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Make PROT_WRITE imply PROT_READ for a number of architectures which don't
support write only in hardware.
While looking at this, I noticed that some architectures which do not
support write only mappings already take the exact same approach. For
example, in arch/alpha/mm/fault.c:
"
if (cause < 0) {
if (!(vma->vm_flags & VM_EXEC))
goto bad_area;
} else if (!cause) {
/* Allow reads even for write-only mappings */
if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
goto bad_area;
} else {
if (!(vma->vm_flags & VM_WRITE))
goto bad_area;
}
"
Thus, this patch brings other architectures which do not support write only
mappings in-line and consistent with the rest. I've verified the patch on
ia64, x86_64 and x86.
Additional discussion:
Several architectures, including x86, can not support write-only mappings.
The pte for x86 reserves a single bit for protection and its two states are
read only or read/write. Thus, write only is not supported in h/w.
Currently, if i 'mmap' a page write-only, the first read attempt on that page
creates a page fault and will SEGV. That check is enforced in
arch/blah/mm/fault.c. However, if i first write that page it will fault in
and the pte will be set to read/write. Thus, any subsequent reads to the page
will succeed. It is this inconsistency in behavior that this patch is
attempting to address. Furthermore, if the page is swapped out, and then
brought back the first read will also cause a SEGV. Thus, any arbitrary read
on a page can potentially result in a SEGV.
According to the SuSv3 spec, "if the application requests only PROT_WRITE, the
implementation may also allow read access." Also as mentioned, some
archtectures, such as alpha, shown above already take the approach that i am
suggesting.
The counter-argument to this raised by Arjan, is that the kernel is enforcing
the write only mapping the best it can given the h/w limitations. This is
true, however Alan Cox, and myself would argue that the inconsitency in
behavior, that is applications can sometimes work/sometimes fails is highly
undesireable. If you read through the thread, i think people, came to an
agreement on the last patch i posted, as nobody has objected to it...
Signed-off-by: Jason Baron <[email protected]>
Cc: Russell King <[email protected]>
Cc: "Luck, Tony" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Roman Zippel <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Acked-by: Andi Kleen <[email protected]>
Acked-by: Alan Cox <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Acked-by: Paul Mundt <[email protected]>
Cc: Kazumoto Kojima <[email protected]>
Cc: Ian Molton <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Signed-off-by: Jörn Engel <[email protected]>
Signed-off-by: Adrian Bunk <[email protected]>
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Overloading of page fault notification with the notify_die() has performance
issues(since the only interested components for page fault is kprobes and/or
kdb) and hence this patch introduces the new notifier call chain exclusively
for page fault notifications their by avoiding notifying unnecessary
components in the do_page_fault() code path.
Signed-off-by: Anil S Keshavamurthy <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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This comment exceeded my bad spelling threshold :)
Signed-off-by: Anton Blanchard <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
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Fix 44x and BookE page fault handler to correctly lock PTE before
trying to pte_update() it, otherwise this PTE might be swapped out
after pte_present() check but before pte_uptdate() call, resulting in
corrupted PTE. This can happen with enabled preemption and low memory
condition.
Signed-off-by: Eugene Surovegin <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
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This patch removes all self references and fixes references to files
in the now defunct arch/ppc64 tree. I think this accomplises
everything wanted, though there might be a few references I missed.
Signed-off-by: Jon Mason <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
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When taking a DABR exception we were reporting the PC. It makes more
sense to report the address that caused the exception, and the gdb guys
would like it that way.
Signed-off-by: Anton Blanchard <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
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Add nicer printing of faulting address on unresolvable kernel faults.
Makes life a little easier for those who don't know how to decode our
register contents at oops time.
Signed-off-by: Olof Johansson <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
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do_dabr() is not relevant on 40x or Book-E processors so dont build it
Signed-off-by: Kumar K. Gala <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
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This creates the directory structure under arch/powerpc and a bunch
of Kconfig files. It does a first-cut merge of arch/powerpc/mm,
arch/powerpc/lib and arch/powerpc/platforms/powermac. This is enough
to build a 32-bit powermac kernel with ARCH=powerpc.
For now we are getting some unmerged files from arch/ppc/kernel and
arch/ppc/syslib, or arch/ppc64/kernel. This makes some minor changes
to files in those directories and files outside arch/powerpc.
The boot directory is still not merged. That's going to be interesting.
Signed-off-by: Paul Mackerras <[email protected]>
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