# \[RFC PATCH 08/14\] BROKEN: context\_tracking: Make context\_tracking\_key \_\_ro\_after\_init - From: Valentin Schneider \ - Date: 2023-07-05 18:18:07 - List: linux-trace-kernel - Page: https://ratatoskr.run/linux-trace-kernel/2023/07/2255238 - Thread: https://ratatoskr.run/linux-trace-kernel/2023/07/2255228/t.md ```text objtool now warns about it: vmlinux.o: warning: objtool: enter_from_user_mode+0x4e: Non __ro_after_init static key "context_tracking_key" in .noinstr section vmlinux.o: warning: objtool: enter_from_user_mode+0x50: Non __ro_after_init static key "context_tracking_key" in .noinstr section vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x60: Non __ro_after_init static key "context_tracking_key" in .noinstr section vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x62: Non __ro_after_init static key "context_tracking_key" in .noinstr section [...] The key can only be enabled (and not disabled) in the __init function ct_cpu_tracker_user(), so mark it as __ro_after_init. BROKEN: the struct static_key lives in a read-only mapping after mark_rodata_ro(), which falls apart when the KVM module is loaded after init and a write to the struct happens due to e.g. guest_state_exit_irqoff() relying on the static key: jump_label_add_module() `\ static_key_set_mod() static_key_set_linked() Signed-off-by: Valentin Schneider --- kernel/context_tracking.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index a09f1c19336ae..4e6cb14272fcb 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -432,7 +432,7 @@ static __always_inline void ct_kernel_enter(bool user, int offset) { } #define CREATE_TRACE_POINTS #include -DEFINE_STATIC_KEY_FALSE(context_tracking_key); +DEFINE_STATIC_KEY_FALSE_RO(context_tracking_key); EXPORT_SYMBOL_GPL(context_tracking_key); static noinstr bool context_tracking_recursion_enter(void) -- 2.31.1 ```