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x86/boot/compressed: Simplify IDT/GDT preserve/restore in the EFI thunk

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Tweak the asm and remove some redundant instructions. While at it,
fix the associated comment for style and correctness.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-9-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2022-11-22 17:10:08 +01:00 committed by Borislav Petkov
parent 4b52016247
commit 630f337f0c
1 changed files with 7 additions and 13 deletions
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20
arch/x86/boot/compressed/efi_mixed.S
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@ -96,24 +96,20 @@ SYM_FUNC_START(__efi64_thunk)
leaq 0x20(%rsp), %rbx
sgdt (%rbx)
addq $16, %rbx
sidt (%rbx)
sidt 16(%rbx)
leaq 1f(%rip), %rbp
/*
* Switch to IDT and GDT with 32-bit segments. This is the firmware GDT
* and IDT that was installed when the kernel started executing. The
* pointers were saved by the efi32_entry() routine below.
* Switch to IDT and GDT with 32-bit segments. These are the firmware
* GDT and IDT that were installed when the kernel started executing.
* The pointers were saved by the efi32_entry() routine below.
*
* Pass the saved DS selector to the 32-bit code, and use far return to
* restore the saved CS selector.
*/
leaq efi32_boot_idt(%rip), %rax
lidt (%rax)
leaq efi32_boot_gdt(%rip), %rax
lgdt (%rax)
lidt efi32_boot_idt(%rip)
lgdt efi32_boot_gdt(%rip)
movzwl efi32_boot_ds(%rip), %edx
movzwq efi32_boot_cs(%rip), %rax
@ -187,9 +183,7 @@ SYM_FUNC_START_LOCAL(efi_enter32)
*/
cli
lidtl (%ebx)
subl $16, %ebx
lidtl 16(%ebx)
lgdtl (%ebx)
movl %cr4, %eax