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

Marvin Häuser
2023-08-18T14:35:49Z

Hi Ard,

Thanks for your effort! Not sure what the documentation policies are, but might it be worth mentioning that we cannot have .rdata at this time, because current-gen EFI will map it as RW?

Best regards,
Marvin

> On Aug 18, 2023, at 15:45, Ard Biesheuvel <ardb@kernel.org> wrote:
> ﻿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