Commit 08ae6cc1 authored by Paul Mackerras's avatar Paul Mackerras
Browse files

[POWERPC] Allow exec faults on readable areas on classic 32-bit PowerPC

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

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: default avatarPaul Mackerras <>
Acked-by: default avatarJon Loeliger <>
parent ca8ffc97
...@@ -283,7 +283,13 @@ good_area: ...@@ -283,7 +283,13 @@ good_area:
/* protection fault */ /* protection fault */
if (error_code & DSISR_PROTFAULT) if (error_code & DSISR_PROTFAULT)
goto bad_area; goto bad_area;
if (!(vma->vm_flags & VM_EXEC)) /*
* Allow execution from readable areas if the MMU does not
* provide separate controls over reading and executing.
if (!(vma->vm_flags & VM_EXEC) &&
(cpu_has_feature(CPU_FTR_NOEXECUTE) ||
!(vma->vm_flags & (VM_READ | VM_WRITE))))
goto bad_area; goto bad_area;
#else #else
pte_t *ptep; pte_t *ptep;
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