When a task changes its dumpability, arch_update_spec_ctrl_restriction() is called to place restriction on the task's speculative execution according to dumpability changes.
Implements arch_update_spec_restriction() for x86. Use STIBP to restrict speculative execution when running a task set to non-dumpable, or clear the restriction if the task is set to dumpable.
Signed-off-by: Tim Chen tim.c.chen@linux.intel.com --- Documentation/admin-guide/kernel-parameters.txt | 3 ++- arch/x86/kernel/cpu/bugs.c | 23 ++++++++++++++++++++--- 2 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 89b193c..3979b12 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4229,7 +4229,8 @@ If the CPU is vulnerable, the default mitigation is architecture and Kconfig dependent. See below. prctl - Enable mitigations per thread by restricting - indirect branch speculation via prctl. + indirect branch speculation via prctl or setting + the thread as non-dumpable. Mitigation for a thread is not enabled by default to avoid mitigation overhead. The state of of the control is inherited on fork. diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index f349b3f..6cd64445 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/coredump.h>
#include <asm/spec-ctrl.h> #include <asm/cmdline.h> @@ -153,8 +154,8 @@ static const char *spectre_v2_strings[] = { static const char *spectre_v2_app2app_strings[] = { [SPECTRE_V2_APP2APP_NONE] = "App-App Vulnerable", [SPECTRE_V2_APP2APP_STRICT] = "App-App Mitigation: Full app to app attack protection", - [SPECTRE_V2_APP2APP_PRCTL] = "App-App Mitigation: Protect branch speculation restricted tasks", - [SPECTRE_V2_APP2APP_SECCOMP] = "App-App Mitigation: Protect branch speculation restricted and seccomp tasks", + [SPECTRE_V2_APP2APP_PRCTL] = "App-App Mitigation: Protect non-dumpable and branch speculation restricted tasks", + [SPECTRE_V2_APP2APP_SECCOMP] = "App-App Mitigation: Protect non-dumpable, branch speculation restricted and seccomp tasks", };
/* Lightweight mitigation: mitigate only tasks with TIF_SPEC_INDIR_BRANCH */ @@ -792,13 +793,29 @@ static void set_task_restrict_indir_branch(struct task_struct *tsk, bool restric
if (restrict_on) update = !test_and_set_tsk_thread_flag(tsk, TIF_SPEC_INDIR_BRANCH); - else + else if (!task_spec_indir_branch_disable(tsk)) update = test_and_clear_tsk_thread_flag(tsk, TIF_SPEC_INDIR_BRANCH);
if (tsk == current && update) speculation_ctrl_update_current(); }
+int arch_update_spec_restriction(struct task_struct *task) +{ + if (!static_branch_unlikely(&spectre_v2_app_lite)) + return 0; + + if (!task->mm) + return -EINVAL; + + if (get_dumpable(task->mm) != SUID_DUMP_USER) + set_task_restrict_indir_branch(task, true); + else + set_task_restrict_indir_branch(task, false); + + return 0; +} + static int indir_branch_prctl_set(struct task_struct *task, unsigned long ctrl) { switch (ctrl) {