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x86/decompressor: Avoid magic offsets for EFI handover entrypoint

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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: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-6-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2023-08-07 18:27:02 +02:00 committed by Borislav Petkov (AMD)
parent df9215f152
commit 1279206458
2 changed files with 19 additions and 19 deletions
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20
arch/x86/boot/compressed/efi_mixed.S
View File

@ -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

18
arch/x86/boot/compressed/head_64.S
View File

@ -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)