diff mbox series

[v4,32/39] x86: Expose thread features in /proc/$PID/status

Message ID 20221203003606.6838-33-rick.p.edgecombe@intel.com (mailing list archive)
State New
Headers show
Series Shadow stacks for userspace | expand

Commit Message

Rick Edgecombe Dec. 3, 2022, 12:35 a.m. UTC 
Applications and loaders can have logic to decide whether to enable
shadow stack. They usually don't report whether shadow stack has been
enabled or not, so there is no way to verify whether an application
actually is protected by shadow stack.

Add two lines in /proc/$PID/status to report enabled and locked features.

Since, this involves referring to arch specific defines in asm/prctl.h,
implement an arch breakout to emit the feature lines.

Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
[Switched to CET, added to commit log]
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---

v4:
 - Remove "CET" references

v3:
 - Move to /proc/pid/status (Kees)

v2:
 - New patch

 arch/x86/kernel/cpu/proc.c | 23 +++++++++++++++++++++++
 fs/proc/array.c            |  6 ++++++
 include/linux/proc_fs.h    |  2 ++
 3 files changed, 31 insertions(+)

Comments

Kees Cook Dec. 3, 2022, 2:52 a.m. UTC | #1 
On Fri, Dec 02, 2022 at 04:35:59PM -0800, Rick Edgecombe wrote:
> Applications and loaders can have logic to decide whether to enable
> shadow stack. They usually don't report whether shadow stack has been
> enabled or not, so there is no way to verify whether an application
> actually is protected by shadow stack.
> 
> Add two lines in /proc/$PID/status to report enabled and locked features.
> 
> Since, this involves referring to arch specific defines in asm/prctl.h,
> implement an arch breakout to emit the feature lines.
> 
> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> Tested-by: John Allen <john.allen@amd.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Reviewed-by: Kees Cook <keescook@chromium.org>
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 099b6f0d96bd..31c0e68f6227 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -4,6 +4,8 @@ 
 #include <linux/string.h>
 #include <linux/seq_file.h>
 #include <linux/cpufreq.h>
+#include <asm/prctl.h>
+#include <linux/proc_fs.h>
 
 #include "cpu.h"
 
@@ -175,3 +177,24 @@  const struct seq_operations cpuinfo_op = {
 	.stop	= c_stop,
 	.show	= show_cpuinfo,
 };
+
+#ifdef CONFIG_X86_USER_SHADOW_STACK
+static void dump_x86_features(struct seq_file *m, unsigned long features)
+{
+	if (features & ARCH_SHSTK_SHSTK)
+		seq_puts(m, "shstk ");
+	if (features & ARCH_SHSTK_WRSS)
+		seq_puts(m, "wrss ");
+}
+
+void arch_proc_pid_thread_features(struct seq_file *m, struct task_struct *task)
+{
+	seq_puts(m, "x86_Thread_features:\t");
+	dump_x86_features(m, task->thread.features);
+	seq_putc(m, '\n');
+
+	seq_puts(m, "x86_Thread_features_locked:\t");
+	dump_x86_features(m, task->thread.features_locked);
+	seq_putc(m, '\n');
+}
+#endif /* CONFIG_X86_USER_SHADOW_STACK */
diff --git a/fs/proc/array.c b/fs/proc/array.c
index d2a94eafe9a3..96ee17d68b4c 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -433,6 +433,11 @@  static inline void task_untag_mask(struct seq_file *m, struct mm_struct *mm)
 	seq_printf(m, "untag_mask:\t%#lx\n", mm_untag_mask(mm));
 }
 
+__weak void arch_proc_pid_thread_features(struct seq_file *m,
+					  struct task_struct *task)
+{
+}
+
 int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
 			struct pid *pid, struct task_struct *task)
 {
@@ -457,6 +462,7 @@  int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
 	task_cpus_allowed(m, task);
 	cpuset_task_status_allowed(m, task);
 	task_context_switch_counts(m, task);
+	arch_proc_pid_thread_features(m, task);
 	return 0;
 }
 
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 81d6e4ec2294..5a8b21c0a587 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -158,6 +158,8 @@  int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
 			struct pid *pid, struct task_struct *task);
 #endif /* CONFIG_PROC_PID_ARCH_STATUS */
 
+void arch_proc_pid_thread_features(struct seq_file *m, struct task_struct *task);
+
 #else /* CONFIG_PROC_FS */
 
 static inline void proc_root_init(void)