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The kvmppc_hpte_page_shifts function decodes the actual and base page sizes for a HPTE, returning -1 if it doesn't recognize the page size encoding. This then gets used as a shift amount in various places, which is undefined behaviour. This was reported by Coverity. In fact this should never occur, since we should only get HPTEs in the HPT which have a recognized page size encoding. The only place where this might not be true is in the call to kvmppc_actual_pgsz() near the beginning of kvmppc_do_h_enter(), where we are validating the HPTE value passed in from the guest. So to fix this and eliminate the undefined behaviour, we make kvmppc_hpte_page_shifts return 0 for unrecognized page size encodings, and make kvmppc_actual_pgsz() detect that case and return 0 for the page size, which will then cause kvmppc_do_h_enter() to return an error and refuse to insert any HPTE with an unrecognized page size encoding. To ensure that we don't get undefined behaviour in compute_tlbie_rb(), we take the 4k page size path for any unrecognized page size encoding. This should never be hit in practice because it is only used on HPTE values which have previously been checked for having a recognized page size encoding. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.