kernel: handle ksud execve by syscall_hook_manager, use static_key

This should solves conflicts with other kernel module (for example, kpatch-next).
TODO: move other ksud syscall hook to syscall_hook_manager

Author: 5ec1cff

kernel/ksud.c

@@ -229,7 +229,7 @@ void ksu_handle_execveat_ksud(const char *path, struct user_arg_ptr *argv)
             pr_info("exec zygote, /data prepared, second_stage: %d\n", init_second_stage_executed);
             on_post_fs_data();
             first_zygote = false;
-            stop_execve_hook();
+            ksu_stop_ksud_execve_hook();
         }
     }
 }
@@ -435,8 +435,7 @@ bool ksu_is_safe_mode()
     return false;
 }
 
-static long (*orig_sys_execve)(const struct pt_regs *regs);
-static long ksu_sys_execve(const struct pt_regs *regs)
+void ksu_execve_hook_ksud(const struct pt_regs *regs)
 {
     const char __user **filename_user = (const char **)&PT_REGS_PARM1(regs);
     const char __user *const __user *__argv = (const char __user *const __user *)PT_REGS_PARM2(regs);
@@ -447,7 +446,7 @@ static long ksu_sys_execve(const struct pt_regs *regs)
     const char __user *fn;
 
     if (!filename_user)
-        goto do_orig;
+        return;
 
     addr = untagged_addr((unsigned long)*filename_user);
     fn = (const char __user *)addr;
@@ -456,13 +455,10 @@ static long ksu_sys_execve(const struct pt_regs *regs)
     ret = strncpy_from_user(path, fn, 32);
     if (ret < 0) {
         pr_err("Access filename failed for execve_handler_pre\n");
-        goto do_orig;
+        return;
     }
 
     ksu_handle_execveat_ksud(path, &argv);
-
-do_orig:
-    return orig_sys_execve(regs);
 }
 
 static long (*orig_sys_read)(const struct pt_regs *regs);
@@ -539,12 +535,6 @@ static void stop_init_rc_hook()
     pr_info("unregister init_rc syscall hook\n");
 }
 
-static void stop_execve_hook()
-{
-    ksu_syscall_table_unhook(__NR_execve);
-    pr_info("unhook sys_execve\n");
-}
-
 static void stop_input_hook()
 {
     static bool input_hook_stopped = false;
@@ -561,7 +551,6 @@ void ksu_ksud_init()
 {
     int ret;
 
-    ksu_syscall_table_hook(__NR_execve, ksu_sys_execve, &orig_sys_execve);
     ksu_syscall_table_hook(__NR_read, ksu_sys_read, &orig_sys_read);
     ksu_syscall_table_hook(__NR_fstat, ksu_sys_fstat, &orig_sys_fstat);
 
@@ -573,7 +562,6 @@ void ksu_ksud_init()
 
 void ksu_ksud_exit()
 {
-    stop_execve_hook();
     // TODO:
     // this should be done before unregister vfs_read_kp
     // stop_init_rc_hook();

kernel/ksud.h

@@ -2,6 +2,7 @@
 #define __KSU_H_KSUD
 
 #include <linux/types.h>
+#include <asm/syscall.h>
 
 #define KSUD_PATH "/data/adb/ksud"
 
@@ -20,4 +21,7 @@ extern u32 ksu_file_sid;
 extern bool ksu_module_mounted;
 extern bool ksu_boot_completed;
 
+void ksu_execve_hook_ksud(const struct pt_regs *regs);
+void ksu_stop_ksud_execve_hook();
+
 #endif

kernel/syscall_hook_manager.c

@@ -1,5 +1,6 @@
 #include "linux/compiler.h"
 #include "linux/cred.h"
+#include "linux/jump_label.h"
 #include "linux/printk.h"
 #include "selinux/selinux.h"
 #include <linux/spinlock.h>
@@ -9,6 +10,7 @@
 #include <linux/ptrace.h>
 #include <linux/slab.h>
 #include <trace/events/syscalls.h>
+#include <linux/static_key.h>
 
 #include "arch.h"
 #include "klog.h" // IWYU pragma: keep
@@ -150,12 +152,21 @@ static long __nocfi ksu_hook_faccessat(int orig_nr, const struct pt_regs *regs)
     return ksu_syscall_table[orig_nr](regs);
 }
 
+DEFINE_STATIC_KEY_TRUE(ksud_execve_key);
+
+void ksu_stop_ksud_execve_hook()
+{
+    static_branch_disable(&ksud_execve_key);
+}
+
 static long __nocfi ksu_hook_execve(int orig_nr, const struct pt_regs *regs)
 {
     int ret = 0;
 
     const char __user **filename_user = (const char __user **)&PT_REGS_PARM1(regs);
     bool current_is_init = is_init(current_cred());
+    if (static_branch_unlikely(&ksud_execve_key))
+        ksu_execve_hook_ksud(regs);
     if (current->pid != 1 && current_is_init) {
         ksu_handle_init_mark_tracker(filename_user);
     } else if (ksu_su_compat_enabled) {