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From: Daniel Axtens <dja@axtens.net>
To: kasan-dev@googlegroups.com, linux-mm@kvack.org, x86@kernel.org,
	aryabinin@virtuozzo.com, glider@google.com, luto@kernel.org,
	linux-kernel@vger.kernel.org, mark.rutland@arm.com,
	dvyukov@google.com, christophe.leroy@c-s.fr
Cc: linuxppc-dev@lists.ozlabs.org, gor@linux.ibm.com,
	Daniel Axtens <dja@axtens.net>
Subject: [PATCH v9 3/5] fork: support VMAP_STACK with KASAN_VMALLOC
Date: Thu, 17 Oct 2019 12:25:04 +1100	[thread overview]
Message-ID: <20191017012506.28503-4-dja@axtens.net> (raw)
In-Reply-To: <20191017012506.28503-1-dja@axtens.net>

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(-)

diff --git arch/Kconfig arch/Kconfig
index 5f8a5d84dbbe..2d914990402f 100644
--- arch/Kconfig
+++ 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 kernel/fork.c kernel/fork.c
index bcdf53125210..484ca6b0ae6c 100644
--- kernel/fork.c
+++ 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);
 
-- 
2.20.1



  parent reply	other threads:[~2019-10-17  1:25 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-17  1:25 [PATCH v9 0/5] kasan: support backing vmalloc space with real shadow memory Daniel Axtens
2019-10-17  1:25 ` [PATCH v9 1/5] " Daniel Axtens
2019-10-17  1:25 ` [PATCH v9 2/5] kasan: add test for vmalloc Daniel Axtens
2019-10-17  1:25 ` Daniel Axtens [this message]
2019-10-17  1:25 ` [PATCH v9 4/5] x86/kasan: support KASAN_VMALLOC Daniel Axtens
2019-10-17  1:25 ` [PATCH v9 5/5] kasan debug: track pages allocated for vmalloc shadow Daniel Axtens

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