1. 27 7月, 2007 1 次提交
  2. 06 2月, 2007 1 次提交
    • G
      [S390] noexec protection · c1821c2e
      Gerald Schaefer 提交于
      This provides a noexec protection on s390 hardware. Our hardware does
      not have any bits left in the pte for a hw noexec bit, so this is a
      different approach using shadow page tables and a special addressing
      mode that allows separate address spaces for code and data.
      
      As a special feature of our "secondary-space" addressing mode, separate
      page tables can be specified for the translation of data addresses
      (storage operands) and instruction addresses. The shadow page table is
      used for the instruction addresses and the standard page table for the
      data addresses.
      The shadow page table is linked to the standard page table by a pointer
      in page->lru.next of the struct page corresponding to the page that
      contains the standard page table (since page->private is not really
      private with the pte_lock and the page table pages are not in the LRU
      list).
      Depending on the software bits of a pte, it is either inserted into
      both page tables or just into the standard (data) page table. Pages of
      a vma that does not have the VM_EXEC bit set get mapped only in the
      data address space. Any try to execute code on such a page will cause a
      page translation exception. The standard reaction to this is a SIGSEGV
      with two exceptions: the two system call opcodes 0x0a77 (sys_sigreturn)
      and 0x0aad (sys_rt_sigreturn) are allowed. They are stored by the
      kernel to the signal stack frame. Unfortunately, the signal return
      mechanism cannot be modified to use an SA_RESTORER because the
      exception unwinding code depends on the system call opcode stored
      behind the signal stack frame.
      
      This feature requires that user space is executed in secondary-space
      mode and the kernel in home-space mode, which means that the addressing
      modes need to be switched and that the noexec protection only works
      for user space.
      After switching the addressing modes, we cannot use the mvcp/mvcs
      instructions anymore to copy between kernel and user space. A new
      mvcos instruction has been added to the z9 EC/BC hardware which allows
      to copy between arbitrary address spaces, but on older hardware the
      page tables need to be walked manually.
      Signed-off-by: NGerald Schaefer <geraldsc@de.ibm.com>
      Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
      c1821c2e
  3. 12 1月, 2007 1 次提交
  4. 08 12月, 2006 1 次提交
    • H
      [S390] Virtual memmap for s390. · f4eb07c1
      Heiko Carstens 提交于
      Virtual memmap support for s390. Inspired by the ia64 implementation.
      
      Unlike ia64 we need a mechanism which allows us to dynamically attach
      shared memory regions.
      These memory regions are accessed via the dcss device driver. dcss
      implements the 'direct_access' operation, which requires struct pages
      for every single shared page.
      Therefore this implementation provides an interface to attach/detach
      shared memory:
      
      int add_shared_memory(unsigned long start, unsigned long size);
      int remove_shared_memory(unsigned long start, unsigned long size);
      
      The purpose of the add_shared_memory function is to add the given
      memory range to the 1:1 mapping and to make sure that the
      corresponding range in the vmemmap is backed with physical pages.
      It also initialises the new struct pages.
      
      remove_shared_memory in turn only invalidates the page table
      entries in the 1:1 mapping. The page tables and the memory used for
      struct pages in the vmemmap are currently not freed. They will be
      reused when the next segment will be attached.
      Given that the maximum size of a shared memory region is 2GB and
      in addition all regions must reside below 2GB this is not too much of
      a restriction, but there is room for improvement.
      Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
      Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
      f4eb07c1