[PATCH 15/17] x86/boot: Split off PE/COFF .data section

Ard Biesheuvel
2023-08-18T13:46:25Z

Describe the code and data of the decompressor binary using separate
.text and .data PE/COFF sections, so that we will be able to map them
using restricted permissions once we increase the section and file
alignment sufficiently. This avoids the need for memory mappings that
are writable and executable at the same time, which is something that
is best avoided for security reasons.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/Makefile | 2 +-
arch/x86/boot/header.S | 19 +++++++++++++++----
2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index b26e30a2d865f72d..50c50fce646e2417 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -90,7 +90,7 @@ $(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE

SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))

-sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_edata\|z_.*\)$$/\#define ZO_\2 0x\1/p'
+sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_e\?data\|z_.*\)$$/\#define ZO_\2 0x\1/p'

quiet_cmd_zoffset = ZOFFSET $@
cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index ccfb7a7d8c29275e..25dda40dacb52292 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -79,9 +79,9 @@ optional_header:
.byte 0x02 # MajorLinkerVersion
.byte 0x14 # MinorLinkerVersion

- .long setup_size + ZO__end - 0x200 # SizeOfCode
+ .long ZO__data # SizeOfCode

- .long 0 # SizeOfInitializedData
+ .long ZO__end - ZO__data # SizeOfInitializedData
.long 0 # SizeOfUninitializedData

.long setup_size + ZO_efi_pe_entry # AddressOfEntryPoint
@@ -182,9 +182,9 @@ section_table:
.byte 0
.byte 0
.byte 0
- .long ZO__end
+ .long ZO__data
.long setup_size
- .long ZO__edata # Size of initialized data
+ .long ZO__data # Size of initialized data
# on disk
.long setup_size
.long 0 # PointerToRelocations
@@ -195,6 +195,17 @@ section_table:
IMAGE_SCN_MEM_READ | \
IMAGE_SCN_MEM_EXECUTE # Characteristics

+ .ascii ".data\0\0\0"
+ .long ZO__end - ZO__data # VirtualSize
+ .long setup_size + ZO__data # VirtualAddress
+ .long ZO__edata - ZO__data # SizeOfRawData
+ .long setup_size + ZO__data # PointerToRawData
+
+ .long 0, 0, 0
+ .long IMAGE_SCN_CNT_INITIALIZED_DATA | \
+ IMAGE_SCN_MEM_READ | \
+ IMAGE_SCN_MEM_WRITE # Characteristics
+
.set section_count, (. - section_table) / 40
#endif /* CONFIG_EFI_STUB */

--
2.39.2