From: Ard Biesheuvel Date: Tue, 22 Nov 2022 16:10:09 +0000 (+0100) Subject: x86/boot/compressed: Avoid touching ECX in startup32_set_idt_entry() X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=530a4271b7ba5776b7f5a67015ae63a3ba3d2348;p=people%2Faperard%2Flinux.git x86/boot/compressed: Avoid touching ECX in startup32_set_idt_entry() commit 6aac80a8da46d70f2ae7ff97c9f45a15c7c9b3ef 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 Signed-off-by: Borislav Petkov Link: https://lore.kernel.org/r/20221122161017.2426828-10-ardb@kernel.org Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 2235c3a13f547..e90cbbb2903d9 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -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)