Commit 12792064 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Borislav Petkov (AMD)
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x86/decompressor: Avoid magic offsets for EFI handover entrypoint 



The native 32-bit or 64-bit EFI handover protocol entrypoint offset
relative to the respective startup_32/64 address is described in
boot_params as handover_offset, so that the special Linux/x86 aware EFI
loader can find it there.

When mixed mode is enabled, this single field has to describe this
offset for both the 32-bit and 64-bit entrypoints, so their respective
relative offsets have to be identical. Given that startup_32 and
startup_64 are 0x200 bytes apart, and the EFI handover entrypoint
resides at a fixed offset, the 32-bit and 64-bit versions of those
entrypoints must be exactly 0x200 bytes apart as well.

Currently, hard-coded fixed offsets are used to ensure this, but it is
sufficient to emit the 64-bit entrypoint 0x200 bytes after the 32-bit
one, wherever it happens to reside. This allows this code (which is now
EFI mixed mode specific) to be moved into efi_mixed.S and out of the
startup code in head_64.S.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-6-ardb@kernel.org
parent df9215f1

arch/x86/boot/compressed/efi_mixed.S

+19 −1
Original line number Diff line number Diff line
@@ -140,6 +140,16 @@ SYM_FUNC_START(__efi64_thunk) 
SYM_FUNC_END(__efi64_thunk)



	.code32

#ifdef CONFIG_EFI_HANDOVER_PROTOCOL

SYM_FUNC_START(efi32_stub_entry)

	add	$0x4, %esp		/* Discard return address */

	popl	%ecx

	popl	%edx

	popl	%esi

	jmp	efi32_entry

SYM_FUNC_END(efi32_stub_entry)

#endif



/*

 * EFI service pointer must be in %edi.

 *
@@ -220,7 +230,7 @@ SYM_FUNC_END(efi_enter32) 
 * stub may still exit and return to the firmware using the Exit() EFI boot

 * service.]

 */

SYM_FUNC_START(efi32_entry)

SYM_FUNC_START_LOCAL(efi32_entry)

	call	1f

1:	pop	%ebx
@@ -320,6 +330,14 @@ SYM_FUNC_START(efi32_pe_entry) 
	RET

SYM_FUNC_END(efi32_pe_entry)



#ifdef CONFIG_EFI_HANDOVER_PROTOCOL

	.org	efi32_stub_entry + 0x200

	.code64

SYM_FUNC_START_NOALIGN(efi64_stub_entry)

	jmp	efi_stub_entry

SYM_FUNC_END(efi64_stub_entry)

#endif



	.section ".rodata"

	/* EFI loaded image protocol GUID */

	.balign 4

arch/x86/boot/compressed/head_64.S

+0 −18
Original line number Diff line number Diff line
@@ -294,17 +294,6 @@ SYM_FUNC_START(startup_32) 
	lret

SYM_FUNC_END(startup_32)



#if IS_ENABLED(CONFIG_EFI_MIXED) && IS_ENABLED(CONFIG_EFI_HANDOVER_PROTOCOL)

	.org 0x190

SYM_FUNC_START(efi32_stub_entry)

	add	$0x4, %esp		/* Discard return address */

	popl	%ecx

	popl	%edx

	popl	%esi

	jmp	efi32_entry

SYM_FUNC_END(efi32_stub_entry)

#endif



	.code64

	.org 0x200

SYM_CODE_START(startup_64)
@@ -542,13 +531,6 @@ trampoline_return: 
	jmp	*%rax

SYM_CODE_END(startup_64)



#if IS_ENABLED(CONFIG_EFI_MIXED) && IS_ENABLED(CONFIG_EFI_HANDOVER_PROTOCOL)

	.org 0x390

SYM_FUNC_START(efi64_stub_entry)

	jmp	efi_stub_entry

SYM_FUNC_END(efi64_stub_entry)

#endif



	.text

SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)