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Subject[PATCH 4.12 049/196] powerpc/mm/radix: Only add X for pages overlapping kernel text
Date
4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Ellerman <mpe@ellerman.id.au>

commit 9abcc981de9775659a0f6e4a52a3448ea72e59da upstream.

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")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/mm/pgtable-radix.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -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_mappi
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_map
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;
}

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