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x86/boot/compressed: Avoid touching ECX in startup32_set_idt_entry()

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commit 6aac80a8da upstream.

Avoid touching register %ecx in startup32_set_idt_entry(), by folding
the MOV, SHL and ORL instructions into a single ORL which no longer
requires a temp register.

This permits ECX to be used as a function argument in a subsequent
patch.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-10-ardb@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ard Biesheuvel
2022-11-22 17:10:09 +01:00
committed by Greg Kroah-Hartman
parent 88035744b9
commit 530a4271b7
1 changed files with 2 additions and 6 deletions
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8
arch/x86/boot/compressed/head_64.S
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@@ -749,7 +749,6 @@ SYM_DATA_END_LABEL(boot32_idt, SYM_L_GLOBAL, boot32_idt_end)
*/
SYM_FUNC_START(startup32_set_idt_entry)
push %ebx
push %ecx
/* IDT entry address to %ebx */
leal rva(boot32_idt)(%ebp), %ebx
@@ -758,10 +757,8 @@ SYM_FUNC_START(startup32_set_idt_entry)
/* Build IDT entry, lower 4 bytes */
movl %eax, %edx
andl $0x0000ffff, %edx # Target code segment offset [15:0]
movl $__KERNEL32_CS, %ecx # Target code segment selector
shl $16, %ecx
orl %ecx, %edx
andl $0x0000ffff, %edx # Target code segment offset [15:0]
orl $(__KERNEL32_CS << 16), %edx # Target code segment selector
/* Store lower 4 bytes to IDT */
movl %edx, (%ebx)
@@ -774,7 +771,6 @@ SYM_FUNC_START(startup32_set_idt_entry)
/* Store upper 4 bytes to IDT */
movl %edx, 4(%ebx)
pop %ecx
pop %ebx
RET
SYM_FUNC_END(startup32_set_idt_entry)