1. 06 Sep, 2022 1 commit
    • Ard Biesheuvel's avatar
      arm64: compat: Implement misalignment fixups for multiword loads · 3fc24ef3
      Ard Biesheuvel authored
      The 32-bit ARM kernel implements fixups on behalf of user space when
      using LDM/STM or LDRD/STRD instructions on addresses that are not 32-bit
      aligned. This is not something that is supported by the architecture,
      but was done anyway to increase compatibility with user space software,
      which mostly targeted x86 at the time and did not care about aligned
      accesses.
      
      This feature is one of the remaining impediments to being able to switch
      to 64-bit kernels on 64-bit capable hardware running 32-bit user space,
      so let's implement it for the arm64 compat layer as well.
      
      Note that the intent is to implement the exact same handling of
      misaligned multi-word loads and stores as the 32-bit kernel does,
      including what appears to be missing support for user space programs
      that rely on SETEND to switch to a different byte order and back. Also,
      like the 32-bit ARM version, we rely on the faulting address reported by
      the CPU to infer the memory address, instead of decoding the instruction
      fully to obtain this information.
      
      This implementation is taken from the 32-bit ARM tree, with all pieces
      removed that deal with instructions other than LDRD/STRD and LDM/STM, or
      that deal with alignment exceptions taken in kernel mode.
      
      Cc: debian-arm@lists.debian.org
      Cc: Vagrant Cascadian <vagrant@debian.org>
      Cc: Riku Voipio <riku.voipio@iki.fi>
      Cc: Steve McIntyre <steve@einval.com>
      Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
      Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
      Link: https://lore.kernel.org/r/20220701135322.3025321-1-ardb@kernel.org
      [catalin.marinas@arm.com: change the option to 'default n']
      Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
      3fc24ef3
  2. 28 Aug, 2022 25 commits
  3. 27 Aug, 2022 14 commits