x86: add support for gdt table in C

Author: rizlik

arch.mk

@@ -1012,6 +1012,7 @@ ifeq ("${FSP}", "1")
     OBJS += src/x86/mptable.o
     OBJS += src/stage2_params.o
     OBJS += src/x86/exceptions.o
+    OBJS += src/x86/gdt.o
     UPDATE_OBJS := src/update_disk.o
     CFLAGS+=-DWOLFBOOT_UPDATE_DISK
     ifeq ($(64BIT),1)

hal/kontron_vx3060_s2.c

@@ -24,6 +24,7 @@
 #include <uart_drv.h>
 #include <printf.h>
 #include <pci.h>
+#include <x86/gdt.h>
 #include <x86/common.h>
 
 #ifdef __WOLFBOOT
@@ -85,6 +86,8 @@ int tgl_lock_bios_region()
 
 void hal_init(void)
 {
+    gdt_setup_table();
+    gdt_update_segments();
 }
 
 void hal_prepare_boot(void)

hal/x86_fsp_qemu.c

@@ -26,14 +26,15 @@
 
 #ifdef __WOLFBOOT
 #include <printf.h>
-#include <x86/common.h>
-#include <x86/ahci.h>
 #include <x86/ata.h>
-#include <x86/gpt.h>
+#include <x86/gdt.h>
+#include <x86/common.h>
 #include <pci.h>
 
 void hal_init(void)
 {
+    gdt_setup_table();
+    gdt_update_segments();
 }
 
 void hal_prepare_boot(void)

include/x86/gdt.h

@@ -0,0 +1,32 @@
+/* gdt.h
+ *
+ * Copyright (C) 2023 wolfSSL Inc.
+ *
+ * This file is part of wolfBoot.
+ *
+ * wolfBoot is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * wolfBoot is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
+ */
+#ifndef GDT_H
+#define GDT_H
+
+#define GDT_DS (0x08)
+#define GDT_CS_32BIT (0x10)
+#define GDT_CS_64BIT (0x18)
+#define GDT_CS_32BIT_COMPAT (0x20)
+
+int gdt_setup_table(void);
+int gdt_update_segments(void);
+
+#endif /* GDT_H */

src/x86/gdt.c

@@ -0,0 +1,96 @@
+/* gdt.c
+ *
+ * Copyright (C) 2023 wolfSSL Inc.
+ *
+ * This file is part of wolfBoot.
+ *
+ * wolfBoot is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * wolfBoot is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
+ *
+ */
+#include <stdint.h>
+#include <x86/gdt.h>
+
+struct segment_descriptor {
+    uint16_t seg_limit_15_0;
+    uint16_t base_addr_15_0;
+    uint8_t base_addr_23_16;
+    uint8_t type_s_dpl_p;
+    uint8_t seg_limt_19_16_avl_flags;
+    uint8_t base_addr_31_24;
+} __attribute__((packed));
+
+struct gdtr_32 {
+    uint16_t limit;
+    uint32_t base;
+} __attribute__((packed));
+
+struct gdtr_64 {
+    uint16_t limit;
+    uint64_t base;
+} __attribute__((packed));
+
+#define SEGMENT_DESCRIPTOR_INIT(base, limit, type, s, dpl, p, avl, l, db, g) { \
+    .seg_limit_15_0 = (limit) & 0xffff, \
+    .base_addr_15_0 = (base) & 0xffff, \
+    .base_addr_23_16 = (((base) >> 16) & 0xff), \
+    .type_s_dpl_p = ((type & 0xf) | ((s & 0x1) << 4) | ((dpl & 0x3) << 5) |  ((p & 0x1) << 7)), \
+    .seg_limt_19_16_avl_flags = ((((limit) >> 16) & 0xf) | ((avl & 0x1) << 4) | ((l & 0x1) << 5) | ((db & 0x1) << 6) | ((g & 0x1) << 7)), \
+    .base_addr_31_24 = ((base) >> 24) & 0xff, \
+}
+
+#define GDT_NUM_ENTRIES 5
+
+struct segment_descriptor gdt[GDT_NUM_ENTRIES] =  {
+    /* NULL */
+    SEGMENT_DESCRIPTOR_INIT(0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
+    /* Data */
+    SEGMENT_DESCRIPTOR_INIT(0, 0xffffffff, 0x3, 1, 0, 1, 0, 0, 1, 1),
+    /* Code (32bit) */
+    SEGMENT_DESCRIPTOR_INIT(0, 0xffffffff, 0xb, 1, 0, 1, 0, 0, 1, 1),
+    /* Code (64bit) */
+    SEGMENT_DESCRIPTOR_INIT(0, 0xffffffff, 0xb, 1, 0, 1, 0, 1, 0, 1),
+    /* Code (64bit) compat mode */
+    SEGMENT_DESCRIPTOR_INIT(0, 0xffffffff, 0xb, 1, 0, 1, 0, 0, 1, 1),
+};
+
+int gdt_setup_table(void)
+{
+    struct gdtr_64 gdtr;
+    gdtr.limit = sizeof(gdt) - 1;
+    gdtr.base = (uint64_t)(uintptr_t)gdt;
+    __asm__ volatile ("lgdt %0" : : "m" (gdtr));
+    return 0;
+}
+
+int gdt_update_segments(void)
+{
+    __asm__ volatile (
+        "mov %0, %%ax\r\n"
+        "mov %%ax, %%ds\r\n"
+        "mov %%ax, %%es\r\n"
+        "mov %%ax, %%fs\r\n"
+        "mov %%ax, %%gs\r\n"
+        "mov %%ax, %%ss\r\n"
+        "push %1\r\n"
+        "lea (seg_cs), %%rax\r\n"
+        "push %%rax\r\n"
+        "retfq\r\n"
+        "seg_cs:\r\n"
+        :
+        : "i"(GDT_DS), "i" (GDT_CS_64BIT) 
+        : "rax"
+    );
+    return 0;
+}