[PATCH 6.1 117/215] x86/boot/compressed: Simplify IDT/GDT preserve/restore in the EFI thunk

Greg Kroah-Hartman
2024-03-04T21:47:22Z

From: Ard Biesheuvel <ardb@kernel.org>

commit 630f337f0c4fd80390e8600adcab31550aea33df upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/boot/compressed/efi_mixed.S | 20 +++++++-------------
1 file changed, 7 insertions(+), 13 deletions(-)

--- a/arch/x86/boot/compressed/efi_mixed.S
+++ b/arch/x86/boot/compressed/efi_mixed.S
@@ -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