usermode: support int 80h syscalls

From usermode's perspective it works the same as syscall. Signed-off-by: Johannes Wikner <[email protected]> Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
KernelTestFramework · Aug 30, 2023 · e9b57fd · e9b57fd
1 parent eec2373
commit e9b57fd
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Showing 4 changed files with 45 additions and 4 deletions.
diff --git a/arch/x86/entry.S b/arch/x86/entry.S
@@ -242,6 +242,24 @@ ENTRY(sysenter_handler_entry)
 
     SYSEXIT
 END_FUNC(sysenter_handler_entry)
+
+ENTRY(int80_handler_entry)
+    SAVE_ALL_REGS
+    syscall_from_usermode
+
+    MASK_USER_FLAGS
+
+    cmp $SYSCALL_EXIT, %_ASM_AX
+    jz syscall_exit
+
+    mov %_ASM_DI, %_ASM_CX
+    mov %_ASM_AX, %_ASM_DI
+    call syscall_handler
+
+    syscall_to_usermode
+    RESTORE_ALL_REGS
+    IRET
+END_FUNC(int80_handler_entry)
 GLOBAL(end_usermode_helpers)
 
 SECTION(.text.user, "ax", 16)

diff --git a/common/usermode.c b/common/usermode.c
@@ -27,6 +27,7 @@
 #include <pagetable.h>
 #include <percpu.h>
 #include <processor.h>
+#include <traps.h>
 #include <usermode.h>
 
 extern char exception_handlers[], end_exception_handlers[];
@@ -111,6 +112,25 @@ void init_usermode(percpu_t *percpu) {
 
     init_syscall();
     init_sysenter(percpu);
+    set_intr_gate(&percpu->idt[SYSCALL_INT], __KERN_CS, _ul(int80_handler_entry),
+                  GATE_DPL3, GATE_PRESENT, 0);
+}
+
+static inline long __user_text _int80(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;
+
+    /* clang-format off */
+    asm volatile(
+        "int $" STR(SYSCALL_INT) "\n"
+        : "=a"(return_code)
+        : "0"(syscall_nr), "S"(arg1), "d"(arg2), "D" (arg3), "r"(_arg4), "r"(_arg5)
+    );
+    /* clang-format on */
+
+    return return_code;
 }
 
 static inline long __user_text _syscall(long syscall_nr, long arg1, long arg2, long arg3,
@@ -156,7 +176,7 @@ static inline long __user_text _sysenter(long syscall_nr, long arg1, long arg2,
 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) {
+    if (mode > SYSCALL_MODE_INT80) {
         return false;
     }
     sc_mode = mode;
@@ -171,8 +191,8 @@ static long __user_text syscall(long syscall_nr, long arg1, long arg2, long arg3
         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
+    case SYSCALL_MODE_INT80:
+        return _int80(syscall_nr, arg1, arg2, arg3, arg4, arg5);
     default:
         UNREACHABLE();
     }

diff --git a/include/arch/x86/traps.h b/include/arch/x86/traps.h
@@ -30,6 +30,8 @@
 
 #define MAX_INT 256
 
+#define SYSCALL_INT 0x80
+
 #ifndef __ASSEMBLY__
 #include <cpu.h>
 

diff --git a/include/usermode.h b/include/usermode.h
@@ -42,7 +42,7 @@
 enum syscall_mode {
     SYSCALL_MODE_SYSCALL,  // use SYSCALL
     SYSCALL_MODE_SYSENTER, // use SYSENTER
-    SYSCALL_MODE_INT,      // TODO: use INT $SYSVEC
+    SYSCALL_MODE_INT80,    // use INT 0x80
 };
 typedef enum syscall_mode syscall_mode_t;
 
@@ -57,6 +57,7 @@ static inline bool enter_from_usermode(uint16_t cs) {
 extern unsigned long enter_usermode(task_func_t fn, void *fn_arg, void *user_stack);
 extern void syscall_handler_entry(void);
 extern void sysenter_handler_entry(void);
+extern void int80_handler_entry(void);
 
 extern void init_usermode(percpu_t *percpu);