* [patch 095/158] fork: support VMAP_STACK with KASAN_VMALLOC
@ 2019-12-01 1:54 akpm
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From: akpm @ 2019-12-01 1:54 UTC (permalink / raw)
To: akpm, aryabinin, christophe.leroy, dja, dvyukov, glider, gor,
linux-mm, mark.rutland, mm-commits, torvalds
From: Daniel Axtens <dja@axtens.net>
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@axtens.net
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
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);
_
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