On 15/11/16 21:57, Michael Ellerman wrote: > POISON_POINTER_DELTA is defined in poison.h, and is intended to be used > to shift poison values so that they don't alias userspace. > > We should add it to ZERO_SIZE_PTR so that attackers can't use > ZERO_SIZE_PTR as a way to get a pointer to userspace. > > Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > --- > include/linux/slab.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 084b12bad198..17ddd7aea2dd 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -12,6 +12,7 @@ > #define _LINUX_SLAB_H > > #include <linux/gfp.h> > +#include <linux/poison.h> > #include <linux/types.h> > #include <linux/workqueue.h> > > @@ -109,7 +110,7 @@ > * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can. > * Both make kfree a no-op. > */ > -#define ZERO_SIZE_PTR ((void *)16) > +#define ZERO_SIZE_PTR ((void *)(16 + POISON_POINTER_DELTA)) > > #define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \ > (unsigned long)ZERO_SIZE_PTR) > I wonder if we should make this a variable with boot time entropy within a certain region Balbir Singh. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>