usermode: add sysenter and syscall_mode selection

To give usermode the option to choose sysenter instead of syscall, we expose syscall_mode(enum syscall_mode), which is by default using syscall. Signed-off-by: Johannes Wikner <[email protected]>
KernelTestFramework · Aug 30, 2023 · eec2373 · eec2373
1 parent 683d273
commit eec2373
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Showing 3 changed files with 59 additions and 8 deletions.
diff --git a/arch/x86/entry.S b/arch/x86/entry.S
@@ -224,9 +224,7 @@ ENTRY(syscall_handler_entry)
 END_FUNC(syscall_handler_entry)
 
 ENTRY(sysenter_handler_entry)
-    push %_ASM_CX
-    push %_ASM_DX
-    SAVE_CALLEE_SAVED_REGS
+    SAVE_ALL_REGS
     syscall_from_usermode
 
     MASK_USER_FLAGS
@@ -240,9 +238,7 @@ ENTRY(sysenter_handler_entry)
     call syscall_handler
 
     syscall_to_usermode
-    RESTORE_CALLEE_SAVED_REGS
-    pop %_ASM_DX
-    pop %_ASM_CX
+    RESTORE_ALL_REGS
 
     SYSEXIT
 END_FUNC(sysenter_handler_entry)

diff --git a/common/usermode.c b/common/usermode.c
@@ -113,8 +113,8 @@ void init_usermode(percpu_t *percpu) {
     init_sysenter(percpu);
 }
 
-static inline long __user_text syscall(long syscall_nr, long arg1, long arg2, long arg3,
-                                       long arg4, long arg5) {
+static inline long __user_text _syscall(long syscall_nr, long arg1, long arg2, long arg3,
+                                        long arg4, long arg5) {
     register long return_code asm(STR(_ASM_AX));
     register long _arg4 asm("r8") = arg4;
     register long _arg5 asm("r9") = arg5;
@@ -131,6 +131,53 @@ static inline long __user_text syscall(long syscall_nr, long arg1, long arg2, lo
     return return_code;
 }
 
+static inline long __user_text _sysenter(long syscall_nr, long arg1, long arg2, long arg3,
+                                         long arg4, long arg5) {
+    register long return_code asm(STR(_ASM_AX));
+    register long _arg4 asm("r8") = arg4;
+    register long _arg5 asm("r9") = arg5;
+    register long _arg3 asm("r10") = arg3;
+
+    /* clang-format off */
+    asm volatile (
+        "mov %%" STR(_ASM_SP) ", %%" STR(_ASM_CX) "\n"
+        "lea 1f(%%" STR(_ASM_IP) "), %%" STR(_ASM_DX) "\n"
+        "sysenter\n"
+        "1: "
+        : "=a"(return_code)
+        : "0"(syscall_nr), "S"(arg1), "D" (arg2), "r" (_arg3), "r"(_arg4), "r"(_arg5)
+        : STR(_ASM_CX), STR(_ASM_DX)
+    );
+    /* clang-format on */
+
+    return return_code;
+}
+
+static __user_data syscall_mode_t sc_mode = SYSCALL_MODE_SYSCALL;
+
+bool __user_text syscall_mode(syscall_mode_t mode) {
+    if (mode > SYSCALL_MODE_INT) {
+        return false;
+    }
+    sc_mode = mode;
+
+    return true;
+}
+
+static long __user_text syscall(long syscall_nr, long arg1, long arg2, long arg3,
+                                long arg4, long arg5) {
+    switch (sc_mode) {
+    case SYSCALL_MODE_SYSCALL:
+        return _syscall(syscall_nr, arg1, arg2, arg3, arg4, arg5);
+    case SYSCALL_MODE_SYSENTER:
+        return _sysenter(syscall_nr, arg1, arg2, arg3, arg4, arg5);
+    case SYSCALL_MODE_INT:
+        // unimplemented
+    default:
+        UNREACHABLE();
+    }
+}
+
 #define syscall0(nr)                     syscall((nr), 0, 0, 0, 0, 0)
 #define syscall1(nr, a1)                 syscall((nr), (a1), 0, 0, 0, 0)
 #define syscall2(nr, a1, a2)             syscall((nr), (a1), (a2), 0, 0, 0)

diff --git a/include/usermode.h b/include/usermode.h
@@ -39,6 +39,13 @@
 #include <percpu.h>
 #include <sched.h>
 
+enum syscall_mode {
+    SYSCALL_MODE_SYSCALL,  // use SYSCALL
+    SYSCALL_MODE_SYSENTER, // use SYSENTER
+    SYSCALL_MODE_INT,      // TODO: use INT $SYSVEC
+};
+typedef enum syscall_mode syscall_mode_t;
+
 /* Static declarations */
 
 static inline bool enter_from_usermode(uint16_t cs) {
@@ -57,6 +64,7 @@ extern void __user_text exit(unsigned long exit_code);
 extern void __user_text printf(const char *fmt, ...);
 extern void *__user_text mmap(void *va, unsigned long order);
 extern void __user_text munmap(void *va, unsigned long order);
+extern bool __user_text syscall_mode(syscall_mode_t);
 
 #endif /* __ASSEMBLY__ */