From 0372007f5a79d61d3cb48a507717b9afb5d6addd Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 4 Mar 2020 11:05:22 +0100 Subject: [PATCH] context_tracking: Ensure that the critical path cannot be instrumented context tracking lacks a few protection mechanisms against instrumentation: - While the core functions are marked NOKPROBE they lack protection against function tracing which is required as the function entry/exit points can be utilized by BPF. - static functions invoked from the protected functions need to be marked as well as they can be instrumented otherwise. - using plain inline allows the compiler to emit traceable and probable functions. Fix this by marking the functions noinstr and converting the plain inlines to __always_inline. The NOKPROBE_SYMBOL() annotations are removed as the .noinstr.text section is already excluded from being probed. Cures the following objtool warnings: vmlinux.o: warning: objtool: enter_from_user_mode()+0x34: call to __context_tracking_exit() leaves .noinstr.text section vmlinux.o: warning: objtool: prepare_exit_to_usermode()+0x29: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: syscall_return_slowpath()+0x29: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: do_syscall_64()+0x7f: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: do_int80_syscall_32()+0x3d: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: do_fast_syscall_32()+0x9c: call to __context_tracking_enter() leaves .noinstr.text section and generates new ones... Signed-off-by: Thomas Gleixner Reviewed-by: Masami Hiramatsu Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200505134340.811520478@linutronix.de --- include/linux/context_tracking.h | 6 +++--- include/linux/context_tracking_state.h | 6 +++--- kernel/context_tracking.c | 14 ++++++++------ 3 files changed, 14 insertions(+), 12 deletions(-) diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index 8cac62ee6add..981b880d5b60 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -33,13 +33,13 @@ static inline void user_exit(void) } /* Called with interrupts disabled. */ -static inline void user_enter_irqoff(void) +static __always_inline void user_enter_irqoff(void) { if (context_tracking_enabled()) __context_tracking_enter(CONTEXT_USER); } -static inline void user_exit_irqoff(void) +static __always_inline void user_exit_irqoff(void) { if (context_tracking_enabled()) __context_tracking_exit(CONTEXT_USER); @@ -75,7 +75,7 @@ static inline void exception_exit(enum ctx_state prev_ctx) * is enabled. If context tracking is disabled, returns * CONTEXT_DISABLED. This should be used primarily for debugging. */ -static inline enum ctx_state ct_state(void) +static __always_inline enum ctx_state ct_state(void) { return context_tracking_enabled() ? this_cpu_read(context_tracking.state) : CONTEXT_DISABLED; diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h index e7fe6678b7ad..65a60d3313b0 100644 --- a/include/linux/context_tracking_state.h +++ b/include/linux/context_tracking_state.h @@ -26,12 +26,12 @@ struct context_tracking { extern struct static_key_false context_tracking_key; DECLARE_PER_CPU(struct context_tracking, context_tracking); -static inline bool context_tracking_enabled(void) +static __always_inline bool context_tracking_enabled(void) { return static_branch_unlikely(&context_tracking_key); } -static inline bool context_tracking_enabled_cpu(int cpu) +static __always_inline bool context_tracking_enabled_cpu(int cpu) { return context_tracking_enabled() && per_cpu(context_tracking.active, cpu); } @@ -41,7 +41,7 @@ static inline bool context_tracking_enabled_this_cpu(void) return context_tracking_enabled() && __this_cpu_read(context_tracking.active); } -static inline bool context_tracking_in_user(void) +static __always_inline bool context_tracking_in_user(void) { return __this_cpu_read(context_tracking.state) == CONTEXT_USER; } diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index ce430885c26c..36a98c48aedc 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -31,7 +31,7 @@ EXPORT_SYMBOL_GPL(context_tracking_key); DEFINE_PER_CPU(struct context_tracking, context_tracking); EXPORT_SYMBOL_GPL(context_tracking); -static bool context_tracking_recursion_enter(void) +static noinstr bool context_tracking_recursion_enter(void) { int recursion; @@ -45,7 +45,7 @@ static bool context_tracking_recursion_enter(void) return false; } -static void context_tracking_recursion_exit(void) +static __always_inline void context_tracking_recursion_exit(void) { __this_cpu_dec(context_tracking.recursion); } @@ -59,7 +59,7 @@ static void context_tracking_recursion_exit(void) * instructions to execute won't use any RCU read side critical section * because this function sets RCU in extended quiescent state. */ -void __context_tracking_enter(enum ctx_state state) +void noinstr __context_tracking_enter(enum ctx_state state) { /* Kernel threads aren't supposed to go to userspace */ WARN_ON_ONCE(!current->mm); @@ -77,8 +77,10 @@ void __context_tracking_enter(enum ctx_state state) * on the tick. */ if (state == CONTEXT_USER) { + instrumentation_begin(); trace_user_enter(0); vtime_user_enter(current); + instrumentation_end(); } rcu_user_enter(); } @@ -99,7 +101,6 @@ void __context_tracking_enter(enum ctx_state state) } context_tracking_recursion_exit(); } -NOKPROBE_SYMBOL(__context_tracking_enter); EXPORT_SYMBOL_GPL(__context_tracking_enter); void context_tracking_enter(enum ctx_state state) @@ -142,7 +143,7 @@ NOKPROBE_SYMBOL(context_tracking_user_enter); * This call supports re-entrancy. This way it can be called from any exception * handler without needing to know if we came from userspace or not. */ -void __context_tracking_exit(enum ctx_state state) +void noinstr __context_tracking_exit(enum ctx_state state) { if (!context_tracking_recursion_enter()) return; @@ -155,15 +156,16 @@ void __context_tracking_exit(enum ctx_state state) */ rcu_user_exit(); if (state == CONTEXT_USER) { + instrumentation_begin(); vtime_user_exit(current); trace_user_exit(0); + instrumentation_end(); } } __this_cpu_write(context_tracking.state, CONTEXT_KERNEL); } context_tracking_recursion_exit(); } -NOKPROBE_SYMBOL(__context_tracking_exit); EXPORT_SYMBOL_GPL(__context_tracking_exit); void context_tracking_exit(enum ctx_state state)