[tip: x86/shstk] x86: Expose thread features in /proc/$PID/status

[tip-bot2 for Rick Edgecombe]

The following commit has been merged into the x86/shstk branch of tip:

Commit-ID:     214b23e1186488ff68feb74d8561286a5c83b281
Gitweb:        https://git.kernel.org/tip/214b23e1186488ff68feb74d8561286a5c83b281
Author:        Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
AuthorDate:    Sat, 18 Mar 2023 17:15:30 -07:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Mon, 20 Mar 2023 09:01:12 -07:00

x86: Expose thread features in /proc/$PID/status

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.

[Switched to CET, added to commit log]

Co-developed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Tested-by: John Allen <john.allen@xxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20230319001535.23210-36-rick.p.edgecombe%40intel.com
---
 arch/x86/kernel/cpu/proc.c | 23 +++++++++++++++++++++++
 fs/proc/array.c            |  6 ++++++
 include/linux/proc_fs.h    |  2 ++
 3 files changed, 31 insertions(+)

diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 099b6f0..31c0e68 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 9b0315d..3e1a33d 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -423,6 +423,11 @@ static inline void task_thp_status(struct seq_file *m, struct mm_struct *mm)
 	seq_printf(m, "THP_enabled:\t%d\n", thp_enabled);
 }
 
+__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)
 {
@@ -446,6 +451,7 @@ 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 0260f5e..80ff8e5 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)