Kernel: Add support for setting up a x86_64 GDT once in C++ land

5 files changed, 55 insertions, 11 deletions

diff --git a/Kernel/Arch/x86/ASM_wrapper.h b/Kernel/Arch/x86/ASM_wrapper.h
index 9962247402..cd5782a692 100644
--- a/Kernel/Arch/x86/ASM_wrapper.h
+++ b/Kernel/Arch/x86/ASM_wrapper.h
@@ -30,6 +30,7 @@ ALWAYS_INLINE FlatPtr cpu_flags()
     return flags;
 }
 
+#if ARCH(I386)
 ALWAYS_INLINE void set_fs(u16 segment)
 {
     asm volatile(
@@ -59,6 +60,7 @@ ALWAYS_INLINE u16 get_gs()
         : "=a"(gs));
     return gs;
 }
+#endif
 
 ALWAYS_INLINE u32 read_fs_u32(u32 offset)
 {
diff --git a/Kernel/Arch/x86/DescriptorTable.h b/Kernel/Arch/x86/DescriptorTable.h
index 6fe76fd411..2cfdff8301 100644
--- a/Kernel/Arch/x86/DescriptorTable.h
+++ b/Kernel/Arch/x86/DescriptorTable.h
@@ -10,13 +10,14 @@
 #include <AK/Types.h>
 #include <Kernel/VirtualAddress.h>
 
-#define GDT_SELECTOR_CODE0 0x08
-#define GDT_SELECTOR_DATA0 0x10
-#define GDT_SELECTOR_CODE3 0x18
-#define GDT_SELECTOR_DATA3 0x20
-#define GDT_SELECTOR_TLS 0x28
-#define GDT_SELECTOR_PROC 0x30
-#define GDT_SELECTOR_TSS 0x38
+#if ARCH(I386)
+#    define GDT_SELECTOR_CODE0 0x08
+#    define GDT_SELECTOR_DATA0 0x10
+#    define GDT_SELECTOR_CODE3 0x18
+#    define GDT_SELECTOR_DATA3 0x20
+#    define GDT_SELECTOR_TLS 0x28
+#    define GDT_SELECTOR_PROC 0x30
+#    define GDT_SELECTOR_TSS 0x38
 
 // SYSENTER makes certain assumptions on how the GDT is structured:
 static_assert(GDT_SELECTOR_CODE0 + 8 == GDT_SELECTOR_DATA0); // SS0 = CS0 + 8
@@ -24,6 +25,12 @@ static_assert(GDT_SELECTOR_CODE0 + 8 == GDT_SELECTOR_DATA0); // SS0 = CS0 + 8
 // SYSEXIT makes certain assumptions on how the GDT is structured:
 static_assert(GDT_SELECTOR_CODE0 + 16 == GDT_SELECTOR_CODE3); // CS3 = CS0 + 16
 static_assert(GDT_SELECTOR_CODE0 + 24 == GDT_SELECTOR_DATA3); // SS3 = CS0 + 32
+#else
+#    define GDT_SELECTOR_CODE0 0x08
+#    define GDT_SELECTOR_CODE3 0x10
+#    define GDT_SELECTOR_TSS 0x18
+#    define GDT_SELECTOR_TSS_PART2 0x20
+#endif
 
 namespace Kernel {
 
@@ -82,6 +89,7 @@ union [[gnu::packed]] Descriptor {
         base_lo = base.get() & 0xffffu;
         base_hi = (base.get() >> 16u) & 0xffu;
         base_hi2 = (base.get() >> 24u) & 0xffu;
+        VERIFY(base.get() <= 0xffffffff);
     }
 
     void set_limit(u32 length)
@@ -91,6 +99,8 @@ union [[gnu::packed]] Descriptor {
     }
 };
 
+static_assert(sizeof(Descriptor) == 8);
+
 enum class IDTEntryType {
     TaskGate32 = 0b0101,
     InterruptGate16 = 0b110,
diff --git a/Kernel/Arch/x86/Processor.h b/Kernel/Arch/x86/Processor.h
index 5565d9c81f..cdd551ede3 100644
--- a/Kernel/Arch/x86/Processor.h
+++ b/Kernel/Arch/x86/Processor.h
@@ -19,6 +19,11 @@
 
 namespace Kernel {
 
+#if ARCH(X86_64)
+#    define MSR_FS_BASE 0xc0000100
+#    define MSR_GS_BASE 0xc0000102
+#endif
+
 class Thread;
 class SchedulerPerProcessorData;
 struct MemoryManagerData;
@@ -241,7 +246,11 @@ public:
 
     ALWAYS_INLINE static bool is_initialized()
     {
-        return get_fs() == GDT_SELECTOR_PROC && read_fs_u32(__builtin_offsetof(Processor, m_self)) != 0;
+        return
+#if ARCH(I386)
+            get_fs() == GDT_SELECTOR_PROC &&
+#endif
+            read_fs_u32(__builtin_offsetof(Processor, m_self)) != 0;
     }
 
     ALWAYS_INLINE void set_scheduler_data(SchedulerPerProcessorData& scheduler_data)
diff --git a/Kernel/Arch/x86/common/Processor.cpp b/Kernel/Arch/x86/common/Processor.cpp
index cb84c12ac7..5647b4ec2d 100644
--- a/Kernel/Arch/x86/common/Processor.cpp
+++ b/Kernel/Arch/x86/common/Processor.cpp
@@ -19,6 +19,7 @@
 
 #include <Kernel/Arch/x86/CPUID.h>
 #include <Kernel/Arch/x86/Interrupts.h>
+#include <Kernel/Arch/x86/MSR.h>
 #include <Kernel/Arch/x86/Processor.h>
 #include <Kernel/Arch/x86/ProcessorInfo.h>
 #include <Kernel/Arch/x86/SafeMem.h>
@@ -1056,11 +1057,17 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
     m_gdtr.limit = 0;
 
     write_raw_gdt_entry(0x0000, 0x00000000, 0x00000000);
+#if ARCH(I386)
     write_raw_gdt_entry(GDT_SELECTOR_CODE0, 0x0000ffff, 0x00cf9a00); // code0
     write_raw_gdt_entry(GDT_SELECTOR_DATA0, 0x0000ffff, 0x00cf9200); // data0
     write_raw_gdt_entry(GDT_SELECTOR_CODE3, 0x0000ffff, 0x00cffa00); // code3
     write_raw_gdt_entry(GDT_SELECTOR_DATA3, 0x0000ffff, 0x00cff200); // data3
+#else
+    write_raw_gdt_entry(GDT_SELECTOR_CODE0, 0x0000ffff, 0x00ef9a00); // code0
+    write_raw_gdt_entry(GDT_SELECTOR_CODE3, 0x0000ffff, 0x00effa00); // code3
+#endif
 
+#if ARCH(I386)
     Descriptor tls_descriptor {};
     tls_descriptor.low = tls_descriptor.high = 0;
     tls_descriptor.dpl = 3;
@@ -1083,10 +1090,11 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
     fs_descriptor.descriptor_type = 1;
     fs_descriptor.type = 2;
     write_gdt_entry(GDT_SELECTOR_PROC, fs_descriptor); // fs0
+#endif
 
     Descriptor tss_descriptor {};
-    tss_descriptor.set_base(VirtualAddress { &m_tss });
-    tss_descriptor.set_limit(sizeof(TSS32) - 1);
+    tss_descriptor.set_base(VirtualAddress { (size_t)&m_tss & 0xffffffff });
+    tss_descriptor.set_limit(sizeof(TSS) - 1);
     tss_descriptor.dpl = 0;
     tss_descriptor.segment_present = 1;
     tss_descriptor.granularity = 0;
@@ -1096,9 +1104,21 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
     tss_descriptor.type = 9;
     write_gdt_entry(GDT_SELECTOR_TSS, tss_descriptor); // tss
 
+#if ARCH(X86_64)
+    Descriptor tss_descriptor_part2 {};
+    tss_descriptor_part2.low = (size_t)&m_tss >> 32;
+    write_gdt_entry(GDT_SELECTOR_TSS_PART2, tss_descriptor_part2);
+#endif
+
     flush_gdt();
     load_task_register(GDT_SELECTOR_TSS);
 
+#if ARCH(X86_64)
+    MSR fs_base(MSR_FS_BASE);
+    fs_base.set((size_t)this & 0xffffffff, (size_t)this >> 32);
+#endif
+
+#if ARCH(I386)
     asm volatile(
         "mov %%ax, %%ds\n"
         "mov %%ax, %%es\n"
@@ -1107,7 +1127,6 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
         : "memory");
     set_fs(GDT_SELECTOR_PROC);
 
-#if ARCH(I386)
     // Make sure CS points to the kernel code descriptor.
     // clang-format off
     asm volatile(
diff --git a/Kernel/Syscalls/mmap.cpp b/Kernel/Syscalls/mmap.cpp
index d5a5dd6457..1412d0656e 100644
--- a/Kernel/Syscalls/mmap.cpp
+++ b/Kernel/Syscalls/mmap.cpp
@@ -607,9 +607,13 @@ KResultOr<FlatPtr> Process::sys$allocate_tls(Userspace<const char*> initial_data
     if (tsr_result.is_error())
         return EFAULT;
 
+#if ARCH(I386)
     auto& tls_descriptor = Processor::current().get_gdt_entry(GDT_SELECTOR_TLS);
     tls_descriptor.set_base(main_thread->thread_specific_data());
     tls_descriptor.set_limit(main_thread->thread_specific_region_size());
+#else
+    TODO();
+#endif
 
     return m_master_tls_region.unsafe_ptr()->vaddr().get();
 }