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Kernel: Fix GDT and segment selectors to make userland work on x86_64
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.
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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
@ -28,8 +28,9 @@ static_assert(GDT_SELECTOR_CODE0 + 24 == GDT_SELECTOR_DATA3); // SS3 = CS0 + 32
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#else
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# define GDT_SELECTOR_CODE0 0x08
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# define GDT_SELECTOR_CODE3 0x10
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# define GDT_SELECTOR_TSS 0x18
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# define GDT_SELECTOR_TSS_PART2 0x20
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# define GDT_SELECTOR_DATA3 0x18
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# define GDT_SELECTOR_TSS 0x20
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# define GDT_SELECTOR_TSS_PART2 0x28
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#endif
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namespace Kernel {
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@ -1070,6 +1070,7 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
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#else
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write_raw_gdt_entry(GDT_SELECTOR_CODE0, 0x0000ffff, 0x00af9a00); // code0
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write_raw_gdt_entry(GDT_SELECTOR_CODE3, 0x0000ffff, 0x00affa00); // code3
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write_raw_gdt_entry(GDT_SELECTOR_DATA3, 0x0000ffff, 0x008ff200); // data3
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#endif
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#if ARCH(I386)
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@ -115,8 +115,13 @@ u32 Processor::init_context(Thread& thread, bool leave_crit)
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iretframe.rflags = regs.rflags;
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iretframe.rip = regs.rip;
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iretframe.cs = regs.cs;
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iretframe.userspace_rsp = kernel_stack_top;
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iretframe.userspace_ss = 0;
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if (return_to_user) {
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iretframe.userspace_rsp = regs.rsp;
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iretframe.userspace_ss = GDT_SELECTOR_DATA3 | 3;
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} else {
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iretframe.userspace_rsp = kernel_stack_top;
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iretframe.userspace_ss = 0;
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}
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// make space for a trap frame
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stack_top -= sizeof(TrapFrame);
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@ -95,7 +95,7 @@ PageDirectory::PageDirectory(const RangeAllocator* parent_range_allocator)
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#if ARCH(X86_64)
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{
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auto& table = *(PageDirectoryPointerTable*)MM.quickmap_page(*m_pml4t);
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table.raw[0] = (FlatPtr)m_directory_table->paddr().as_ptr() | 3;
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table.raw[0] = (FlatPtr)m_directory_table->paddr().as_ptr() | 7;
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MM.unquickmap_page();
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}
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#endif
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@ -108,10 +108,10 @@ PageDirectory::PageDirectory(const RangeAllocator* parent_range_allocator)
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table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 1;
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table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 1;
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#else
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table.raw[0] = (FlatPtr)m_directory_pages[0]->paddr().as_ptr() | 3;
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table.raw[1] = (FlatPtr)m_directory_pages[1]->paddr().as_ptr() | 3;
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table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 3;
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table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 3;
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table.raw[0] = (FlatPtr)m_directory_pages[0]->paddr().as_ptr() | 7;
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table.raw[1] = (FlatPtr)m_directory_pages[1]->paddr().as_ptr() | 7;
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table.raw[2] = (FlatPtr)m_directory_pages[2]->paddr().as_ptr() | 7;
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table.raw[3] = (FlatPtr)m_directory_pages[3]->paddr().as_ptr() | 7;
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#endif
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// 2 ** MAXPHYADDR - 1
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