On 19.03.23 01:15, Rick Edgecombe wrote:
The x86 Control-flow Enforcement Technology (CET) feature includes a new type of memory called shadow stack. This shadow stack memory has some unusual properties, which requires some core mm changes to function properly. One sharp edge is that PTEs that are both Write=0 and Dirty=1 are treated as shadow by the CPU, but this combination used to be created by the kernel on x86. Previous patches have changed the kernel to now avoid creating these PTEs unless they are for shadow stack memory. In case any missed corners of the kernel are still creating PTEs like this for non-shadow stack memory, and to catch any re-introductions of the logic, warn if any shadow stack PTEs (Write=0, Dirty=1) are found in non-shadow stack VMAs when they are being zapped. This won't catch transient cases but should have decent coverage. It will be compiled out when shadow stack is not configured. In order to check if a PTE is shadow stack in core mm code, add two arch breakouts arch_check_zapped_pte/pmd(). This will allow shadow stack specific code to be kept in arch/x86. Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx> Tested-by: John Allen <john.allen@xxxxxxx> Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
