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

Documentation/userspace-api/spec_ctrl.rst

@@ -28,9 +28,9 @@ PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
 which is selected with arg2 of prctl(2). The return value uses bits 0-3 with
 the following meaning:
 
-==== ===================== ===================================================
+==== ====================== ==================================================
 Bit  Define                 Description
-==== ===================== ===================================================
+==== ====================== ==================================================
 0    PR_SPEC_PRCTL          Mitigation can be controlled per task by
                             PR_SET_SPECULATION_CTRL.
 1    PR_SPEC_ENABLE         The speculation feature is enabled, mitigation is
@@ -39,7 +39,9 @@ Bit  Define                Description
                             enabled.
 3    PR_SPEC_FORCE_DISABLE  Same as PR_SPEC_DISABLE, but cannot be undone. A
                             subsequent prctl(..., PR_SPEC_ENABLE) will fail.
-==== ===================== ===================================================
+4    PR_SPEC_DISABLE_NOEXEC Same as PR_SPEC_DISABLE, but the state will be
+                            cleared on :manpage:`execve(2)`.
+==== ====================== ==================================================
 
 If all bits are 0 the CPU is not affected by the speculation misfeature.
 
@@ -92,6 +94,7 @@ Speculation misfeature controls
    * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
    * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
    * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);
+   * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE_NOEXEC, 0, 0);
 
 - PR_SPEC_INDIR_BRANCH: Indirect Branch Speculation in User Processes
                         (Mitigate Spectre V2 style attacks against user processes)

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;

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,

include/linux/sched.h

@@ -1453,6 +1453,7 @@ static inline bool is_percpu_thread(void)
 #define PFA_SPEC_SSB_FORCE_DISABLE	4	/* Speculative Store Bypass force disabled*/
 #define PFA_SPEC_IB_DISABLE		5	/* Indirect branch speculation restricted */
 #define PFA_SPEC_IB_FORCE_DISABLE	6	/* Indirect branch speculation permanently restricted */
+#define PFA_SPEC_SSB_NOEXEC		7	/* Speculative Store Bypass clear on execve() */
 
 #define TASK_PFA_TEST(name, func)					\
 	static inline bool task_##func(struct task_struct *p)		\
@@ -1481,6 +1482,10 @@ TASK_PFA_TEST(SPEC_SSB_DISABLE, spec_ssb_disable)
 TASK_PFA_SET(SPEC_SSB_DISABLE, spec_ssb_disable)
 TASK_PFA_CLEAR(SPEC_SSB_DISABLE, spec_ssb_disable)
 
+TASK_PFA_TEST(SPEC_SSB_NOEXEC, spec_ssb_noexec)
+TASK_PFA_SET(SPEC_SSB_NOEXEC, spec_ssb_noexec)
+TASK_PFA_CLEAR(SPEC_SSB_NOEXEC, spec_ssb_noexec)
+
 TASK_PFA_TEST(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
 TASK_PFA_SET(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
 

include/uapi/linux/prctl.h

@@ -219,6 +219,7 @@ struct prctl_mm_map {
 # define PR_SPEC_ENABLE			(1UL << 1)
 # define PR_SPEC_DISABLE		(1UL << 2)
 # define PR_SPEC_FORCE_DISABLE		(1UL << 3)
+# define PR_SPEC_DISABLE_NOEXEC		(1UL << 4)
 
 /* Reset arm64 pointer authentication keys */
 #define PR_PAC_RESET_KEYS		54

tools/include/uapi/linux/prctl.h

@@ -219,6 +219,7 @@ struct prctl_mm_map {
 # define PR_SPEC_ENABLE			(1UL << 1)
 # define PR_SPEC_DISABLE		(1UL << 2)
 # define PR_SPEC_FORCE_DISABLE		(1UL << 3)
+# define PR_SPEC_DISABLE_NOEXEC		(1UL << 4)
 
 /* Reset arm64 pointer authentication keys */
 #define PR_PAC_RESET_KEYS		54