[PATCH 6.1 183/215] x86/decompressor: Avoid magic offsets for EFI handover entrypoint

Greg Kroah-Hartman
2024-03-04T21:50:52Z

From: Ard Biesheuvel <ardb+git@google.com>

From: Ard Biesheuvel <ardb@kernel.org>

[ Commit 12792064587623065250069d1df980e2c9ac3e67 upstream ]

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
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/boot/compressed/efi_mixed.S | 20 +++++++++++++++++++-
arch/x86/boot/compressed/head_64.S | 18 ------------------
2 files changed, 19 insertions(+), 19 deletions(-)

--- a/arch/x86/boot/compressed/efi_mixed.S
+++ b/arch/x86/boot/compressed/efi_mixed.S
@@ -146,6 +146,16 @@ 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.
*
@@ -226,7 +236,7 @@ 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

@@ -326,6 +336,14 @@ 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
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -286,17 +286,6 @@ 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)
@@ -474,13 +463,6 @@ SYM_CODE_START(startup_64)
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)