4.14-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: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/seccomp.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
--- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -19,6 +19,8 @@ #include <linux/compat.h> #include <linux/coredump.h> #include <linux/kmemleak.h> +#include <linux/nospec.h> +#include <linux/prctl.h> #include <linux/sched.h> #include <linux/sched/task_stack.h> #include <linux/seccomp.h> @@ -227,6 +229,19 @@ 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) { @@ -238,6 +253,8 @@ 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); }