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

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Message-Id: <20230818134422.380032-16-ardb@kernel.org>
Date:   Fri, 18 Aug 2023 15:44:20 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Evgeniy Baskov <baskov@...ras.ru>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Jones <pjones@...hat.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Marvin Häuser <mhaeuser@...teo.de>
Subject: [PATCH 15/17] x86/boot: Split off PE/COFF .data section

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@...nel.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