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[ Upstream commit 84361123413efc84b06f3441c6c827b95d902732 ]
When transitioning from 5-level to 4-level paging, the existing code
incorrectly accesses page table entries by directly dereferencing CR3 and
applying PAGE_MASK. This approach has several issues:
- __native_read_cr3() returns the raw CR3 register value, which on x86_64
includes not just the physical address but also flags Bits above the
physical address width of the system (i.e. above __PHYSICAL_MASK_SHIFT) are
also not masked.
- The pgd value is masked by PAGE_SIZE which doesn't take into account the
higher bits such as _PAGE_BIT_NOPTISHADOW.
Replace this with proper accessor functions:
- native_read_cr3_pa(): Uses CR3_ADDR_MASK to additionally mask metadata out
of CR3 (like SME or LAM bits). All remaining bits are real address bits or
reserved and must be 0.
- mask pgd value with PTE_PFN_MASK instead of PAGE_MASK, accounting for flags
above bit 51 (_PAGE_BIT_NOPTISHADOW in particular). Bits below 51, but above
the max physical address are reserved and must be 0.
Fixes: cb1c9e02b0 ("x86/efistub: Perform 4/5 level paging switch from the stub")
Reported-by: Michael van der Westhuizen <rmikey@meta.com>
Reported-by: Tobias Fleig <tfleig@meta.com>
Co-developed-by: Kiryl Shutsemau <kas@kernel.org>
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://patch.msgid.link/20251103141002.2280812-3-usamaarif642@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
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 Restructured Text 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.