu_read_unlock_sched_notrace();
-
return found;
}
#else /* CONFIG_MODULES */