Fixing the stable@xxxxxxxxxx CC.
----- On Nov 11, 2017, at 10:03 AM, Mathieu Desnoyers mathieu.desnoyers@xxxxxxxxxxxx wrote:
> x86 has a missing core serializing instruction in migration scenarios.
>
> Given that x86-32 can return to user-space with sysexit, and x86-64
> through sysretq and sysretl, which are not core serializing, the
> following user-space self-modifiying code (JIT) scenario can occur:
>
> CPU 0 CPU 1
>
> User-space self-modify code
> Preempted
> migrated ->
> scheduler selects task
> Return to user-space (iret or sysexit)
> User-space issues sync_core()
> <- migrated
> scheduler selects task
> Return to user-space (sysexit)
> jump to modified code
> Run modified code without sync_core() -> bug.
>
> This migration pattern can return to user-space through sysexit,
> sysretl, or sysretq, which are not core serializing, and therefore
> breaks sequential consistency expectations from a single-threaded
> process.
>
> Fix this issue by introducing sync_core_before_usermode(), invoked the
> first time a runqueue finishes a task switch after receiving a migrated
> thread.
>
> Architectures defining the sync_core_before_usermode() static inline
> need to define ARCH_HAS_SYNC_CORE_BEFORE_USERMODE.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> CC: Andy Lutomirski <luto@xxxxxxxxxx>
> CC: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> CC: Boqun Feng <boqun.feng@xxxxxxxxx>
> CC: Andrew Hunter <ahh@xxxxxxxxxx>
> CC: Maged Michael <maged.michael@xxxxxxxxx>
> CC: Avi Kivity <avi@xxxxxxxxxxxx>
> CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> CC: Paul Mackerras <paulus@xxxxxxxxx>
> CC: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> CC: Dave Watson <davejwatson@xxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: Ingo Molnar <mingo@xxxxxxxxxx>
> CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
> CC: Andrea Parri <parri.andrea@xxxxxxxxx>
> CC: Russell King <linux@xxxxxxxxxxxxxxx>
> CC: Greg Hackmann <ghackmann@xxxxxxxxxx>
> CC: Will Deacon <will.deacon@xxxxxxx>
> CC: David Sehr <sehr@xxxxxxxxxx>
> CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> CC: x86@xxxxxxxxxx
> CC: linux-arch@xxxxxxxxxxxxxxx
> CC: stable@xxxxxxxxxx
>
> ---
> Changes since v1:
> - Fold patch introducing sync_core_before_usermode and the fix
> into a single patch.
> - CC stable@xxxxxxxxxx
> ---
> arch/x86/Kconfig | 1 +
> arch/x86/include/asm/processor.h | 10 ++++++++++
> include/linux/processor.h | 6 ++++++
> kernel/sched/core.c | 7 +++++++
> kernel/sched/sched.h | 1 +
> 5 files changed, 25 insertions(+)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 2fdb23313dd5..b27456f04cc6 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -62,6 +62,7 @@ config X86
> select ARCH_HAS_SG_CHAIN
> select ARCH_HAS_STRICT_KERNEL_RWX
> select ARCH_HAS_STRICT_MODULE_RWX
> + select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
> select ARCH_HAS_UBSAN_SANITIZE_ALL
> select ARCH_HAS_ZONE_DEVICE if X86_64
> select ARCH_HAVE_NMI_SAFE_CMPXCHG
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index bdac19ab2488..6daf70a8c81c 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -706,6 +706,16 @@ static inline void sync_core(void)
> #endif
> }
>
> +/*
> + * Ensure that a core serializing instruction is issued before returning
> + * to user-mode. x86 implements return to user-space through sysexit,
> + * sysretl, and sysretq, which are not core serializing.
> + */
> +static inline void sync_core_before_usermode(void)
> +{
> + sync_core();
> +}
> +
> extern void select_idle_routine(const struct cpuinfo_x86 *c);
> extern void amd_e400_c1e_apic_setup(void);
>
> diff --git a/include/linux/processor.h b/include/linux/processor.h
> index dbc952eec869..7d12e6fa050e 100644
> --- a/include/linux/processor.h
> +++ b/include/linux/processor.h
> @@ -68,4 +68,10 @@ do { \
>
> #endif
>
> +#ifndef ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
> +static inline sync_core_before_usermode(void)
> +{
> +}
> +#endif
> +
> #endif /* _LINUX_PROCESSOR_H */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d17c5da523a0..39c0bbe8f259 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -927,6 +927,7 @@ static struct rq *move_queued_task(struct rq *rq, struct
> rq_flags *rf,
>
> rq_lock(rq, rf);
> BUG_ON(task_cpu(p) != new_cpu);
> + rq->need_sync_core = 1;
> enqueue_task(rq, p, 0);
> p->on_rq = TASK_ON_RQ_QUEUED;
> check_preempt_curr(rq, p, 0);
> @@ -2654,6 +2655,12 @@ static struct rq *finish_task_switch(struct task_struct
> *prev)
> * to use.
> */
> smp_mb__after_unlock_lock();
> +#ifdef CONFIG_SMP
> + if (unlikely(rq->need_sync_core)) {
> + sync_core_before_usermode();
> + rq->need_sync_core = 0;
> + }
> +#endif
> finish_lock_switch(rq, prev);
> finish_arch_post_lock_switch();
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 3b448ba82225..e02cc362637c 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -734,6 +734,7 @@ struct rq {
> /* For active balancing */
> int active_balance;
> int push_cpu;
> + int need_sync_core;
> struct cpu_stop_work active_balance_work;
> /* cpu of this runqueue: */
> int cpu;
> --
> 2.11.0
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com