[RFC PATCH v2 24/24] unwind_user/eh_frame: Add prctl() interface for (un)registering .eh_frame_hdr sections

[Jens Remus <jremus@linux.ibm.com>]

The kernel does not have direct visibility to the ELF contents of
shared libraries.  Add prctl() interfaces to register and unregister
.eh_frame_hdr sections that allow dynamic linkers to tell the kernel
where to find these.

Both prctl's take a pointer to a new structure:

  struct eh_frame_setup {
	__u64	eh_frame_hdr_start;
	__u64	eh_frame_hdr_size;
	__u64	text_start;
	__u64	text_size;
  };

and a size of the passed in structure.  If the prctl's need to be
extended, then the structure could be changes and the sizre of that
structure will tell the kernel what it is the new version.  If the
kernel does not recognize the structure, it returns -EINVAL.

  eh_frame_hdr_start - Virtual address of the .eh_frame_hdr section
  eh_frame_hdr_size  - Length of the .eh_frame_hdr section
  text_start         - Virtual address of the related text section
  text_size          - Length of the related text section

The unregister only needs the eh_frame_hdr_start and requires all of
the remaining fields to be zero.

Based on Steven's patch "[PATCH v2] unwind: Add sframe_(un)register()
system calls". [1]

[1]: https://lore.kernel.org/all/20260528151023.00f5ec4e@gandalf.local.home/

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in RFC v2:
    - eh_frame_{register|unregister}(): Reject zero user_data or size.

 include/linux/eh_frame.h      | 20 +++++++++++++++
 include/uapi/linux/eh_frame.h | 14 +++++++++++
 include/uapi/linux/prctl.h    |  4 +++
 kernel/sys.c                  | 11 +++++++++
 kernel/unwind/eh_frame.c      | 46 +++++++++++++++++++++++++++++++++++
 5 files changed, 95 insertions(+)
 create mode 100644 include/uapi/linux/eh_frame.h

diff --git a/include/linux/eh_frame.h b/include/linux/eh_frame.h
index 3c88ab2f7858..3a61ed0ae739 100644
--- a/include/linux/eh_frame.h
+++ b/include/linux/eh_frame.h
@@ -6,6 +6,8 @@
 #include <linux/srcu.h>
 #include <linux/unwind_user_types.h>
 
+struct eh_frame_setup;
+
 #ifdef CONFIG_HAVE_UNWIND_USER_EH_FRAME
 
 struct eh_frame_section {
@@ -40,6 +42,12 @@ extern int eh_frame_add_section(unsigned long eh_frame_hdr_start,
 				unsigned long text_start,
 				unsigned long text_end);
 extern int eh_frame_remove_section(unsigned long eh_frame_hdr_start);
+
+extern int eh_frame_register(struct eh_frame_setup __user *user_data,
+			     __kernel_size_t size);
+extern int eh_frame_unregister(struct eh_frame_setup __user *user_data,
+			       __kernel_size_t size);
+
 extern int eh_frame_find(unsigned long ip, struct unwind_user_frame *frame);
 
 static inline bool current_has_eh_frame(void)
@@ -78,6 +86,18 @@ static inline int eh_frame_find(unsigned long ip, struct unwind_user_frame *fram
 	return -ENOSYS;
 }
 
+static inline int eh_frame_register(struct eh_frame_setup __user *user_data,
+				    __kernel_size_t size)
+{
+	return -EINVAL;
+}
+
+static inline int eh_frame_unregister(struct eh_frame_setup __user *user_data,
+				      __kernel_size_t size)
+{
+	return -EINVAL;
+}
+
 static inline bool current_has_eh_frame(void) { return false; }
 
 #endif /* CONFIG_HAVE_UNWIND_USER_EH_FRAME */
diff --git a/include/uapi/linux/eh_frame.h b/include/uapi/linux/eh_frame.h
new file mode 100644
index 000000000000..8cca3792f323
--- /dev/null
+++ b/include/uapi/linux/eh_frame.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_EH_FRAME_H
+#define _UAPI_LINUX_EH_FRAME_H
+
+#include <linux/types.h>
+
+struct eh_frame_setup {
+	__u64	eh_frame_hdr_start;
+	__u64	eh_frame_hdr_size;
+	__u64	text_start;
+	__u64	text_size;
+};
+
+#endif /* _UAPI_LINUX_EH_FRAME_H */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index b6ec6f693719..801a209bab3f 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -416,4 +416,8 @@ struct prctl_mm_map {
 # define PR_CFI_DISABLE		_BITUL(1)
 # define PR_CFI_LOCK		_BITUL(2)
 
+/* EH_FRAME management */
+#define PR_REGISTER_EH_FRAME		82
+#define PR_UNREGISTER_EH_FRAME		83
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index df69bd71de03..ee67badf267c 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/eh_frame.h>
 
 #include <linux/nospec.h>
 
@@ -2907,6 +2908,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		if (arg3 & PR_CFI_LOCK && !(arg3 & PR_CFI_DISABLE))
 			error = arch_prctl_lock_branch_landing_pad_state(me);
 		break;
+	case PR_REGISTER_EH_FRAME:
+		if (arg4 || arg5)
+			return -EINVAL;
+		error = eh_frame_register((void __user *)arg2, arg3);
+		break;
+	case PR_UNREGISTER_EH_FRAME:
+		if (arg4 || arg5)
+			return -EINVAL;
+		error = eh_frame_unregister((void __user *)arg2, arg3);
+		break;
 	default:
 		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
 		error = -EINVAL;
diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c
index d1656f5d40f1..063133d1bf97 100644
--- a/kernel/unwind/eh_frame.c
+++ b/kernel/unwind/eh_frame.c
@@ -15,6 +15,7 @@
 #include <linux/types.h>
 #include <linux/unwind_user_types.h>
 #include <linux/unwind_user_eh_frame_types.h>
+#include <uapi/linux/eh_frame.h>
 
 #include "eh_frame.h"
 #include "eh_frame_debug.h"
@@ -1609,3 +1610,48 @@ void eh_frame_free_mm(struct mm_struct *mm)
 
 	mtree_destroy(&mm->eh_frame_mt);
 }
+
+int eh_frame_register(struct eh_frame_setup __user *user_data, __kernel_size_t size)
+{
+	struct eh_frame_setup data;
+	unsigned long eh_frame_hdr_end, text_end;
+
+	if (!user_data || !size)
+		return -EINVAL;
+
+	if (size != sizeof(data))
+		return -EINVAL;
+
+	if (copy_from_user(&data, user_data, sizeof(data)))
+		return -EFAULT;
+
+	if (check_add_overflow(data.eh_frame_hdr_start, data.eh_frame_hdr_size,
+			       &eh_frame_hdr_end))
+		return -EINVAL;
+
+	if (check_add_overflow(data.text_start, data.text_size, &text_end))
+		return -EINVAL;
+
+	return eh_frame_add_section(data.eh_frame_hdr_start, eh_frame_hdr_end,
+				    data.text_start, text_end);
+}
+
+int eh_frame_unregister(struct eh_frame_setup __user *user_data, __kernel_size_t size)
+{
+	struct eh_frame_setup data;
+
+	if (!user_data || !size)
+		return -EINVAL;
+
+	if (size != sizeof(data))
+		return -EINVAL;
+
+	if (copy_from_user(&data, user_data, sizeof(data)))
+		return -EFAULT;
+
+	/* Unregister only uses eh_frame_hdr_start */
+	if (data.eh_frame_hdr_size || data.text_start || data.text_size)
+		return -EINVAL;
+
+	return eh_frame_remove_section(data.eh_frame_hdr_start);
+}
-- 
2.53.0