nospec: Allow getting/setting on non-current task

Adjust arch_prctl_get/set_spec_ctrl() to operate on tasks other than
current.

This is needed both for /proc/$pid/status queries and for seccomp (since
thread-syncing can trigger seccomp in non-current threads).

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 16 insertions, 11 deletions

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fc9187b6fae7..e3afb610f2ad 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -530,31 +530,35 @@ static void ssb_select_mitigation()
 
 #undef pr_fmt
 
-static int ssb_prctl_set(unsigned long ctrl)
+static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
 {
-	bool rds = !!test_tsk_thread_flag(current, TIF_RDS);
+	bool rds = !!test_tsk_thread_flag(task, TIF_RDS);
 
 	if (ssb_mode != SPEC_STORE_BYPASS_PRCTL)
 		return -ENXIO;
 
 	if (ctrl == PR_SPEC_ENABLE)
-		clear_tsk_thread_flag(current, TIF_RDS);
+		clear_tsk_thread_flag(task, TIF_RDS);
 	else
-		set_tsk_thread_flag(current, TIF_RDS);
+		set_tsk_thread_flag(task, TIF_RDS);
 
-	if (rds != !!test_tsk_thread_flag(current, TIF_RDS))
+	/*
+	 * If being set on non-current task, delay setting the CPU
+	 * mitigation until it is next scheduled.
+	 */
+	if (task == current && rds != !!test_tsk_thread_flag(task, TIF_RDS))
 		speculative_store_bypass_update();
 
 	return 0;
 }
 
-static int ssb_prctl_get(void)
+static int ssb_prctl_get(struct task_struct *task)
 {
 	switch (ssb_mode) {
 	case SPEC_STORE_BYPASS_DISABLE:
 		return PR_SPEC_DISABLE;
 	case SPEC_STORE_BYPASS_PRCTL:
-		if (test_tsk_thread_flag(current, TIF_RDS))
+		if (test_tsk_thread_flag(task, TIF_RDS))
 			return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
 		return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
 	default:
@@ -564,24 +568,25 @@ static int ssb_prctl_get(void)
 	}
 }
 
-int arch_prctl_spec_ctrl_set(unsigned long which, unsigned long ctrl)
+int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
+			     unsigned long ctrl)
 {
 	if (ctrl != PR_SPEC_ENABLE && ctrl != PR_SPEC_DISABLE)
 		return -ERANGE;
 
 	switch (which) {
 	case PR_SPEC_STORE_BYPASS:
-		return ssb_prctl_set(ctrl);
+		return ssb_prctl_set(task, ctrl);
 	default:
 		return -ENODEV;
 	}
 }
 
-int arch_prctl_spec_ctrl_get(unsigned long which)
+int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 {
 	switch (which) {
 	case PR_SPEC_STORE_BYPASS:
-		return ssb_prctl_get();
+		return ssb_prctl_get(task);
 	default:
 		return -ENODEV;
 	}