Add rings 1 & 2 to GDT entries

XyrisOS · Jun 17, 2021 · 1f3a5b7 · 1f3a5b7
1 parent fa70a3c
commit 1f3a5b7
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Showing 3 changed files with 29 additions and 5 deletions.
diff --git a/kernel/arch/i386/flush.s b/kernel/arch/i386/flush.s
@@ -33,7 +33,7 @@ gdt_flush:
 # Allows our code to call tss_flush().
 .global tss_flush
 tss_flush:
-    mov $0x2B, %ax  # Load the index of our TSS structure - The index is
+    mov $0x4B, %ax  # Load the index of our TSS structure - The index is
                     # 0x28, as it is the 5th selector and each is 8 bytes
                     # long, but we set the bottom two bits (making 0x2B)
                     # so that it has an RPL of 3, not zero.

diff --git a/kernel/arch/i386/gdt.cpp b/kernel/arch/i386/gdt.cpp
@@ -15,7 +15,7 @@
 #include <lib/stdio.hpp>
 #include <dev/tty/tty.hpp>
 
-#define GDT_NUM_ENTRIES 6
+#define GDT_NUM_ENTRIES 10
 
 // Defined in the gdt_flush.s file.
 extern "C" void gdt_flush(uintptr_t);
@@ -84,9 +84,13 @@ void gdt_install() {
     gdt_set_gate(0, 0, 0, 0);                     // Null segment
     gdt_set_gate(1, 0, 0x000FFFFF, GDT_CODE_PL0); // Kernel code segment
     gdt_set_gate(2, 0, 0x000FFFFF, GDT_DATA_PL0); // Kernel data segment
-    gdt_set_gate(3, 0, 0x000FFFFF, GDT_CODE_PL3); // User mode code segment
-    gdt_set_gate(4, 0, 0x000FFFFF, GDT_DATA_PL3); // User mode data segment
-    tss_set_gate(5, 0x10, 0x0);                   // TSS entry
+    gdt_set_gate(3, 0, 0x000FFFFF, GDT_CODE_PL1); // Reserved code segment
+    gdt_set_gate(4, 0, 0x000FFFFF, GDT_DATA_PL1); // Reserved data segment
+    gdt_set_gate(5, 0, 0x000FFFFF, GDT_CODE_PL2); // Driver code segment
+    gdt_set_gate(6, 0, 0x000FFFFF, GDT_DATA_PL2); // Driver data segment
+    gdt_set_gate(7, 0, 0x000FFFFF, GDT_CODE_PL3); // User mode code segment
+    gdt_set_gate(8, 0, 0x000FFFFF, GDT_DATA_PL3); // User mode data segment
+    tss_set_gate(9, 0x10, 0x0);                   // TSS entry
 
     gdt_flush((uint32_t)&gdt_ptr);
     tss_flush();

diff --git a/sysroot/usr/include/kernel/arch/i386/gdt.hpp b/sysroot/usr/include/kernel/arch/i386/gdt.hpp
@@ -44,6 +44,7 @@
 #define SEG_CODE_EXRDC       0x0E   // Execute/Read, conforming
 #define SEG_CODE_EXRDCA      0x0F   // Execute/Read, conforming, accessed
 
+// Ring 0 Privilege Levels (Kernel)
 #define GDT_CODE_PL0 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
                      SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
                      SEG_PRIV(0) | SEG_CODE_EXRD
@@ -52,6 +53,25 @@
                      SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
                      SEG_PRIV(0) | SEG_DATA_RDWR
 
+// Ring 1 Privilege Levels (Reserved)
+#define GDT_CODE_PL1 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(1) | SEG_CODE_EXRD
+
+#define GDT_DATA_PL1 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(1) | SEG_DATA_RDWR
+
+// Ring 2 Privilege Levels (Reserved for drivers)
+#define GDT_CODE_PL2 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(2) | SEG_CODE_EXRD
+
+#define GDT_DATA_PL2 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
+                     SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
+                     SEG_PRIV(2) | SEG_DATA_RDWR
+
+// Ring 3 Privilege Levels (Userspace)
 #define GDT_CODE_PL3 SEG_TYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
                      SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
                      SEG_PRIV(3) | SEG_CODE_EXRD