From: Daniel Axtens <dja@xxxxxxxxxx> Subject: fork: support VMAP_STACK with KASAN_VMALLOC 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 Link: http://lkml.kernel.org/r/20191031093909.9228-4-dja@xxxxxxxxxx Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Christophe Leroy <christophe.leroy@xxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/Kconfig | 9 +++++---- kernel/fork.c | 4 ++++ 2 files changed, 9 insertions(+), 4 deletions(-) --- a/arch/Kconfig~fork-support-vmap_stack-with-kasan_vmalloc +++ a/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 --- a/kernel/fork.c~fork-support-vmap_stack-with-kasan_vmalloc +++ a/kernel/fork.c @@ -93,6 +93,7 @@ #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> @@ -223,6 +224,9 @@ static unsigned long *alloc_thread_stack 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); _
