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    [POWERPC] Allow exec faults on readable areas on classic 32-bit PowerPC · 08ae6cc1
    Paul Mackerras 提交于
    Classic 32-bit PowerPC CPUs, and the early 64-bit PowerPC CPUs, don't
    provide a way to prevent execution from readable pages, that is, the
    MMU doesn't distinguish between data reads and instruction reads,
    although a different exception is taken for faults in data accesses
    and instruction accesses.
    
    Commit 9ba4ace3, in the course of
    fixing another bug, added a check that meant that a page fault due
    to an instruction access would fail if the vma did not have the
    VM_EXEC flag set.  This gives an inconsistent enforcement on these
    CPUs of the no-execute status of the vma (since reading from the page
    is sufficient to allow subsequent execution from it), and causes old
    versions of ppc32 glibc (2.2 and earlier) to fail, since they rely
    on executing the word before the GOT but don't have it marked
    executable.
    
    This fixes the problem by allowing execution from readable (or writable)
    areas on CPUs which do not provide separate control over data and
    instruction reads.
    Signed-off-by: NPaul Mackerras <paulus@samba.org>
    Acked-by: NJon Loeliger <jdl@freescale.com>
    08ae6cc1
fault.c 11.7 KB