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prctl: Add force disable speculation
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
parent
f9544b2b07
commit
356e4bfff2
5 changed files with 59 additions and 24 deletions
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@ -25,19 +25,21 @@ PR_GET_SPECULATION_CTRL
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-----------------------
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PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
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which is selected with arg2 of prctl(2). The return value uses bits 0-2 with
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which is selected with arg2 of prctl(2). The return value uses bits 0-3 with
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the following meaning:
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==== ================ ===================================================
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Bit Define Description
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==== ================ ===================================================
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0 PR_SPEC_PRCTL Mitigation can be controlled per task by
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PR_SET_SPECULATION_CTRL
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1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
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disabled
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2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
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enabled
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==== ================ ===================================================
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==== ===================== ===================================================
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Bit Define Description
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==== ===================== ===================================================
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0 PR_SPEC_PRCTL Mitigation can be controlled per task by
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PR_SET_SPECULATION_CTRL
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1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
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disabled
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2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
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enabled
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3 PR_SPEC_FORCE_DISABLE Same as PR_SPEC_DISABLE, but cannot be undone. A
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subsequent prctl(..., PR_SPEC_ENABLE) will fail.
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==== ===================== ===================================================
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If all bits are 0 the CPU is not affected by the speculation misfeature.
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@ -47,9 +49,11 @@ misfeature will fail.
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PR_SET_SPECULATION_CTRL
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-----------------------
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PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which
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is selected by arg2 of :manpage:`prctl(2)` per task. arg3 is used to hand
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in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE.
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in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE or
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PR_SPEC_FORCE_DISABLE.
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Common error codes
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------------------
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@ -70,10 +74,13 @@ Value Meaning
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0 Success
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ERANGE arg3 is incorrect, i.e. it's neither PR_SPEC_ENABLE nor
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PR_SPEC_DISABLE
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PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE
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ENXIO Control of the selected speculation misfeature is not possible.
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See PR_GET_SPECULATION_CTRL.
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EPERM Speculation was disabled with PR_SPEC_FORCE_DISABLE and caller
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tried to enable it again.
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======= =================================================================
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Speculation misfeature controls
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@ -84,3 +91,4 @@ Speculation misfeature controls
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* prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, 0, 0, 0);
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* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
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* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
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* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);
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@ -533,21 +533,37 @@ static void ssb_select_mitigation()
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static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
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{
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bool rds = !!test_tsk_thread_flag(task, TIF_RDS);
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bool update;
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if (ssb_mode != SPEC_STORE_BYPASS_PRCTL)
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return -ENXIO;
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if (ctrl == PR_SPEC_ENABLE)
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clear_tsk_thread_flag(task, TIF_RDS);
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else
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set_tsk_thread_flag(task, TIF_RDS);
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switch (ctrl) {
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case PR_SPEC_ENABLE:
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/* If speculation is force disabled, enable is not allowed */
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if (task_spec_ssb_force_disable(task))
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return -EPERM;
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task_clear_spec_ssb_disable(task);
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update = test_and_clear_tsk_thread_flag(task, TIF_RDS);
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break;
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case PR_SPEC_DISABLE:
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task_set_spec_ssb_disable(task);
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update = !test_and_set_tsk_thread_flag(task, TIF_RDS);
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break;
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case PR_SPEC_FORCE_DISABLE:
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task_set_spec_ssb_disable(task);
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task_set_spec_ssb_force_disable(task);
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update = !test_and_set_tsk_thread_flag(task, TIF_RDS);
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break;
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default:
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return -ERANGE;
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}
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/*
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* If being set on non-current task, delay setting the CPU
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* mitigation until it is next scheduled.
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*/
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if (task == current && rds != !!test_tsk_thread_flag(task, TIF_RDS))
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if (task == current && update)
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speculative_store_bypass_update();
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return 0;
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@ -559,7 +575,9 @@ static int ssb_prctl_get(struct task_struct *task)
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case SPEC_STORE_BYPASS_DISABLE:
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return PR_SPEC_DISABLE;
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case SPEC_STORE_BYPASS_PRCTL:
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if (test_tsk_thread_flag(task, TIF_RDS))
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if (task_spec_ssb_force_disable(task))
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return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
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if (task_spec_ssb_disable(task))
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return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
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return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
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default:
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@ -572,9 +590,6 @@ static int ssb_prctl_get(struct task_struct *task)
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int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
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unsigned long ctrl)
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{
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if (ctrl != PR_SPEC_ENABLE && ctrl != PR_SPEC_DISABLE)
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return -ERANGE;
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switch (which) {
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case PR_SPEC_STORE_BYPASS:
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return ssb_prctl_set(task, ctrl);
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@ -344,6 +344,9 @@ static inline void task_seccomp(struct seq_file *m, struct task_struct *p)
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case PR_SPEC_NOT_AFFECTED:
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seq_printf(m, "not vulnerable");
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break;
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case PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE:
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seq_printf(m, "thread force mitigated");
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break;
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case PR_SPEC_PRCTL | PR_SPEC_DISABLE:
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seq_printf(m, "thread mitigated");
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break;
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@ -1393,7 +1393,8 @@ static inline bool is_percpu_thread(void)
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#define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */
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#define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */
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#define PFA_SPREAD_SLAB 2 /* Spread some slab caches over cpuset */
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#define PFA_SPEC_SSB_DISABLE 3 /* Speculative Store Bypass disabled */
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#define PFA_SPEC_SSB_FORCE_DISABLE 4 /* Speculative Store Bypass force disabled*/
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#define TASK_PFA_TEST(name, func) \
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static inline bool task_##func(struct task_struct *p) \
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@ -1418,6 +1419,13 @@ TASK_PFA_TEST(SPREAD_SLAB, spread_slab)
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TASK_PFA_SET(SPREAD_SLAB, spread_slab)
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TASK_PFA_CLEAR(SPREAD_SLAB, spread_slab)
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TASK_PFA_TEST(SPEC_SSB_DISABLE, spec_ssb_disable)
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TASK_PFA_SET(SPEC_SSB_DISABLE, spec_ssb_disable)
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TASK_PFA_CLEAR(SPEC_SSB_DISABLE, spec_ssb_disable)
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TASK_PFA_TEST(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
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TASK_PFA_SET(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
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static inline void
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current_restore_flags(unsigned long orig_flags, unsigned long flags)
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{
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@ -217,5 +217,6 @@ struct prctl_mm_map {
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# define PR_SPEC_PRCTL (1UL << 0)
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# define PR_SPEC_ENABLE (1UL << 1)
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# define PR_SPEC_DISABLE (1UL << 2)
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# define PR_SPEC_FORCE_DISABLE (1UL << 3)
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#endif /* _LINUX_PRCTL_H */
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