[OpenBIOS] [PATCH 7/7] PPC: Remove zero page mapping from MMU to enable detection of NULL pointer dereferences

Mark Cave-Ayland mark.cave-ayland at ilande.co.uk
Fri Apr 12 14:57:47 CEST 2013


Signed-off-by: Mark Cave-Ayland <mark.cave-ayland at ilande.co.uk>
---
 openbios-devel/arch/ppc/qemu/ofmem.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/openbios-devel/arch/ppc/qemu/ofmem.c b/openbios-devel/arch/ppc/qemu/ofmem.c
index 0161a17..20e9a1a 100644
--- a/openbios-devel/arch/ppc/qemu/ofmem.c
+++ b/openbios-devel/arch/ppc/qemu/ofmem.c
@@ -549,9 +549,14 @@ ofmem_init(void)
 {
     ofmem_t *ofmem = ofmem_arch_get_private();
 
-    ofmem_claim_phys(0, get_ram_bottom(), 0);
-    ofmem_claim_virt(0, get_ram_bottom(), 0);
-    ofmem_map(0, 0, get_ram_bottom(), 0);
+    /* Map the memory (don't map page 0 to allow catching of NULL dereferences) */
+    ofmem_claim_phys(PAGE_SIZE, get_ram_bottom() - PAGE_SIZE, 0);
+    ofmem_claim_virt(PAGE_SIZE, get_ram_bottom() - PAGE_SIZE, 0);
+    ofmem_map(PAGE_SIZE, PAGE_SIZE, get_ram_bottom() - PAGE_SIZE, 0);
+
+    /* Mark the first page as non-free */
+    ofmem_claim_phys(0, PAGE_SIZE, 0);
+    ofmem_claim_virt(0, PAGE_SIZE, 0);
 
     /* Map everything at the top of physical RAM 1:1, minus the OpenBIOS ROM in RAM copy */
     ofmem_claim_phys(get_ram_top(), get_hash_base() + HASH_SIZE - get_ram_top(), 0);
-- 
1.7.10.4




More information about the OpenBIOS mailing list