| Message ID | 20191029042059.28541-4-dja@axtens.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kasan: support backing vmalloc space with real shadow memory | expand |
On 10/29/19 7:20 AM, Daniel Axtens wrote: > Supporting VMAP_STACK with KASAN_VMALLOC is straightforward: > > - clear the shadow region of vmapped stacks when swapping them in > - tweak Kconfig to allow VMAP_STACK to be turned on with KASAN > > Reviewed-by: Dmitry Vyukov <dvyukov@google.com> > Signed-off-by: Daniel Axtens <dja@axtens.net> > --- Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > > diff --git a/kernel/fork.c b/kernel/fork.c > index 954e875e72b1..a6e5249ad74b 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -94,6 +94,7 @@ > #include <linux/livepatch.h> > #include <linux/thread_info.h> > #include <linux/stackleak.h> > +#include <linux/kasan.h> > > #include <asm/pgtable.h> > #include <asm/pgalloc.h> > @@ -224,6 +225,9 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) > if (!s) > continue; > > + /* Clear the KASAN shadow of the stack. */ > + kasan_unpoison_shadow(s->addr, THREAD_SIZE); > + Just sharing the thought. We could possibly add poisoning in free_thread_stack() to catch possible usage of freed cached stack. But it might be a bad idea because cached stacks supposed to be reused very quickly. So it might just add overhead without much gain. > /* Clear stale pointers from reused stack. */ > memset(s->addr, 0, THREAD_SIZE); > >
diff --git a/arch/Kconfig b/arch/Kconfig index 5f8a5d84dbbe..2d914990402f 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -843,16 +843,17 @@ config HAVE_ARCH_VMAP_STACK config VMAP_STACK default y bool "Use a virtually-mapped stack" - depends on HAVE_ARCH_VMAP_STACK && !KASAN + depends on HAVE_ARCH_VMAP_STACK + depends on !KASAN || KASAN_VMALLOC ---help--- Enable this if you want the use virtually-mapped kernel stacks with guard pages. This causes kernel stack overflows to be caught immediately rather than causing difficult-to-diagnose corruption. - This is presently incompatible with KASAN because KASAN expects - the stack to map directly to the KASAN shadow map using a formula - that is incorrect if the stack is in vmalloc space. + To use this with KASAN, the architecture must support backing + virtual mappings with real shadow memory, and KASAN_VMALLOC must + be enabled. config ARCH_OPTIONAL_KERNEL_RWX def_bool n diff --git a/kernel/fork.c b/kernel/fork.c index 954e875e72b1..a6e5249ad74b 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -94,6 +94,7 @@ #include <linux/livepatch.h> #include <linux/thread_info.h> #include <linux/stackleak.h> +#include <linux/kasan.h> #include <asm/pgtable.h> #include <asm/pgalloc.h> @@ -224,6 +225,9 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) if (!s) continue; + /* Clear the KASAN shadow of the stack. */ + kasan_unpoison_shadow(s->addr, THREAD_SIZE); + /* Clear stale pointers from reused stack. */ memset(s->addr, 0, THREAD_SIZE);