[Patch v3 12/13] x86/speculation: Protect non-dumpable processes against Spectre v2 attack

[Tim Chen <tim.c.chen@linux.intel.com>]

Mark the non-dumpable processes with TIF_STIBP flag so they will
use STIBP and IBPB defenses against Spectre v2 attack from
processes in user space.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 1d317f2..cc77b9e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/nospec.h>
 #include <linux/prctl.h>
+#include <linux/sched/coredump.h>
 
 #include <asm/spec-ctrl.h>
 #include <asm/cmdline.h>
@@ -773,6 +774,26 @@ int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
 	}
 }
 
+void arch_set_dumpable(struct task_struct *tsk, unsigned int value)
+{
+	bool update;
+
+	if (!static_branch_unlikely(&spectre_v2_app_lite))
+		return;
+	if (!static_cpu_has(X86_FEATURE_STIBP))
+		return;
+	if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE)
+		return;
+
+	if (tsk->mm && value != SUID_DUMP_USER)
+		update = !test_and_set_tsk_thread_flag(tsk, TIF_STIBP);
+	else
+		update = test_and_clear_tsk_thread_flag(tsk, TIF_STIBP);
+
+	if (tsk == current && update)
+		speculation_ctrl_update_current();
+}
+
 #ifdef CONFIG_SECCOMP
 void arch_seccomp_spec_mitigate(struct task_struct *task)
 {
-- 
2.9.4