[PATCH 4.4 070/107] seccomp: Enable speculation flaw mitigations
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2018-07-23 12:47:37
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4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kees Cook <redacted> 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 <redacted> Signed-off-by: Thomas Gleixner <redacted> Signed-off-by: David Woodhouse <redacted> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Srivatsa S. Bhat <redacted> Reviewed-by: Matt Helsley (VMware) <redacted> Reviewed-by: Alexey Makhalov <redacted> Reviewed-by: Bo Gan <redacted> 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); }