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Message-ID: <e2beec0b-22d3-91bd-c57c-8c8ad2137406@amd.com>
Date: Fri, 4 Nov 2022 13:21:30 -0500
From: "Limonciello, Mario" <mario.limonciello@....com>
To: Evgeniy Baskov <baskov@...ras.ru>,
Ard Biesheuvel <ardb@...nel.org>,
Peter Jones <pjones@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Alexey Khoroshilov <khoroshilov@...ras.ru>,
lvc-project@...uxtesting.org, x86@...nel.org,
linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 00/23] x86_64: Improvements at compressed kernel stage
On 10/25/2022 09:12, 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.
>
> 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.
>
> Changes in v2:
> * Fix spelling.
> * Rebase code to current master.
> * Split huge patches into smaller ones.
> * Remove unneeded forward declarations.
> * Make direct extraction unconditional.
> * Also make it work for x86_32.
> * Reduce lower limit of KASLR to 64M.
> * Make callback interface more logically consistent.
> * Actually declare callbacks structure before using it.
> * Mention effect on x86_32 in commit message of
> "x86/build: Remove RWX sections and align on 4KB".
> * Clarify commit message of
> "x86/boot: Increase boot page table size".
> * Remove "startup32_" prefix on startup32_enable_nx_if_supported.
> * Move linker generated sections outside of function scope.
> * Drop some unintended changes.
> * Drop generating 2 reloc entries.
> (as I've misread the documentation and there's no need for this change.)
> * Set has_nx from enable_nx_if_supported correctly.
> * Move ELF header check to build time.
> * Set WP at the same time as PG in trampoline code,
> as it is more logically consistent.
> * Put x86-specific EFISTUB definitions in x86-stub.h header.
> * Catch presence of ELF segments violating W^X during build.
> * Move PE definitions from build.c to a new header file.
> * Fix generation of PE '.compat' section.
>
> I decided to keep protection of compressed kernel blob and '.rodata'
> separate from '.text' for now, since it does not really have a lot
> of overhead.
>
> Otherwise, all comments on v1 seems to be addressed. Please also apply
> Peter's patch [6] on top of this series.
>
> Patch "x86/boot: Support 4KB pages for identity mapping" needs review
> from x86/mm team.
>
> [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
> [6] https://lkml.org/lkml/2022/10/18/1178
>
> Evgeniy Baskov (23):
> 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/build: Check W^X of vmlinux during build
> 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: Make kernel_add_identity_map() a pointer
> x86/boot: Split trampoline and pt init code
> x86/boot: Add EFI kernel extraction interface
> efi/x86: Support extracting kernel from libstub
> x86/boot: Reduce lower limit of physical KASLR
> x86/boot: Reduce size of the DOS stub
> tools/include: Add simplified version of pe.h
> x86/build: Cleanup tools/build.c
> x86/build: Make generated PE more spec compliant
> efi/x86: Explicitly set sections memory attributes
> efi/libstub: Add memory attribute protocol definitions
> efi/libstub: Use memory attribute protocol
>
> arch/x86/boot/Makefile | 2 +-
> arch/x86/boot/compressed/Makefile | 8 +-
> arch/x86/boot/compressed/acpi.c | 21 +-
> arch/x86/boot/compressed/efi.c | 19 +-
> arch/x86/boot/compressed/head_32.S | 44 +-
> arch/x86/boot/compressed/head_64.S | 76 ++-
> arch/x86/boot/compressed/ident_map_64.c | 122 ++--
> arch/x86/boot/compressed/kaslr.c | 8 +-
> arch/x86/boot/compressed/misc.c | 279 ++++-----
> arch/x86/boot/compressed/misc.h | 23 +-
> arch/x86/boot/compressed/pgtable.h | 20 -
> arch/x86/boot/compressed/pgtable_64.c | 75 ++-
> arch/x86/boot/compressed/putstr.c | 130 ++++
> 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 | 573 +++++++++++-------
> 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 | 27 +
> arch/x86/include/asm/shared/pgtable.h | 29 +
> arch/x86/kernel/vmlinux.lds.S | 15 +-
> arch/x86/mm/ident_map.c | 185 +++++-
> drivers/firmware/efi/Kconfig | 2 +
> drivers/firmware/efi/libstub/Makefile | 2 +-
> drivers/firmware/efi/libstub/efistub.h | 26 +
> drivers/firmware/efi/libstub/mem.c | 190 ++++++
> .../firmware/efi/libstub/x86-extract-direct.c | 204 +++++++
> drivers/firmware/efi/libstub/x86-stub.c | 231 ++-----
> drivers/firmware/efi/libstub/x86-stub.h | 11 +
> include/linux/efi.h | 1 +
> tools/include/linux/pe.h | 150 +++++
> 33 files changed, 1848 insertions(+), 781 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
> create mode 100644 drivers/firmware/efi/libstub/x86-stub.h
> create mode 100644 tools/include/linux/pe.h
>
Hi,
I was talking to Peter Jones recently about what was still missing for
NX support in the kernel and he pointed me at this series.
So I had a try with this series on top of:
ee6050c8af96 ("Merge tag 'ata-6.1-rc4' of
git://git.kernel.org/pub/scm/linux/kernel/git/dlemoal/libata")
Unfortunately I can't boot the system with this series applied.
This is not on a system that enforces NX pre-boot (but that was my goal
after I could prove booting on something that doesn't).
I didn't apply Peter's patch 6 you referenced in your cover letter, but
I don't expect that's the reason for the failure.
I get:
"Failed to allocate space for tmp_cmdline"
-- System Halted
This is early enough [1] that I don't have anything else output to a
serial log from the kernel.
https://github.com/torvalds/linux/blob/d4013bc4d49f6da8178a340348369bb9920225c9/arch/x86/boot/compressed/kaslr.c#L268
Since this is only in the kaslr path, I tried to turn that off with
'nokaslr' on the kernel command line.
I then get a failure of:
"Out of memory while allocating zstd_dctx"
-- System Halted
This kernel was booted from the following path:
-> Insyde BIOS
--> shim (from Fedora 36 repository)
---> GRUB (from Peter for Fedora 36 w/ some level NX support)
----> kernel binary (self-built)
The BIOS on this system doesn't validate NX, but also the shim binary
did not have the NX bit set in the PE header.
Your cover letter referenced CONFIG_EFI_STUB_EXTRACT_DIRECT but I didn't
find this option in the series. I also tried both with
CONFIG_EFI_DXE_MEM_ATTRIBUTES=y or unset, same result.
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