Commit 95b39596 authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

arm64/efi: efistub: jump to 'stext' directly, not through the header

After the EFI stub has done its business, it jumps into the kernel by
branching to offset #0 of the loaded Image, which is where it expects
to find the header containing a 'branch to stext' instruction.

However, the UEFI spec 2.1.1 states the following regarding PE/COFF
image loading:
"A UEFI image is loaded into memory through the LoadImage() Boot
Service. This service loads an image with a PE32+ format into memory.
This PE32+ loader is required to load all sections of the PE32+ image
into memory."

In other words, it is /not/ required to load parts of the image that are
not covered by a PE/COFF section, so it may not have loaded the header
at the expected offset, as it is not covered by any PE/COFF section.

So instead, jump to 'stext' directly, which is at the base of the
PE/COFF .text section, by supplying a symbol 'stext_offset' to
efi-entry.o which contains the relative offset of stext into the Image.
Also replace other open coded calculations of the same value with a
reference to 'stext_offset'
Acked-by: default avatarMark Rutland <>
Acked-by: default avatarRoy Franz <>
Signed-off-by: default avatarArd Biesheuvel <>
parent cac7f242
......@@ -61,7 +61,8 @@ ENTRY(efi_stub_entry)
mov x20, x0 // DTB address
ldr x0, [sp, #16] // relocated _text address
mov x21, x0
ldr x21, =stext_offset
add x21, x0, x21
* Flush dcache covering current runtime addresses
......@@ -132,6 +132,8 @@ efi_head:
.globl stext_offset
.set stext_offset, stext - efi_head
.align 3
.ascii "PE"
......@@ -155,7 +157,7 @@ optional_header:
.long 0 // SizeOfInitializedData
.long 0 // SizeOfUninitializedData
.long efi_stub_entry - efi_head // AddressOfEntryPoint
.long stext - efi_head // BaseOfCode
.long stext_offset // BaseOfCode
.quad 0 // ImageBase
......@@ -172,7 +174,7 @@ extra_header_fields:
.long _end - efi_head // SizeOfImage
// Everything before the kernel image is considered part of the header
.long stext - efi_head // SizeOfHeaders
.long stext_offset // SizeOfHeaders
.long 0 // CheckSum
.short 0xa // Subsystem (EFI application)
.short 0 // DllCharacteristics
......@@ -217,9 +219,9 @@ section_table:
.byte 0
.byte 0 // end of 0 padding of section name
.long _end - stext // VirtualSize
.long stext - efi_head // VirtualAddress
.long stext_offset // VirtualAddress
.long _edata - stext // SizeOfRawData
.long stext - efi_head // PointerToRawData
.long stext_offset // PointerToRawData
.long 0 // PointerToRelocations (0 for executables)
.long 0 // PointerToLineNumbers (0 for executables)
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