Messages in this thread | | | Date | Fri, 8 May 2020 17:23:09 +0900 | From | Masami Hiramatsu <> | Subject | Re: [patch V4 part 2 07/18] context_tracking: Ensure that the critical path cannot be instrumented |
| |
On Tue, 05 May 2020 15:41:19 +0200 Thomas Gleixner <tglx@linutronix.de> wrote:
> 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 <tglx@linutronix.de>
Looks good to me.
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Thanks!
> --- > 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(-) > > --- 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 c > * 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; > --- 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_enab > 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; > } > --- 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_e > 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_e > * 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_s > * on the tick. > */ > if (state == CONTEXT_USER) { > + instr_begin(); > trace_user_enter(0); > vtime_user_enter(current); > + instr_end(); > } > rcu_user_enter(); > } > @@ -99,7 +101,6 @@ void __context_tracking_enter(enum ctx_s > } > 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_en > * 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_st > */ > rcu_user_exit(); > if (state == CONTEXT_USER) { > + instr_begin(); > vtime_user_exit(current); > trace_user_exit(0); > + instr_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) >
-- Masami Hiramatsu <mhiramat@kernel.org>
| |