[PATCH v2] arm64/efi: efistub: jump to 'stext' directly, not through the header

Ard Biesheuvel
2014-07-15T10:58:06Z

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 header is not covered by any PE/COFF section, so the header may
not actually be loaded at the expected offset. 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'

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
arch/arm64/kernel/efi-entry.S | 3 ++-
arch/arm64/kernel/head.S | 10 ++++++----
2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
index 619b1dd7bcde..a0016d3a17da 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -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
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index a2c1195abb7f..78ddae28b090 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -137,6 +137,8 @@ efi_head:
#endif

#ifdef CONFIG_EFI
+ .globl stext_offset
+ .set stext_offset, stext - efi_head
.align 3
pe_header:
.ascii "PE"
@@ -160,7 +162,7 @@ optional_header:
.long 0 // SizeOfInitializedData
.long 0 // SizeOfUninitializedData
.long efi_stub_entry - efi_head // AddressOfEntryPoint
- .long stext - efi_head // BaseOfCode
+ .long stext_offset // BaseOfCode

extra_header_fields:
.quad 0 // ImageBase
@@ -177,7 +179,7 @@ extra_header_fields:
.long _edata - 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
@@ -222,9 +224,9 @@ section_table:
.byte 0
.byte 0 // end of 0 padding of section name
.long _edata - 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)
--
1.8.3.2