seccomp: Move speculation migitation control to arch code

commit 8bf37d8c067bb7eb8e7c381bdadf9bd89182b6bc upstream

The migitation control is simpler to implement in architecture code as it
avoids the extra function call to check the mode. Aside of that having an
explicit seccomp enabled mode in the architecture mitigations would require
even more workarounds.

Move it into architecture code and provide a weak function in the seccomp
code. Remove the 'which' argument as this allows the architecture to decide
which mitigations are relevant for seccomp.

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>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d6897caa8f47ec437a3b4bbcbc22bd54acd87d00..b005ef721dc7ff6bf5acd7da32b862508b47e531 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -567,6 +567,24 @@ static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
        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);
+       default:
+               return -ENODEV;
+       }
+}
+
+#ifdef CONFIG_SECCOMP
+void arch_seccomp_spec_mitigate(struct task_struct *task)
+{
+       ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
+}
+#endif
+
 static int ssb_prctl_get(struct task_struct *task)
 {
        switch (ssb_mode) {
@@ -585,17 +603,6 @@ static int ssb_prctl_get(struct task_struct *task)
        }
 }
 
-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);
-       default:
-               return -ENODEV;
-       }
-}
-
 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 {
        switch (which) {

diff --git a/include/linux/nospec.h b/include/linux/nospec.h
index a908c954484dab137c8e2d7448f9407076ebd584..0c5ef54fd4162830b55aa676c1ecae4ea6ac23f5 100644 (file)
--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -62,5 +62,7 @@ static inline unsigned long array_index_mask_nospec(unsigned long index,
 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
 int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
                             unsigned long ctrl);
+/* Speculation control for seccomp enforced mitigation */
+void arch_seccomp_spec_mitigate(struct task_struct *task);
 
 #endif /* _LINUX_NOSPEC_H */

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 4bb8a5a5d68a653315f4397f7acb59e7f3f410ae..9a9203b15cdea5ed7916fd6865832c8fcd829a12 100644 (file)
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -216,18 +216,7 @@ static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
        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_FORCE_DISABLE);
-}
+void __weak arch_seccomp_spec_mitigate(struct task_struct *task) { }
 
 static inline void seccomp_assign_mode(struct task_struct *task,
                                       unsigned long seccomp_mode,
@@ -243,7 +232,7 @@ static inline void seccomp_assign_mode(struct task_struct *task,
        smp_mb__before_atomic();
        /* Assume default seccomp processes want spec flaw mitigation. */
        if ((flags & SECCOMP_FILTER_FLAG_SPEC_ALLOW) == 0)
-               spec_mitigate(task, PR_SPEC_STORE_BYPASS);
+               arch_seccomp_spec_mitigate(task);
        set_tsk_thread_flag(task, TIF_SECCOMP);
 }