Commit 630f337f authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Borislav Petkov
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x86/boot/compressed: Simplify IDT/GDT preserve/restore in the EFI thunk 



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

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-9-ardb@kernel.org
parent 4b520162

arch/x86/boot/compressed/efi_mixed.S

+7 −13
Original line number Diff line number Diff line
@@ -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