Implement ptrace getter/setter interface for syscall user dispatch.

These prctl settings are presently write-only, making it impossible to
implement transparent checkpoint via software like CRIU.

This is modeled after a similar interface for SECCOMP, which can have
its configuration dumped by ptrace.

Signed-off-by: Gregory Price <gregory.price@memverge.com>
---
 .../admin-guide/syscall-user-dispatch.rst     |  5 ++-
 include/linux/syscall_user_dispatch.h         | 19 +++++++++
 include/uapi/linux/ptrace.h                   |  9 +++++
 kernel/entry/syscall_user_dispatch.c          | 40 +++++++++++++++++++
 kernel/ptrace.c                               |  9 +++++
 5 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/syscall-user-dispatch.rst b/Documentation/admin-guide/syscall-user-dispatch.rst
index 60314953c728..a23ae21a1d5b 100644
--- a/Documentation/admin-guide/syscall-user-dispatch.rst
+++ b/Documentation/admin-guide/syscall-user-dispatch.rst
@@ -43,7 +43,10 @@ doesn't rely on any of the syscall ABI to make the filtering.  It uses
 only the syscall dispatcher address and the userspace key.
 
 As the ABI of these intercepted syscalls is unknown to Linux, these
-syscalls are not instrumentable via ptrace or the syscall tracepoints.
+syscalls are not instrumentable via ptrace or the syscall tracepoints,
+however an interfaces to suspend, checkpoint, and restore syscall user
+dispatch configuration has been added to ptrace to assist userland
+checkpoint/restart software.
 
 Interface
 ---------
diff --git a/include/linux/syscall_user_dispatch.h b/include/linux/syscall_user_dispatch.h
index a0ae443fb7df..9e1bd0d87c1e 100644
--- a/include/linux/syscall_user_dispatch.h
+++ b/include/linux/syscall_user_dispatch.h
@@ -22,6 +22,13 @@ int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
 #define clear_syscall_work_syscall_user_dispatch(tsk) \
 	clear_task_syscall_work(tsk, SYSCALL_USER_DISPATCH)
 
+int syscall_user_dispatch_get_config(struct task_struct *task, unsigned long size,
+	void __user *data);
+
+int syscall_user_dispatch_set_config(struct task_struct *task, unsigned long size,
+	void __user *data);
+
+
 #else
 struct syscall_user_dispatch {};
 
@@ -35,6 +42,18 @@ static inline void clear_syscall_work_syscall_user_dispatch(struct task_struct *
 {
 }
 
+static inline int syscall_user_dispatch_get_config(struct task_struct *task, unsigned long size,
+	void __user *data)
+{
+	return -EINVAL;
+}
+
+static inline int syscall_user_dispatch_set_config(struct task_struct *task, unsigned long size,
+	void __user *data)
+{
+	return -EINVAL;
+}
+
 #endif /* CONFIG_GENERIC_ENTRY */
 
 #endif /* _SYSCALL_USER_DISPATCH_H */
diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index ba9e3f19a22c..53ef59134dcb 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -112,6 +112,15 @@ struct ptrace_rseq_configuration {
 	__u32 pad;
 };
 
+#define PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG 0x4210
+#define PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG 0x4211
+struct syscall_user_dispatch_config {
+	__u64 mode;
+	__s8 *selector;
+	__u64 offset;
+	__u64 len;
+};
+
 /*
  * These values are stored in task->ptrace_message
  * by ptrace_stop to describe the current syscall-stop.
diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c
index b5ec75164805..ee02ce21f75e 100644
--- a/kernel/entry/syscall_user_dispatch.c
+++ b/kernel/entry/syscall_user_dispatch.c
@@ -111,3 +111,43 @@ int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
 
 	return 0;
 }
+
+int syscall_user_dispatch_get_config(struct task_struct *task, unsigned long size,
+		void __user *data)
+{
+	struct syscall_user_dispatch *sd = &task->syscall_dispatch;
+	struct syscall_user_dispatch_config config;
+
+	if (size != sizeof(struct syscall_user_dispatch_config))
+		return -EINVAL;
+
+	if (test_syscall_work(SYSCALL_USER_DISPATCH))
+		config.mode = PR_SYS_DISPATCH_ON;
+	else
+		config.mode = PR_SYS_DISPATCH_OFF;
+
+	config.offset = sd->offset;
+	config.len = sd->len;
+	config.selector = sd->selector;
+
+	if (copy_to_user(data, &config, sizeof(config)))
+		return -EFAULT;
+
+	return 0;
+}
+
+int syscall_user_dispatch_set_config(struct task_struct *task, unsigned long size,
+		void __user *data)
+{
+	struct syscall_user_dispatch_config config;
+	int ret;
+
+	if (size != sizeof(struct syscall_user_dispatch_config))
+		return -EINVAL;
+
+	if (copy_from_user(&config, data, sizeof(config)))
+		return -EFAULT;
+
+	return set_syscall_user_dispatch(config.mode, config.offset, config.len,
+			config.selector);
+}
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index a348b68d07a2..76de46e080e2 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -32,6 +32,7 @@
 #include <linux/compat.h>
 #include <linux/sched/signal.h>
 #include <linux/minmax.h>
+#include <linux/syscall_user_dispatch.h>
 
 #include <asm/syscall.h>	/* for syscall_get_* */
 
@@ -1263,6 +1264,14 @@ int ptrace_request(struct task_struct *child, long request,
 		break;
 #endif
 
+	case PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG:
+		ret = syscall_user_dispatch_set_config(child, addr, datavp);
+		break;
+
+	case PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG:
+		ret = syscall_user_dispatch_get_config(child, addr, datavp);
+		break;
+
 	default:
 		break;
 	}
-- 
2.39.0

Hi Gregory,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[cannot apply to tip/core/entry]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Gregory-Price/ptrace-syscall_user_dispatch-add-a-getter-setter-for-sud-configuration/20230125-115155
patch link:    https://lore.kernel.org/r/20230125025126.787431-3-gregory.price%40memverge.com
patch subject: [PATCH v6 2/2] ptrace,syscall_user_dispatch: add a getter/setter for sud configuration
config: x86_64-allyesconfig (https://download.01.org/0day-ci/archive/20230125/202301251548.C0OCmAX0-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/581ad4d3309b94aafb967b0ca56607436c18127f
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Gregory-Price/ptrace-syscall_user_dispatch-add-a-getter-setter-for-sud-configuration/20230125-115155
        git checkout 581ad4d3309b94aafb967b0ca56607436c18127f
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   kernel/entry/syscall_user_dispatch.c: In function 'syscall_user_dispatch_set_config':
>> kernel/entry/syscall_user_dispatch.c:143:13: warning: unused variable 'ret' [-Wunused-variable]
     143 |         int ret;
         |             ^~~


vim +/ret +143 kernel/entry/syscall_user_dispatch.c

   138	
   139	int syscall_user_dispatch_set_config(struct task_struct *task, unsigned long size,
   140			void __user *data)
   141	{
   142		struct syscall_user_dispatch_config config;
 > 143		int ret;

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests