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Subject[PATCH v11 2/2] ptrace,syscall_user_dispatch: checkpoint/restore support for SUD
Date
Implement ptrace getter/setter interface for syscall user dispatch.

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

'on_dispatch' field is not exposed because it is a kernel-internal
only field that cannot be 'true' when returning to userland.

Signed-off-by: Gregory Price <gregory.price@memverge.com>
---
.../admin-guide/syscall-user-dispatch.rst | 4 +
include/linux/syscall_user_dispatch.h | 18 +++++
include/uapi/linux/ptrace.h | 30 ++++++++
kernel/entry/syscall_user_dispatch.c | 40 ++++++++++
kernel/ptrace.c | 9 +++
tools/testing/selftests/ptrace/.gitignore | 1 +
tools/testing/selftests/ptrace/Makefile | 2 +-
tools/testing/selftests/ptrace/get_set_sud.c | 77 +++++++++++++++++++
8 files changed, 180 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/ptrace/get_set_sud.c

diff --git a/Documentation/admin-guide/syscall-user-dispatch.rst b/Documentation/admin-guide/syscall-user-dispatch.rst
index 60314953c728..f7648c08297e 100644
--- a/Documentation/admin-guide/syscall-user-dispatch.rst
+++ b/Documentation/admin-guide/syscall-user-dispatch.rst
@@ -73,6 +73,10 @@ thread-wide, without the need to invoke the kernel directly. selector
can be set to SYSCALL_DISPATCH_FILTER_ALLOW or SYSCALL_DISPATCH_FILTER_BLOCK.
Any other value should terminate the program with a SIGSYS.

+Additionally, a task's syscall user dispatch configuration can be peeked
+and poked via the PTRACE_(GET|SET)_SYSCALL_USER_DISPATCH_CONFIG ptrace
+requests. This is useful for checkpoint/restart software.
+
Security Notes
--------------

diff --git a/include/linux/syscall_user_dispatch.h b/include/linux/syscall_user_dispatch.h
index a0ae443fb7df..641ca8880995 100644
--- a/include/linux/syscall_user_dispatch.h
+++ b/include/linux/syscall_user_dispatch.h
@@ -22,6 +22,12 @@ 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 +41,18 @@ 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 195ae64a8c87..033f4db75c60 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -112,6 +112,36 @@ struct ptrace_rseq_configuration {
__u32 pad;
};

+#define PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG 0x4210
+#define PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG 0x4211
+
+/*
+ * struct ptrace_sud_config - Per-task configuration for SUD
+ * @mode: One of PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF
+ * @selector: Tracee's user virtual address of SUD selector
+ * @offset: SUD exclusion area (virtual address)
+ * @len: Length of SUD exclusion area
+ *
+ * Used to get/set the syscall user dispatch configuration for tracee.
+ * process. Selector is optional (may be NULL), and if invalid will produce
+ * a SIGSEGV in the tracee upon first access.
+ *
+ * If mode is PR_SYS_DISPATCH_ON, syscall dispatch will be enabled. If
+ * PR_SYS_DISPATCH_OFF, syscall dispatch will be disabled and all other
+ * parameters must be 0. The value in *selector (if not null), also determines
+ * whether syscall dispatch will occur.
+ *
+ * The SUD Exclusion area described by offset/len is the virtual address space
+ * from which syscalls will not produce a user dispatch.
+ */
+struct ptrace_sud_config {
+ __u8 mode;
+ __u8 pad[7];
+ __u64 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 22396b234854..08e8b377557f 100644
--- a/kernel/entry/syscall_user_dispatch.c
+++ b/kernel/entry/syscall_user_dispatch.c
@@ -4,6 +4,7 @@
*/
#include <linux/sched.h>
#include <linux/prctl.h>
+#include <linux/ptrace.h>
#include <linux/syscall_user_dispatch.h>
#include <linux/uaccess.h>
#include <linux/signal.h>
@@ -113,3 +114,42 @@ int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
{
return task_set_syscall_user_dispatch(current, mode, offset, len, selector);
}
+
+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 ptrace_sud_config config;
+ if (size != sizeof(struct ptrace_sud_config))
+ return -EINVAL;
+
+ if (test_task_syscall_work(task, 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 = (__u64)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)
+{
+ int rc;
+ struct ptrace_sud_config cfg;
+ if (size != sizeof(struct ptrace_sud_config))
+ return -EINVAL;
+
+ if (copy_from_user(&cfg, data, sizeof(cfg))) {
+ return -EFAULT;
+ }
+ rc = task_set_syscall_user_dispatch(task, cfg.mode, cfg.offset,
+ cfg.len, (void __user*)cfg.selector);
+ return rc;
+}
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 54482193e1ed..d99376532b56 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_* */

@@ -1259,6 +1260,14 @@ 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;
}
diff --git a/tools/testing/selftests/ptrace/.gitignore b/tools/testing/selftests/ptrace/.gitignore
index 792318aaa30c..b7dde152e75a 100644
--- a/tools/testing/selftests/ptrace/.gitignore
+++ b/tools/testing/selftests/ptrace/.gitignore
@@ -1,4 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
get_syscall_info
+get_set_sud
peeksiginfo
vmaccess
diff --git a/tools/testing/selftests/ptrace/Makefile b/tools/testing/selftests/ptrace/Makefile
index 2f1f532c39db..33a36b73bcb9 100644
--- a/tools/testing/selftests/ptrace/Makefile
+++ b/tools/testing/selftests/ptrace/Makefile
@@ -1,6 +1,6 @@
# SPDX-License-Identifier: GPL-2.0-only
CFLAGS += -std=c99 -pthread -iquote../../../../include/uapi -Wall

-TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess
+TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess get_set_sud

include ../lib.mk
diff --git a/tools/testing/selftests/ptrace/get_set_sud.c b/tools/testing/selftests/ptrace/get_set_sud.c
new file mode 100644
index 000000000000..c4e7b87cab03
--- /dev/null
+++ b/tools/testing/selftests/ptrace/get_set_sud.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include "../kselftest_harness.h"
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/wait.h>
+#include <sys/syscall.h>
+#include <sys/prctl.h>
+
+#include "linux/ptrace.h"
+
+static int sys_ptrace(int request, pid_t pid, void *addr, void *data)
+{
+ return syscall(SYS_ptrace, request, pid, addr, data);
+}
+
+TEST(get_set_sud)
+{
+ struct ptrace_sud_config config;
+ pid_t child;
+ int ret = 0;
+ int status;
+
+ child = fork();
+ ASSERT_GE(child, 0);
+ if (child == 0) {
+ ASSERT_EQ(0, sys_ptrace(PTRACE_TRACEME, 0, 0, 0)) {
+ TH_LOG("PTRACE_TRACEME: %m");
+ }
+ kill(getpid(), SIGSTOP);
+ _exit(1);
+ }
+
+ waitpid(child, &status, 0);
+
+ memset(&config, 0xff, sizeof(config));
+ config.mode = PR_SYS_DISPATCH_ON;
+
+ ret = sys_ptrace(PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG, child,
+ (void*)sizeof(config), &config);
+ if (ret < 0) {
+ ASSERT_EQ(errno, EIO);
+ goto leave;
+ }
+
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(config.mode, PR_SYS_DISPATCH_OFF);
+ ASSERT_EQ(config.selector, 0);
+ ASSERT_EQ(config.offset, 0);
+ ASSERT_EQ(config.len, 0);
+
+ config.mode = PR_SYS_DISPATCH_ON;
+ config.selector = 0;
+ config.offset = 0x400000;
+ config.len = 0x1000;
+
+ ret = sys_ptrace(PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG, child,
+ (void*)sizeof(config), &config);
+
+ ASSERT_EQ(ret, 0);
+
+ memset(&config, 1, sizeof(config));
+ ret = sys_ptrace(PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG, child,
+ (void*)sizeof(config), &config);
+
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(config.mode, PR_SYS_DISPATCH_ON);
+ ASSERT_EQ(config.selector, 0);
+ ASSERT_EQ(config.offset, 0x400000);
+ ASSERT_EQ(config.len, 0x1000);
+
+leave:
+ kill(child, SIGKILL);
+}
+
+TEST_HARNESS_MAIN
--
2.39.1
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