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[00/16] x86_64: Improvements at compressed kernel stage

Message ID cover.1662459668.git.baskov@ispras.ru
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Series x86_64: Improvements at compressed kernel stage | expand

Message

Evgeniy Baskov Sept. 6, 2022, 10:41 a.m. UTC 
This patchset is aimed
* to improve UEFI compatibility of compressed kernel code for x86_64
* to setup proper memory access attributes for code and rodata sections
* to implement W^X protection policy throughout the whole execution 
  of compressed kernel for EFISTUB code path. 

Kernel is made to be more compatible with PE image specification [3],
allowing it to be successfully loaded by stricter PE loader
implementations like the one from [2]. There is at least one
known implementation that uses that loader in production [4].
There are also ongoing efforts to upstream these changes.

Also the patchset adds EFI_MEMORY_ATTTRIBUTE_PROTOCOL, included into
EFI specification since version 2.10, as a better alternative to
using DXE services for memory protection attributes manipulation,
since it is defined by the UEFI specification itself and not UEFI PI
specification. This protocol is not widely available so the code
using DXE services is kept in place as a fallback in case specific
implementation does not support the new protocol.
One of EFI implementations that already support
EFI_MEMORY_ATTTRIBUTE_PROTOCOL is Microsoft Project Mu [5].
 
Kernel image generation tool (tools/build.c) is refactored as a part
of changes that makes PE image more compatible.
   
The patchset implements memory protection for compressed kernel
code while executing both inside EFI boot services and outside of
them. For EFISTUB code path W^X protection policy is maintained
throughout the whole execution of compressed kernel. The latter
is achieved by extracting the kernel directly from EFI environment
and jumping to it's head immediately after exiting EFI boot services.
As a side effect of this change one page table rebuild and a copy of
the kernel image is removed.

Direct extraction can be toggled using CONFIG_EFI_STUB_EXTRACT_DIRECT.
Memory protection inside EFI environment is controlled by the
CONFIG_DXE_MEM_ATTRIBUTES option, although with these patches this
option also control the use EFI_MEMORY_ATTTRIBUTE_PROTOCOL and memory
protection attributes of PE sections and not only DXE services as the
name might suggest.

[1] https://lkml.org/lkml/2022/8/1/1314
[2] https://github.com/acidanthera/audk/tree/secure_pe
[3] https://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/pecoff_v83.docx
[4] https://www.ispras.ru/en/technologies/asperitas/
[5] https://github.com/microsoft/mu_tiano_platforms

Evgeniy Baskov (16):
  x86/boot: Align vmlinuz sections on page size
  x86/build: Remove RWX sections and align on 4KB
  x86/boot: Set cr0 to known state in trampoline
  x86/boot: Increase boot page table size
  x86/boot: Support 4KB pages for identity mapping
  x86/boot: Setup memory protection for bzImage code
  x86/boot: Map memory explicitly
  x86/boot: Remove mapping from page fault handler
  efi/libstub: Move helper function to related file
  x86/boot: Make console interface more abstract
  x86/boot: Split trampoline and pt init code
  x86/boot: Add EFI kernel extraction interface
  efi/x86: Support extracting kernel from libstub
  x86/build: Make generated PE more spec compliant
  efi/libstub: Add memory attribute protocol definitions
  efi/libstub: Use memory attribute protocol

 arch/x86/boot/Makefile                        |   2 +-
 arch/x86/boot/compressed/Makefile             |   2 +-
 arch/x86/boot/compressed/acpi.c               |  21 +-
 arch/x86/boot/compressed/efi.c                |  19 +-
 arch/x86/boot/compressed/head_32.S            |   9 +-
 arch/x86/boot/compressed/head_64.S            |  77 ++-
 arch/x86/boot/compressed/ident_map_64.c       | 129 ++--
 arch/x86/boot/compressed/kaslr.c              |   4 +
 arch/x86/boot/compressed/misc.c               | 255 ++++----
 arch/x86/boot/compressed/misc.h               |  25 +-
 arch/x86/boot/compressed/pgtable.h            |  20 -
 arch/x86/boot/compressed/pgtable_64.c         |  75 ++-
 arch/x86/boot/compressed/putstr.c             | 133 ++++
 arch/x86/boot/compressed/sev.c                |   6 +-
 arch/x86/boot/compressed/vmlinux.lds.S        |   6 +
 arch/x86/boot/header.S                        | 110 +---
 arch/x86/boot/tools/build.c                   | 575 ++++++++++++------
 arch/x86/include/asm/boot.h                   |  26 +-
 arch/x86/include/asm/efi.h                    |   7 +
 arch/x86/include/asm/init.h                   |   1 +
 arch/x86/include/asm/shared/extract.h         |  25 +
 arch/x86/include/asm/shared/pgtable.h         |  29 +
 arch/x86/kernel/vmlinux.lds.S                 |  15 +-
 arch/x86/mm/ident_map.c                       | 186 +++++-
 drivers/firmware/efi/Kconfig                  |  14 +
 drivers/firmware/efi/libstub/Makefile         |   1 +
 drivers/firmware/efi/libstub/efistub.h        |  31 +
 drivers/firmware/efi/libstub/mem.c            | 189 ++++++
 .../firmware/efi/libstub/x86-extract-direct.c | 220 +++++++
 drivers/firmware/efi/libstub/x86-stub.c       | 172 +++---
 include/linux/efi.h                           |   1 +
 31 files changed, 1701 insertions(+), 684 deletions(-)
 delete mode 100644 arch/x86/boot/compressed/pgtable.h
 create mode 100644 arch/x86/boot/compressed/putstr.c
 create mode 100644 arch/x86/include/asm/shared/extract.h
 create mode 100644 arch/x86/include/asm/shared/pgtable.h
 create mode 100644 drivers/firmware/efi/libstub/x86-extract-direct.c

Comments

Peter Jones Oct. 18, 2022, 9:04 p.m. UTC | #1 
On Tue, Sep 06, 2022 at 01:41:04PM +0300, Evgeniy Baskov wrote:
> This patchset is aimed
> * to improve UEFI compatibility of compressed kernel code for x86_64
> * to setup proper memory access attributes for code and rodata sections
> * to implement W^X protection policy throughout the whole execution 
>   of compressed kernel for EFISTUB code path. 

Hi Evgeniy,

I've tested this set of patches with the Mu firmware that supports the W^X
feature and a modified bootloader to also support it, and also with an
existing firmware and the grub2 build in fedora 36.  On the firmware
without W^X support, this all works for me.  With W^X support, it works
so long as I use CONFIG_EFI_STUB_EXTRACT_DIRECT, though I still need
some changes in grub's loader.  IMO that's a big step forward.

I can't currently make it work with W^X enabled but without direct
extraction, and I'm still investigating why not, but I figured I'd give
you a heads up.
Evgeniy Baskov Oct. 20, 2022, 11:05 a.m. UTC | #2 
On 2022-10-19 00:04, Peter Jones wrote:
> On Tue, Sep 06, 2022 at 01:41:04PM +0300, Evgeniy Baskov wrote:
>> This patchset is aimed
>> * to improve UEFI compatibility of compressed kernel code for x86_64
>> * to setup proper memory access attributes for code and rodata 
>> sections
>> * to implement W^X protection policy throughout the whole execution
>>   of compressed kernel for EFISTUB code path.
> 
> Hi Evgeniy,
> 
> I've tested this set of patches with the Mu firmware that supports the 
> W^X
> feature and a modified bootloader to also support it, and also with an
> existing firmware and the grub2 build in fedora 36.  On the firmware
> without W^X support, this all works for me.  With W^X support, it works
> so long as I use CONFIG_EFI_STUB_EXTRACT_DIRECT, though I still need
> some changes in grub's loader.  IMO that's a big step forward.
> 
> I can't currently make it work with W^X enabled but without direct
> extraction, and I'm still investigating why not, but I figured I'd give
> you a heads up.

Hi Peter,

Thank you for testing!

Without direct extraction enabled this patch set does not implement 
total W^X
and needs to allocate RWX memory regions, since it should go through 
common
code path that relocates kernel. So if the firmware does not allow 
allocating
RWX regions, it might prevent the kernel from booting, I think. I will 
look
into that problem soon and let you know it I find anything.

Thanks,
Evgeniy Baskov