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Message-Id: <20200508172309.470787329827c8bfcd797eb1@kernel.org>
Date: Fri, 8 May 2020 17:23:09 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
"Paul E. McKenney" <paulmck@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
Frederic Weisbecker <frederic@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Joel Fernandes <joel@...lfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Brian Gerst <brgerst@...il.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Will Deacon <will@...nel.org>
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@...utronix.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@...utronix.de>
Looks good to me.
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.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@...nel.org>
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