[PATCH 4.9 59/87] prctl: Add force disable speculation
From: Greg Kroah-Hartman
Date: Mon May 21 2018 - 17:24:12 EST
4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit 356e4bfff2c5489e016fdb925adbf12a1e3950ee upstream
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@xxxxxxxxxxxxx>
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
Documentation/spec_ctrl.txt | 34 +++++++++++++++++++++-------------
arch/x86/kernel/cpu/bugs.c | 35 +++++++++++++++++++++++++----------
fs/proc/array.c | 3 +++
include/linux/sched.h | 9 +++++++++
include/uapi/linux/prctl.h | 1 +
5 files changed, 59 insertions(+), 23 deletions(-)
--- a/Documentation/spec_ctrl.txt
+++ b/Documentation/spec_ctrl.txt
@@ -25,19 +25,21 @@ PR_GET_SPECULATION_CTRL
-----------------------
PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
-which is selected with arg2 of prctl(2). The return value uses bits 0-2 with
+which is selected with arg2 of prctl(2). The return value uses bits 0-3 with
the following meaning:
-==== ================ ===================================================
-Bit Define Description
-==== ================ ===================================================
-0 PR_SPEC_PRCTL Mitigation can be controlled per task by
- PR_SET_SPECULATION_CTRL
-1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
- disabled
-2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
- enabled
-==== ================ ===================================================
+==== ===================== ===================================================
+Bit Define Description
+==== ===================== ===================================================
+0 PR_SPEC_PRCTL Mitigation can be controlled per task by
+ PR_SET_SPECULATION_CTRL
+1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
+ disabled
+2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
+ enabled
+3 PR_SPEC_FORCE_DISABLE Same as PR_SPEC_DISABLE, but cannot be undone. A
+ subsequent prctl(..., PR_SPEC_ENABLE) will fail.
+==== ===================== ===================================================
If all bits are 0 the CPU is not affected by the speculation misfeature.
@@ -47,9 +49,11 @@ misfeature will fail.
PR_SET_SPECULATION_CTRL
-----------------------
+
PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which
is selected by arg2 of :manpage:`prctl(2)` per task. arg3 is used to hand
-in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE.
+in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE or
+PR_SPEC_FORCE_DISABLE.
Common error codes
------------------
@@ -70,10 +74,13 @@ Value Meaning
0 Success
ERANGE arg3 is incorrect, i.e. it's neither PR_SPEC_ENABLE nor
- PR_SPEC_DISABLE
+ PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE
ENXIO Control of the selected speculation misfeature is not possible.
See PR_GET_SPECULATION_CTRL.
+
+EPERM Speculation was disabled with PR_SPEC_FORCE_DISABLE and caller
+ tried to enable it again.
======= =================================================================
Speculation misfeature controls
@@ -84,3 +91,4 @@ Speculation misfeature controls
* prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, 0, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
+ * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -532,21 +532,37 @@ 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;
@@ -558,7 +574,9 @@ static int ssb_prctl_get(struct task_str
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:
@@ -571,9 +589,6 @@ static int ssb_prctl_get(struct task_str
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);
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -355,6 +355,9 @@ static inline void task_seccomp(struct s
case PR_SPEC_NOT_AFFECTED:
seq_printf(m, "not vulnerable");
break;
+ case PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE:
+ seq_printf(m, "thread force mitigated");
+ break;
case PR_SPEC_PRCTL | PR_SPEC_DISABLE:
seq_printf(m, "thread mitigated");
break;
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2354,6 +2354,8 @@ static inline void memalloc_noio_restore
#define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */
#define PFA_SPREAD_SLAB 2 /* Spread some slab caches over cpuset */
#define PFA_LMK_WAITING 3 /* Lowmemorykiller is waiting */
+#define PFA_SPEC_SSB_DISABLE 4 /* Speculative Store Bypass disabled */
+#define PFA_SPEC_SSB_FORCE_DISABLE 5 /* Speculative Store Bypass force disabled*/
#define TASK_PFA_TEST(name, func) \
@@ -2380,6 +2382,13 @@ TASK_PFA_CLEAR(SPREAD_SLAB, spread_slab)
TASK_PFA_TEST(LMK_WAITING, lmk_waiting)
TASK_PFA_SET(LMK_WAITING, lmk_waiting)
+TASK_PFA_TEST(SPEC_SSB_DISABLE, spec_ssb_disable)
+TASK_PFA_SET(SPEC_SSB_DISABLE, spec_ssb_disable)
+TASK_PFA_CLEAR(SPEC_SSB_DISABLE, spec_ssb_disable)
+
+TASK_PFA_TEST(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
+TASK_PFA_SET(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
+
/*
* task->jobctl flags
*/
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -207,5 +207,6 @@ struct prctl_mm_map {
# define PR_SPEC_PRCTL (1UL << 0)
# define PR_SPEC_ENABLE (1UL << 1)
# define PR_SPEC_DISABLE (1UL << 2)
+# define PR_SPEC_FORCE_DISABLE (1UL << 3)
#endif /* _LINUX_PRCTL_H */