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    Subject[PATCH 4.16 080/110] seccomp: Enable speculation flaw mitigations
    Date
    4.16-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);
    }


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