linux-kernel - [PATCH 0/3] x86: Fix kexec 5-level to 4-level paging transition

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251022220755.1026144-1-usamaarif642@gmail.com>
Date: Wed, 22 Oct 2025 23:06:24 +0100
From: Usama Arif <usamaarif642@...il.com>
To: dwmw@...zon.co.uk,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	ardb@...nel.org,
	hpa@...or.com
Cc: x86@...nel.org,
	apopple@...dia.com,
	thuth@...hat.com,
	nik.borisov@...e.com,
	kas@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org,
	kernel-team@...a.com,
	Usama Arif <usamaarif642@...il.com>,
	Michael van der Westhuizen <rmikey@...a.com>,
	Tobias Fleig <tfleig@...a.com>
Subject: [PATCH 0/3] x86: Fix kexec 5-level to 4-level paging transition

This series addresses critical bugs in the kexec path when transitioning
from a kernel using 5-level page tables to one using 4-level page tables.

The root cause is improper handling of PGD entry value during the page level
transition. Specifically p4d value is masked with PAGE_MASK instead of
PTE_PFN_MASK, failing to account for high-order software bits like
_PAGE_BIT_NOPTISHADOW (bit 58).

When bit 58 (_PAGE_BIT_NOPTISHADOW) is set in the source kernel, the target
4-level kernel doesn't recognize it and fails to mask it properly, leading
to kexec failure.

This series fixes the issue in three parts:

Patch 1: Fixes the x86 boot compressed code path by replacing direct CR3
dereferencing with read_cr3_pa() and using PTE_PFN_MASK instead
of PAGE_MASK.

Patch 2: Applies the same fix to the EFI stub code path. (Done in a
separate patch as Fixes tag is different).

Patch 3: Moves _PAGE_BIT_NOPTISHADOW from bit 58 (_PAGE_BIT_SOFTW5) to
bit 9 (_PAGE_BIT_SOFTW1), which is already properly masked by
older kernels. This provides backward compatibility without
requiring patches 1 and 2 to be applied to all existing kernel versions,
which is not feasible for production systems or live patching.

Co-developed-by: Kiryl Shutsemau <kas@...nel.org>
Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
Signed-off-by: Usama Arif <usamaarif642@...il.com>
Reported-by: Michael van der Westhuizen <rmikey@...a.com>
Reported-by: Tobias Fleig <tfleig@...a.com>

The patches are based on aaa9c3550b60d6259d6ea8b1175ade8d1242444e (next-20251022)

Usama Arif (3):
  x86/boot: Fix page table access in 5-level to 4-level paging
    transition
  efi/libstub: Fix page table access in 5-level to 4-level paging
    transition
  x86/mm: Move _PAGE_BIT_NOPTISHADOW from bit 58 to bit 9

 arch/x86/boot/compressed/pgtable_64.c   | 8 +++++---
 arch/x86/include/asm/pgtable_types.h    | 4 ++--
 drivers/firmware/efi/libstub/x86-5lvl.c | 5 ++++-
 3 files changed, 11 insertions(+), 6 deletions(-)

-- 
2.47.3