Commit ac3c76cc authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
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efi/libstub/x86: Use mandatory 16-byte stack alignment in mixed mode 



Reduce the stack frame of the EFI stub's mixed mode thunk routine by
8 bytes, by moving the GDT and return addresses to EBP and EBX, which
we need to preserve anyway, since their top halves will be cleared by
the call into 32-bit firmware code. Doing so results in the UEFI code
being entered with a 16 byte aligned stack, as mandated by the UEFI
spec, fixing the last occurrence in the 64-bit kernel where we violate
this requirement.

Also, move the saved GDT from a global variable to an unused part of the
stack frame, and touch up some other parts of the code.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200113172245.27925-3-ardb@kernel.org
parent 796eb8d2

arch/x86/boot/compressed/efi_thunk_64.S

+13 −33
Original line number Diff line number Diff line
@@ -27,12 +27,9 @@ SYM_FUNC_START(__efi64_thunk) 
	push	%rbp

	push	%rbx



	subq	$8, %rsp

	leaq	1f(%rip), %rax

	movl	%eax, 4(%rsp)

	leaq	efi_gdt64(%rip), %rax

	movl	%eax, (%rsp)

	movl	%eax, 2(%rax)		/* Fixup the gdt base address */

	leaq	1f(%rip), %rbp

	leaq	efi_gdt64(%rip), %rbx

	movl	%ebx, 2(%rbx)		/* Fixup the gdt base address */



	movl	%ds, %eax

	push	%rax
@@ -48,12 +45,10 @@ SYM_FUNC_START(__efi64_thunk) 
	movl	%esi, 0x0(%rsp)

	movl	%edx, 0x4(%rsp)

	movl	%ecx, 0x8(%rsp)

	movq	%r8, %rsi

	movl	%esi, 0xc(%rsp)

	movq	%r9, %rsi

	movl	%esi,  0x10(%rsp)

	movl	%r8d, 0xc(%rsp)

	movl	%r9d, 0x10(%rsp)



	sgdt	save_gdt(%rip)

	sgdt	0x14(%rsp)



	/*

	 * Switch to gdt with 32-bit segments. This is the firmware GDT
@@ -68,11 +63,10 @@ SYM_FUNC_START(__efi64_thunk) 
	pushq	%rax

	lretq



1:	addq	$32, %rsp

1:	lgdt	0x14(%rsp)

	addq	$32, %rsp

	movq	%rdi, %rax



	lgdt	save_gdt(%rip)



	pop	%rbx

	movl	%ebx, %ss

	pop	%rbx
@@ -83,15 +77,9 @@ SYM_FUNC_START(__efi64_thunk) 
	/*

	 * Convert 32-bit status code into 64-bit.

	 */

	test	%rax, %rax

	jz	1f

	movl	%eax, %ecx

	andl	$0x0fffffff, %ecx

	andl	$0xf0000000, %eax

	shl	$32, %rax

	or	%rcx, %rax

1:

	addq	$8, %rsp

	roll	$1, %eax

	rorq	$1, %rax



	pop	%rbx

	pop	%rbp

	ret
@@ -135,9 +123,7 @@ SYM_FUNC_START_LOCAL(efi_enter32) 
	 */

	cli



	movl	56(%esp), %eax

	movl	%eax, 2(%eax)

	lgdtl	(%eax)

	lgdtl	(%ebx)



	movl	%cr4, %eax

	btsl	$(X86_CR4_PAE_BIT), %eax
@@ -154,9 +140,8 @@ SYM_FUNC_START_LOCAL(efi_enter32) 
	xorl	%eax, %eax

	lldt	%ax



	movl	60(%esp), %eax

	pushl	$__KERNEL_CS

	pushl	%eax

	pushl	%ebp



	/* Enable paging */

	movl	%cr0, %eax
@@ -172,11 +157,6 @@ SYM_DATA_START(efi32_boot_gdt) 
	.quad	0

SYM_DATA_END(efi32_boot_gdt)



SYM_DATA_START_LOCAL(save_gdt)

	.word	0

	.quad	0

SYM_DATA_END(save_gdt)



SYM_DATA_START(efi_gdt64)

	.word	efi_gdt64_end - efi_gdt64

	.long	0			/* Filled out by user */

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