048703bb5c
[ Upstream commit be140f1732b523947425aaafbe2e37b41b622d96 ] There is code that builds with calls to IO accessors even when CONFIG_PCI=n, but the actual calls are guarded by runtime checks. If not those calls would be faulting, because the page at virtual address zero is (usually) not mapped into the kernel. As Arnd pointed out, it is possible a large port value could cause the address to be above mmap_min_addr which would then access userspace, which would be a bug. To avoid any such issues, set _IO_BASE to POISON_POINTER_DELTA. That is a value chosen to point into unmapped space between the kernel and userspace, so any access will always fault. Note that on 32-bit POISON_POINTER_DELTA is 0, so the patch only has an effect on 64-bit. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20240503075619.394467-2-mpe@ellerman.id.au 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.