[Patch v5 12/16] x86/speculation: Create PRCTL interface to restrict indirect branch speculation
From: Tim Chen
Date: Fri Nov 16 2018 - 21:28:15 EST
Create PRCTL interface to restrict an application's indirect branch
speculation. This will protect the application against spectre v2 attack
from another application.
Invocations:
Check indirect branch speculation status with
- prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, 0, 0, 0);
Enable indirect branch speculation with
- prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
Disable indirect branch speculation with
- prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0);
Force disable indirect branch speculation with
- prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);
See Documentation/userspace-api/spec_ctrl.rst.
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
Documentation/userspace-api/spec_ctrl.rst | 9 ++++
arch/x86/kernel/cpu/bugs.c | 80 +++++++++++++++++++++++++++++++
include/linux/sched.h | 9 ++++
include/uapi/linux/prctl.h | 1 +
tools/include/uapi/linux/prctl.h | 1 +
5 files changed, 100 insertions(+)
diff --git a/Documentation/userspace-api/spec_ctrl.rst b/Documentation/userspace-api/spec_ctrl.rst
index 32f3d55..8a4e268 100644
--- a/Documentation/userspace-api/spec_ctrl.rst
+++ b/Documentation/userspace-api/spec_ctrl.rst
@@ -92,3 +92,12 @@ Speculation misfeature controls
* 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);
+
+- PR_SPEC_INDIR_BRANCH: Indirect Branch Speculation in User Processes
+ (Mitigate Spectre V2 style attacks against user processes)
+
+ Invocations:
+ * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, 0, 0, 0);
+ * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
+ * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0);
+ * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 21caade..8f5187e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -773,12 +773,69 @@ static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
return 0;
}
+static void set_task_stibp(struct task_struct *tsk, bool stibp_on)
+{
+ bool update = false;
+
+ if (stibp_on)
+ update = !test_and_set_tsk_thread_flag(tsk, TIF_STIBP);
+ else
+ update = test_and_clear_tsk_thread_flag(tsk, TIF_STIBP);
+
+ if (tsk == current && update)
+ speculation_ctrl_update_current();
+}
+
+static int indir_branch_prctl_set(struct task_struct *task, unsigned long ctrl)
+{
+ switch (ctrl) {
+ case PR_SPEC_ENABLE:
+ if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE)
+ return 0;
+ /*
+ * Indirect branch speculation is always disabled in
+ * strict mode.
+ */
+ if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_STRICT)
+ return -EPERM;
+ task_clear_spec_indir_branch_disable(task);
+ set_task_stibp(task, false);
+ break;
+ case PR_SPEC_DISABLE:
+ /*
+ * Indirect branch speculation is always allowed when
+ * mitigation is force disabled.
+ */
+ if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE)
+ return -EPERM;
+ if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_STRICT)
+ return 0;
+ task_set_spec_indir_branch_disable(task);
+ set_task_stibp(task, true);
+ break;
+ case PR_SPEC_FORCE_DISABLE:
+ if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE)
+ return -EPERM;
+ if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_STRICT)
+ return 0;
+ task_set_spec_indir_branch_disable(task);
+ task_set_spec_indir_branch_force_disable(task);
+ set_task_stibp(task, true);
+ break;
+ default:
+ return -ERANGE;
+ }
+ return 0;
+}
+
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
unsigned long ctrl)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_set(task, ctrl);
+ case PR_SPEC_INDIR_BRANCH:
+ return indir_branch_prctl_set(task, ctrl);
default:
return -ENODEV;
}
@@ -811,11 +868,34 @@ static int ssb_prctl_get(struct task_struct *task)
}
}
+static int indir_branch_prctl_get(struct task_struct *task)
+{
+ if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+ return PR_SPEC_NOT_AFFECTED;
+
+ switch (spectre_v2_app2app_enabled) {
+ case SPECTRE_V2_APP2APP_NONE:
+ return PR_SPEC_ENABLE;
+ case SPECTRE_V2_APP2APP_LITE:
+ if (task_spec_indir_branch_force_disable(task))
+ return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
+ if (test_tsk_thread_flag(task, TIF_STIBP))
+ return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
+ return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
+ case SPECTRE_V2_APP2APP_STRICT:
+ return PR_SPEC_DISABLE;
+ default:
+ return PR_SPEC_NOT_AFFECTED;
+ }
+}
+
int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_get(task);
+ case PR_SPEC_INDIR_BRANCH:
+ return indir_branch_prctl_get(task);
default:
return -ENODEV;
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a51c13c..e92e4bf 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1453,6 +1453,8 @@ static inline bool is_percpu_thread(void)
#define PFA_SPREAD_SLAB 2 /* Spread some slab caches over cpuset */
#define PFA_SPEC_SSB_DISABLE 3 /* Speculative Store Bypass disabled */
#define PFA_SPEC_SSB_FORCE_DISABLE 4 /* Speculative Store Bypass force disabled*/
+#define PFA_SPEC_INDIR_BRANCH_DISABLE 5 /* Indirect branch speculation restricted in apps */
+#define PFA_SPEC_INDIR_BRANCH_FORCE_DISABLE 6 /* Indirect branch speculation restricted in apps forced */
#define TASK_PFA_TEST(name, func) \
static inline bool task_##func(struct task_struct *p) \
@@ -1484,6 +1486,13 @@ 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_PFA_TEST(SPEC_INDIR_BRANCH_DISABLE, spec_indir_branch_disable)
+TASK_PFA_SET(SPEC_INDIR_BRANCH_DISABLE, spec_indir_branch_disable)
+TASK_PFA_CLEAR(SPEC_INDIR_BRANCH_DISABLE, spec_indir_branch_disable)
+
+TASK_PFA_TEST(SPEC_INDIR_BRANCH_FORCE_DISABLE, spec_indir_branch_force_disable)
+TASK_PFA_SET(SPEC_INDIR_BRANCH_FORCE_DISABLE, spec_indir_branch_force_disable)
+
static inline void
current_restore_flags(unsigned long orig_flags, unsigned long flags)
{
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index c0d7ea0..577f2ca 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -212,6 +212,7 @@ struct prctl_mm_map {
#define PR_SET_SPECULATION_CTRL 53
/* Speculation control variants */
# define PR_SPEC_STORE_BYPASS 0
+# define PR_SPEC_INDIR_BRANCH 1
/* Return and control values for PR_SET/GET_SPECULATION_CTRL */
# define PR_SPEC_NOT_AFFECTED 0
# define PR_SPEC_PRCTL (1UL << 0)
diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
index c0d7ea0..577f2ca 100644
--- a/tools/include/uapi/linux/prctl.h
+++ b/tools/include/uapi/linux/prctl.h
@@ -212,6 +212,7 @@ struct prctl_mm_map {
#define PR_SET_SPECULATION_CTRL 53
/* Speculation control variants */
# define PR_SPEC_STORE_BYPASS 0
+# define PR_SPEC_INDIR_BRANCH 1
/* Return and control values for PR_SET/GET_SPECULATION_CTRL */
# define PR_SPEC_NOT_AFFECTED 0
# define PR_SPEC_PRCTL (1UL << 0)
--
2.9.4