1. 24 Jul, 2018 1 commit
    • Ram Pai's avatar
      powerpc/pkeys: Give all threads control of their key permissions · a57a04c7
      Ram Pai authored
      Currently in a multithreaded application, a key allocated by one
      thread is not usable by other threads. By "not usable" we mean that
      other threads are unable to change the access permissions for that
      key for themselves.
      
      When a new key is allocated in one thread, the corresponding UAMOR
      bits for that thread get enabled, however the UAMOR bits for that key
      for all other threads remain disabled.
      
      Other threads have no way to set permissions on the key, and the
      current default permissions are that read/write is enabled for all
      keys, which means the key has no effect for other threads. Although
      that may be the desired behaviour in some circumstances, having all
      threads able to control their permissions for the key is more
      flexible.
      
      The current behaviour also differs from the x86 behaviour, which is
      problematic for users.
      
      To fix this, enable the UAMOR bits for all keys, at process
      creation (in start_thread(), ie exec time). Since the contents of
      UAMOR are inherited at fork, all threads are capable of modifying the
      permissions on any key.
      
      This is technically an ABI break on powerpc, but pkey support is fairly
      new on powerpc and not widely used, and this brings us into
      line with x86.
      
      Fixes: cf43d3b2 ("powerpc: Enable pkey subsystem")
      Cc: stable@vger.kernel.org # v4.16+
      Tested-by: default avatarFlorian Weimer <fweimer@redhat.com>
      Signed-off-by: default avatarRam Pai <linuxram@us.ibm.com>
      [mpe: Reword some of the changelog]
      Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
      a57a04c7
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