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: 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

diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compressed/efi_mixed.S
index dcc562c..9308b59 100644 (file)
--- a/arch/x86/boot/compressed/efi_mixed.S
+++ b/arch/x86/boot/compressed/efi_mixed.S
@@ -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

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index e688020..a3f764d 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -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)