powerpc/mm/radix: Only add X for pages overlapping kernel text
authorMichael Ellerman <mpe@ellerman.id.au>
Tue, 6 Jun 2017 05:48:57 +0000 (15:48 +1000)
committerMichael Ellerman <mpe@ellerman.id.au>
Thu, 15 Jun 2017 06:34:39 +0000 (16:34 +1000)
commit9abcc981de9775659a0f6e4a52a3448ea72e59da
tree203f821fb6d73a41dfd97c8fca401a5615a4597f
parent0edc2ca9ccc9df99f7a94b6407ae2a0ff27d86b2
powerpc/mm/radix: Only add X for pages overlapping kernel text

Currently we map the whole linear mapping with PAGE_KERNEL_X. Instead we
should check if the page overlaps the kernel text and only then add
PAGE_KERNEL_X.

Note that we still use 1G pages if they're available, so this will
typically still result in a 1G executable page at KERNELBASE. So this fix is
primarily useful for catching stray branches to high linear mapping addresses.

Without this patch, we can execute at 1G in xmon using:

  0:mon> m c000000040000000
  c000000040000000  00 l
  c000000040000000  00000000 01006038
  c000000040000004  00000000 2000804e
  c000000040000008  00000000 x
  0:mon> di c000000040000000
  c000000040000000  38600001      li      r3,1
  c000000040000004  4e800020      blr
  0:mon> p c000000040000000
  return value is 0x1

After we get a 400 as expected:

  0:mon> p c000000040000000
  *** 400 exception occurred

Fixes: 2bfd65e45e87 ("powerpc/mm/radix: Add radix callbacks for early init routines")
Cc: stable@vger.kernel.org # v4.7+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Balbir Singh <bsingharora@gmail.com>
arch/powerpc/mm/pgtable-radix.c