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Subject[PATCH 4.4 070/107] seccomp: Enable speculation flaw mitigations
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

commit 5c3070890d06ff82eecb808d02d2ca39169533ef upstream

When speculation flaw mitigations are opt-in (via prctl), using seccomp
will automatically opt-in to these protections, since using seccomp
indicates at least some level of sandboxing is desired.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@gmail.com>
Reviewed-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Bo Gan <ganb@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

kernel/seccomp.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -16,6 +16,8 @@
#include <linux/atomic.h>
#include <linux/audit.h>
#include <linux/compat.h>
+#include <linux/nospec.h>
+#include <linux/prctl.h>
#include <linux/sched.h>
#include <linux/seccomp.h>
#include <linux/slab.h>
@@ -214,6 +216,19 @@ static inline bool seccomp_may_assign_mo
return true;
}

+/*
+ * If a given speculation mitigation is opt-in (prctl()-controlled),
+ * select it, by disabling speculation (enabling mitigation).
+ */
+static inline void spec_mitigate(struct task_struct *task,
+ unsigned long which)
+{
+ int state = arch_prctl_spec_ctrl_get(task, which);
+
+ if (state > 0 && (state & PR_SPEC_PRCTL))
+ arch_prctl_spec_ctrl_set(task, which, PR_SPEC_DISABLE);
+}
+
static inline void seccomp_assign_mode(struct task_struct *task,
unsigned long seccomp_mode)
{
@@ -225,6 +240,8 @@ static inline void seccomp_assign_mode(s
* filter) is set.
*/
smp_mb__before_atomic();
+ /* Assume seccomp processes want speculation flaw mitigation. */
+ spec_mitigate(task, PR_SPEC_STORE_BYPASS);
set_tsk_thread_flag(task, TIF_SECCOMP);
}


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