Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86/pti update from Thomas Gleixner:
 "Just a single change from the anti-performance departement:

   - Add a new PR_SPEC_DISABLE_NOEXEC option which allows to apply the
     speculation protections on a process without inheriting the state
     on exec.

     This remedies a situation where a Java-launcher has speculation
     protections enabled because that's the default for JVMs which
     causes the launched regular harmless processes to inherit the
     protection state which results in unintended performance
     degradation"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation: Add PR_SPEC_DISABLE_NOEXEC

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 90ae0ca51083..58ac7be52c7a 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -255,6 +255,18 @@ void arch_setup_new_exec(void)
         /* If cpuid was previously disabled for this task, re-enable it. */
         if (test_thread_flag(TIF_NOCPUID))
                 enable_cpuid();
+
+        /*
+         * Don't inherit TIF_SSBD across exec boundary when
+         * PR_SPEC_DISABLE_NOEXEC is used.
+         */
+        if (test_thread_flag(TIF_SSBD) &&
+            task_spec_ssb_noexec(current)) {
+                clear_thread_flag(TIF_SSBD);
+                task_clear_spec_ssb_disable(current);
+                task_clear_spec_ssb_noexec(current);
+                speculation_ctrl_update(task_thread_info(current)->flags);
+        }
 }
 
 static inline void switch_to_bitmap(struct thread_struct *prev,