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Ard Biesheuvel a0025f587c x86/boot/64: Clear most of CR4 in startup_64(), except PAE, MCE and LA57
The early 64-bit boot code must be entered with a 1:1 mapping of the
bootable image, but it cannot operate without a 1:1 mapping of all the
assets in memory that it accesses, and therefore, it creates such
mappings for all known assets upfront, and additional ones on demand
when a page fault happens on a memory address.

These mappings are created with the global bit G set, as the flags used
to create page table descriptors are based on __PAGE_KERNEL_LARGE_EXEC
defined by the core kernel, even though the context where these mappings
are used is very different.

This means that the TLB maintenance carried out by the decompressor is
not sufficient if it is entered with CR4.PGE enabled, which has been
observed to happen with the stage0 bootloader of project Oak. While this
is a dubious practice if no global mappings are being used to begin
with, the decompressor is clearly at fault here for creating global
mappings and not performing the appropriate TLB maintenance.

Since commit:

  f97b67a773 ("x86/decompressor: Only call the trampoline when changing paging levels")

CR4 is no longer modified by the decompressor if no change in the number
of paging levels is needed. Before that, CR4 would always be set to a
consistent value with PGE cleared.

So let's reinstate a simplified version of the original logic to put CR4
into a known state, and preserve the PAE, MCE and LA57 bits, none of
which can be modified freely at this point (PAE and LA57 cannot be
changed while running in long mode, and MCE cannot be cleared when
running under some hypervisors).

This effectively clears PGE and works around the project Oak bug.

Fixes: f97b67a773 ("x86/decompressor: Only call the trampoline when ...")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20240410151354.506098-2-ardb+git@google.com
History 2024-04-11 15:37:17 +02:00
arch x86/boot/64: Clear most of CR4 in startup_64(), except PAE, MCE and LA57 2024-04-11 15:37:17 +02:00
block block-6.9-20240405 2024-04-05 17:04:11 -07:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto This push fixes a regression that broke iwd as well as a divide by 2024-03-25 10:48:23 -07:00
Documentation Devicetree fixes for v6.9, part 1: 2024-04-05 14:07:22 -07:00
drivers Miscellaneous x86 fixes: 2024-04-07 09:33:21 -07:00
fs nfsd-6.9 fixes: 2024-04-06 09:37:50 -07:00
include Linux 6.9-rc3 2024-04-11 15:36:23 +02:00
init init: open output files from cpio unpacking with O_LARGEFILE 2024-04-05 11:21:30 -07:00
io_uring io_uring/kbuf: hold io_buffer_list reference over mmap 2024-04-02 19:03:27 -06:00
ipc sysctl changes for v6.9-rc1 2024-03-18 14:59:13 -07:00
kernel Fix various timer bugs: 2024-04-07 09:20:50 -07:00
lib stackdepot: rename pool_index to pool_index_plus_1 2024-04-05 11:21:31 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm x86/mm/pat: fix VM_PAT handling in COW mappings 2024-04-05 11:21:31 -07:00
net nfsd-6.9 fixes: 2024-04-06 09:37:50 -07:00
rust Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
samples Tracing updates for 6.9: 2024-03-18 15:11:44 -07:00
scripts Four small documentation fixes. 2024-04-02 12:44:09 -07:00
security security: Place security_path_post_mknod() where the original IMA call was 2024-04-03 10:21:32 -07:00
sound ASoC: Fixes for v6.9 2024-04-05 08:48:12 +02:00
tools 8 hotfixes, 3 are cc:stable 2024-04-05 13:30:01 -07:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt KVM Xen and pfncache changes for 6.9: 2024-03-11 10:42:55 -04:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap MAINTAINERS: change vmware.com addresses to broadcom.com 2024-04-05 11:21:31 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Not a ton of stuff happening in the clk framework in this pull request. We got 2024-03-15 11:48:01 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Devicetree fixes for v6.9, part 1: 2024-04-05 14:07:22 -07:00
Makefile Linux 6.9-rc3 2024-04-07 13:22:46 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.