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Kernel: Fix GDT and segment selectors to make userland work on x86_64

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Userland faulted on the very first instruction before because the
PML4T/PDPT/etc. weren't marked as user-accessible. For some reason
x86 doesn't care about that.

Also, we need to provide an appropriate userspace stack segment
selector to iretq.
This commit is contained in:
Gunnar Beutner 2021-06-28 17:03:08 +02:00 committed by Andreas Kling
parent 04fc7d708c
commit b5aad1c81d
Notes: sideshowbarker 2024-07-18 11:23:01 +09:00 
Author: https://github.com/gunnarbeutner
Commit: https://github.com/SerenityOS/serenity/commit/b5aad1c81d1
Pull-request: https://github.com/SerenityOS/serenity/pull/8301
4 changed files with 16 additions and 9 deletions
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5
Kernel/Arch/x86/DescriptorTable.h
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@ -28,8 +28,9 @@ static_assert(GDT_SELECTOR_CODE0 + 24 == GDT_SELECTOR_DATA3); // SS3 = CS0 + 32
#else #else
# define GDT_SELECTOR_CODE0 0x08 # define GDT_SELECTOR_CODE0 0x08
# define GDT_SELECTOR_CODE3 0x10 # define GDT_SELECTOR_CODE3 0x10
# define GDT_SELECTOR_TSS 0x18 # define GDT_SELECTOR_DATA3 0x18
# define GDT_SELECTOR_TSS_PART2 0x20 # define GDT_SELECTOR_TSS 0x20
# define GDT_SELECTOR_TSS_PART2 0x28
#endif #endif
namespace Kernel { namespace Kernel {

1
Kernel/Arch/x86/common/Processor.cpp
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@ -1070,6 +1070,7 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
#else #else
write_raw_gdt_entry(GDT_SELECTOR_CODE0, 0x0000ffff, 0x00af9a00); // code0 write_raw_gdt_entry(GDT_SELECTOR_CODE0, 0x0000ffff, 0x00af9a00); // code0
write_raw_gdt_entry(GDT_SELECTOR_CODE3, 0x0000ffff, 0x00affa00); // code3 write_raw_gdt_entry(GDT_SELECTOR_CODE3, 0x0000ffff, 0x00affa00); // code3
write_raw_gdt_entry(GDT_SELECTOR_DATA3, 0x0000ffff, 0x008ff200); // data3
#endif #endif
#if ARCH(I386) #if ARCH(I386)

5
Kernel/Arch/x86/x86_64/Processor.cpp
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@ -115,8 +115,13 @@ u32 Processor::init_context(Thread& thread, bool leave_crit)
iretframe.rflags = regs.rflags; iretframe.rflags = regs.rflags;
iretframe.rip = regs.rip; iretframe.rip = regs.rip;
iretframe.cs = regs.cs; iretframe.cs = regs.cs;
if (return_to_user) {
iretframe.userspace_rsp = regs.rsp;
iretframe.userspace_ss = GDT_SELECTOR_DATA3 | 3;
} else {
iretframe.userspace_rsp = kernel_stack_top; iretframe.userspace_rsp = kernel_stack_top;
iretframe.userspace_ss = 0; iretframe.userspace_ss = 0;
}
// make space for a trap frame // make space for a trap frame
stack_top -= sizeof(TrapFrame); stack_top -= sizeof(TrapFrame);

10
Kernel/VM/PageDirectory.cpp
View File

@ -95,7 +95,7 @@ PageDirectory::PageDirectory(const RangeAllocator* parent_range_allocator)
#if ARCH(X86_64) #if ARCH(X86_64)
{ {
auto& table = *(PageDirectoryPointerTable*)MM.quickmap_page(*m_pml4t); auto& table = *(PageDirectoryPointerTable*)MM.quickmap_page(*m_pml4t);
table.raw[0] = (FlatPtr)m_directory_table->paddr().as_ptr() | 3; table.raw[0] = (FlatPtr)m_directory_table->paddr().as_ptr() | 7;
MM.unquickmap_page(); MM.unquickmap_page();
} }
#endif #endif
@ -108,10 +108,10 @@ PageDirectory::PageDirectory(const RangeAllocator* parent_range_allocator)
table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 1; table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 1;
table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 1; table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 1;
#else #else
table.raw[0] = (FlatPtr)m_directory_pages[0]->paddr().as_ptr() | 3; table.raw[0] = (FlatPtr)m_directory_pages[0]->paddr().as_ptr() | 7;
table.raw[1] = (FlatPtr)m_directory_pages[1]->paddr().as_ptr() | 3; table.raw[1] = (FlatPtr)m_directory_pages[1]->paddr().as_ptr() | 7;
table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 3; table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 7;
table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 3; table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 7;
#endif #endif
// 2 ** MAXPHYADDR - 1 // 2 ** MAXPHYADDR - 1