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New processors that support Shadow Stack regard Write=0,Dirty=1 PTEs as shadow stack pages. In normal cases, it can be helpful to create Write=1 PTEs as also Dirty=1 if HW dirty tracking is not needed, because if the Dirty bit is not already set the CPU has to set Dirty=1 when the memory gets written to. This creates additional work for the CPU. So traditional wisdom was to simply set the Dirty bit whenever you didn't care about it. However, it was never really very helpful for read-only kernel memory. When CR4.CET=1 and IA32_S_CET.SH_STK_EN=1, some instructions can write to such supervisor memory. The kernel does not set IA32_S_CET.SH_STK_EN, so avoiding kernel Write=0,Dirty=1 memory is not strictly needed for any functional reason. But having Write=0,Dirty=1 kernel memory doesn't have any functional benefit either, so to reduce ambiguity between shadow stack and regular Write=0 pages, remove Dirty=1 from any kernel Write=0 PTEs. Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Kees Cook <keescook@chromium.org> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Tested-by: Pengfei Xu <pengfei.xu@intel.com> Tested-by: John Allen <john.allen@amd.com> Tested-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/all/20230613001108.3040476-14-rick.p.edgecombe%40intel.com
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.