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sched: Add task_work callback for paranoid L1D flush

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The upcoming paranoid L1D flush infrastructure allows to conditionally
(opt-in) flush L1D in switch_mm() as a defense against potential new side
channels or for paranoia reasons. As the flush makes only sense when a task
runs on a non-SMT enabled core, because SMT siblings share L1, the
switch_mm() logic will kill a task which is flagged for L1D flush when it
is running on a SMT thread.

Add a taskwork callback so switch_mm() can queue a SIG_KILL command which
is invoked when the task tries to return to user space.

Signed-off-by: Balbir Singh <sblbir@amazon.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210108121056.21940-1-sblbir@amazon.com
This commit is contained in:
Balbir Singh 2021-04-26 21:59:11 +02:00 committed by Thomas Gleixner
parent 371b09c6fd
commit 58e106e725
2 changed files with 13 additions and 0 deletions
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3
arch/Kconfig
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@ -1282,6 +1282,9 @@ config ARCH_SPLIT_ARG64
config ARCH_HAS_ELFCORE_COMPAT
bool
config ARCH_HAS_PARANOID_L1D_FLUSH
bool
source "kernel/gcov/Kconfig"
source "scripts/gcc-plugins/Kconfig"

10
include/linux/sched.h
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@ -1400,6 +1400,16 @@ struct task_struct {
struct llist_head kretprobe_instances;
#endif
#ifdef CONFIG_ARCH_HAS_PARANOID_L1D_FLUSH
/*
* If L1D flush is supported on mm context switch
* then we use this callback head to queue kill work
* to kill tasks that are not running on SMT disabled
* cores
*/
struct callback_head l1d_flush_kill;
#endif
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.