diff mbox series

[v10,3/5] fork: support VMAP_STACK with KASAN_VMALLOC

Message ID 20191029042059.28541-4-dja@axtens.net (mailing list archive)
State Superseded
Headers show
Series kasan: support backing vmalloc space with real shadow memory | expand

Checks

Context Check Description
snowpatch_ozlabs/apply_patch warning Failed to apply on branch powerpc/merge (a437a1c6e54c045f19f7d894b2a749bc5155f19a)
snowpatch_ozlabs/apply_patch warning Failed to apply on branch powerpc/next (612ee81b9461475b5a5612c2e8d71559dd3c7920)
snowpatch_ozlabs/apply_patch warning Failed to apply on branch linus/master (8005803a2ca0af49f36f6e9329b5ecda3df27347)
snowpatch_ozlabs/apply_patch warning Failed to apply on branch powerpc/fixes (a8a30219ba78b1abb92091102b632f8e9bbdbf03)
snowpatch_ozlabs/apply_patch success Successfully applied on branch linux-next (60c1769a45f4b6beddcc48843739d7d41b88dc1c)
snowpatch_ozlabs/checkpatch success total: 0 errors, 0 warnings, 0 checks, 37 lines checked

Commit Message

Daniel Axtens Oct. 29, 2019, 4:20 a.m. UTC 
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>
---
 arch/Kconfig  | 9 +++++----
 kernel/fork.c | 4 ++++
 2 files changed, 9 insertions(+), 4 deletions(-)

Comments

Andrey Ryabinin Oct. 29, 2019, 5:07 p.m. UTC | #1 
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 mbox series

Patch

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);