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prctl: Add force disable speculation

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For certain use cases it is desired to enforce mitigations so they cannot
be undone afterwards. That's important for loader stubs which want to
prevent a child from disabling the mitigation again. Will also be used for
seccomp(). The extra state preserving of the prctl state for SSB is a
preparatory step for EBPF dymanic speculation control.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner
2018-05-03 22:09:15 +02:00
parent f9544b2b07
commit 356e4bfff2
5 changed files with 59 additions and 24 deletions
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35
arch/x86/kernel/cpu/bugs.c
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@@ -533,21 +533,37 @@ static void ssb_select_mitigation()
static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
{
bool rds = !!test_tsk_thread_flag(task, TIF_RDS);
bool update;
if (ssb_mode != SPEC_STORE_BYPASS_PRCTL)
return -ENXIO;
if (ctrl == PR_SPEC_ENABLE)
clear_tsk_thread_flag(task, TIF_RDS);
else
set_tsk_thread_flag(task, TIF_RDS);
switch (ctrl) {
case PR_SPEC_ENABLE:
/* If speculation is force disabled, enable is not allowed */
if (task_spec_ssb_force_disable(task))
return -EPERM;
task_clear_spec_ssb_disable(task);
update = test_and_clear_tsk_thread_flag(task, TIF_RDS);
break;
case PR_SPEC_DISABLE:
task_set_spec_ssb_disable(task);
update = !test_and_set_tsk_thread_flag(task, TIF_RDS);
break;
case PR_SPEC_FORCE_DISABLE:
task_set_spec_ssb_disable(task);
task_set_spec_ssb_force_disable(task);
update = !test_and_set_tsk_thread_flag(task, TIF_RDS);
break;
default:
return -ERANGE;
}
/*
* If being set on non-current task, delay setting the CPU
* mitigation until it is next scheduled.
*/
if (task == current && rds != !!test_tsk_thread_flag(task, TIF_RDS))
if (task == current && update)
speculative_store_bypass_update();
return 0;
@@ -559,7 +575,9 @@ static int ssb_prctl_get(struct task_struct *task)
case SPEC_STORE_BYPASS_DISABLE:
return PR_SPEC_DISABLE;
case SPEC_STORE_BYPASS_PRCTL:
if (test_tsk_thread_flag(task, TIF_RDS))
if (task_spec_ssb_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
if (task_spec_ssb_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
default:
@@ -572,9 +590,6 @@ static int ssb_prctl_get(struct task_struct *task)
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
unsigned long ctrl)
{
if (ctrl != PR_SPEC_ENABLE && ctrl != PR_SPEC_DISABLE)
return -ERANGE;
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_set(task, ctrl);