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powerpc/mm/radix: Only add X for pages overlapping kernel text

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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: 2bfd65e45e ("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>
This commit is contained in:
Michael Ellerman 2017-06-06 15:48:57 +10:00
parent 0edc2ca9cc
commit 9abcc981de
1 changed files with 11 additions and 3 deletions
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14
arch/powerpc/mm/pgtable-radix.c
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@ -19,6 +19,7 @@
#include <asm/mmu.h>
#include <asm/firmware.h>
#include <asm/powernv.h>
#include <asm/sections.h>
#include <trace/events/thp.h>
@ -121,7 +122,8 @@ static inline void __meminit print_mapping(unsigned long start,
static int __meminit create_physical_mapping(unsigned long start,
unsigned long end)
{
unsigned long addr, mapping_size = 0;
unsigned long vaddr, addr, mapping_size = 0;
pgprot_t prot;
start = _ALIGN_UP(start, PAGE_SIZE);
for (addr = start; addr < end; addr += mapping_size) {
@ -145,8 +147,14 @@ static int __meminit create_physical_mapping(unsigned long start,
start = addr;
}
rc = radix__map_kernel_page((unsigned long)__va(addr), addr,
PAGE_KERNEL_X, mapping_size);
vaddr = (unsigned long)__va(addr);
if (overlaps_kernel_text(vaddr, vaddr + mapping_size))
prot = PAGE_KERNEL_X;
else
prot = PAGE_KERNEL;
rc = radix__map_kernel_page(vaddr, addr, prot, mapping_size);
if (rc)
return rc;
}