NetBSD master CVS tree commits

[source%NetBSD.ORG@localhost]

thorpej
Sat Oct 19 01:51:36 PDT 1996
Update of /cvsroot/src/sys/arch/hp300/hp300
In directory netbsd1:/var/slash-tmp/cvs-serv28563

Modified Files:
        machdep.c 
Log Message:
Set up a kernel_map entry for the text segment with protection of
VM_PROT_READ|VM_PROT_EXECUTE.  The previous default (VM_PROT_ALL)
would cause the following scenario:
        - someone attempts to write kernel text (my test was writing
          to an offset of /dev/kmem which was known to be in the text
          segment, while in single-user mode).
        - enter trap() with MMU fault (because of RO pte).
        - trap() calls vm_fault(), which looks up vm_map_entry for
          fauling address.
        - vm_fault interprets write fault and VM_PROT_WRITE (in VM_PROT_ALL)
          as COW; new page allocated, data copied to new page, new page
          mapped in at trunc_page(<faulting va>).
        - wow, look at the fireworks!
Fixes two potential symptoms:
        - kernacc() returns TRUE when checking for permission to write
          an offset in kernel text, which is bogus, since the text has
          been mapped RO by pmap_bootstrap().
        - Handling of a stray pointer that attempted to scribble into
          kernel text would not be executed properly.