[PATCH v14 19/19] unwind_user/sframe: Add prctl() interface for registering .sframe sections

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

The kernel doesn't have direct visibility to the ELF contents of shared
libraries.  Add some prctl() interfaces which allow glibc to tell the
kernel where to find .sframe sections.

[
  This adds an interface for prctl() for testing loading of sframes for
  libraries. But this interface should really be a system call. This patch
  is for testing purposes only and should not be applied to mainline.
]

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Reviewed-by: Indu Bhagat <ibhagatgnu@xxxxxxxxx>
Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---

Notes (jremus):
    Changes in v14:
    - Bump PR_ADD_SFRAME and PR_REMOVE_SFRAME.

 include/uapi/linux/prctl.h | 6 +++++-
 kernel/sys.c               | 8 ++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index b6ec6f693719..0aa0ec971843 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -368,7 +368,7 @@ struct prctl_mm_map {
  * configuration.  All bits may be locked via this call, including
  * undefined bits.
  */
-#define PR_LOCK_SHADOW_STACK_STATUS      76
+#define PR_LOCK_SHADOW_STACK_STATUS	76
 
 /*
  * Controls the mode of timer_create() for CRIU restore operations.
@@ -416,4 +416,8 @@ struct prctl_mm_map {
 # define PR_CFI_DISABLE		_BITUL(1)
 # define PR_CFI_LOCK		_BITUL(2)
 
+/* SFRAME management */
+#define PR_ADD_SFRAME			82
+#define PR_REMOVE_SFRAME		83
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 62e842055cc9..6e81e82bc991 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -65,6 +65,7 @@
 #include <linux/rcupdate.h>
 #include <linux/uidgid.h>
 #include <linux/cred.h>
+#include <linux/sframe.h>
 
 #include <linux/nospec.h>
 
@@ -2906,6 +2907,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			break;
 		if (arg3 & PR_CFI_LOCK && !(arg3 & PR_CFI_DISABLE))
 			error = arch_prctl_lock_branch_landing_pad_state(me);
+	case PR_ADD_SFRAME:
+		error = sframe_add_section(arg2, arg3, arg4, arg5);
+		break;
+	case PR_REMOVE_SFRAME:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = sframe_remove_section(arg2);
 		break;
 	default:
 		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
-- 
2.51.0