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

Ard Biesheuvel
2023-09-07T18:22:23Z

On Fri, 18 Aug 2023 at 16:35, Marvin Häuser <mhaeuser@posteo.de> wrote:
>
> 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?
>

Yeah I'll mention this in the next version.

> 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
>