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

2 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 01874d54f4fd..2da82eff0eb4 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -798,15 +798,25 @@ static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
 		if (task_spec_ssb_force_disable(task))
 			return -EPERM;
 		task_clear_spec_ssb_disable(task);
+		task_clear_spec_ssb_noexec(task);
 		task_update_spec_tif(task);
 		break;
 	case PR_SPEC_DISABLE:
 		task_set_spec_ssb_disable(task);
+		task_clear_spec_ssb_noexec(task);
 		task_update_spec_tif(task);
 		break;
 	case PR_SPEC_FORCE_DISABLE:
 		task_set_spec_ssb_disable(task);
 		task_set_spec_ssb_force_disable(task);
+		task_clear_spec_ssb_noexec(task);
+		task_update_spec_tif(task);
+		break;
+	case PR_SPEC_DISABLE_NOEXEC:
+		if (task_spec_ssb_force_disable(task))
+			return -EPERM;
+		task_set_spec_ssb_disable(task);
+		task_set_spec_ssb_noexec(task);
 		task_update_spec_tif(task);
 		break;
 	default:
@@ -885,6 +895,8 @@ static int ssb_prctl_get(struct task_struct *task)
 	case SPEC_STORE_BYPASS_PRCTL:
 		if (task_spec_ssb_force_disable(task))
 			return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
+		if (task_spec_ssb_noexec(task))
+			return PR_SPEC_PRCTL | PR_SPEC_DISABLE_NOEXEC;
 		if (task_spec_ssb_disable(task))
 			return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
 		return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
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,