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Message-Id: <79532ad7be1a40637e6646eb0ada6195974df503.1537383101.git.andreyknvl@google.com>
Date: Wed, 19 Sep 2018 20:54:47 +0200
From: Andrey Konovalov <andreyknvl@...gle.com>
To: Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Christoph Lameter <cl@...ux.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mark Rutland <mark.rutland@....com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Marc Zyngier <marc.zyngier@....com>,
Dave Martin <dave.martin@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Ingo Molnar <mingo@...nel.org>,
Paul Lawrence <paullawrence@...gle.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Arnd Bergmann <arnd@...db.de>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kate Stewart <kstewart@...uxfoundation.org>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
kasan-dev@...glegroups.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-sparse@...r.kernel.org, linux-mm@...ck.org,
linux-kbuild@...r.kernel.org
Cc: Kostya Serebryany <kcc@...gle.com>,
Evgeniy Stepanov <eugenis@...gle.com>,
Lee Smith <Lee.Smith@....com>,
Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
Jacob Bramley <Jacob.Bramley@....com>,
Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
Jann Horn <jannh@...gle.com>,
Mark Brand <markbrand@...gle.com>,
Chintan Pandya <cpandya@...eaurora.org>,
Vishwath Mohan <vishwath@...gle.com>,
Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v8 08/20] kasan: add tag related helper functions
This commit adds a few helper functions, that are meant to be used to
work with tags embedded in the top byte of kernel pointers: to set, to
get or to reset (set to 0xff) the top byte.
Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
arch/arm64/mm/kasan_init.c | 2 ++
include/linux/kasan.h | 13 +++++++++
mm/kasan/kasan.h | 55 ++++++++++++++++++++++++++++++++++++++
mm/kasan/tags.c | 37 +++++++++++++++++++++++++
4 files changed, 107 insertions(+)
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 7a31e8ccbad2..ecd3f25cc323 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -250,6 +250,8 @@ void __init kasan_init(void)
memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
+ kasan_init_tags();
+
/* At this point kasan is fully initialized. Enable error messages */
init_task.kasan_depth = 0;
pr_info("KernelAddressSanitizer initialized\n");
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index e7162ca9d66b..7e5be87a05b3 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -169,6 +169,19 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
#define KASAN_SHADOW_INIT 0xFF
+void kasan_init_tags(void);
+
+void *kasan_reset_tag(const void *addr);
+
+#else /* CONFIG_KASAN_SW_TAGS */
+
+static inline void kasan_init_tags(void) { }
+
+static inline void *kasan_reset_tag(const void *addr)
+{
+ return (void *)addr;
+}
+
#endif /* CONFIG_KASAN_SW_TAGS */
#endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 19b950eaccff..63ab9775275b 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -8,6 +8,10 @@
#define KASAN_SHADOW_SCALE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
#define KASAN_SHADOW_MASK (KASAN_SHADOW_SCALE_SIZE - 1)
+#define KASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
+#define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
+#define KASAN_TAG_MAX 0xFD /* maximum value for random tags */
+
#define KASAN_FREE_PAGE 0xFF /* page was freed */
#define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */
#define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */
@@ -126,6 +130,57 @@ static inline void quarantine_reduce(void) { }
static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
#endif
+#ifdef CONFIG_KASAN_SW_TAGS
+
+#define KASAN_TAG_SHIFT 56
+#define KASAN_TAG_MASK (0xFFUL << KASAN_TAG_SHIFT)
+
+u8 random_tag(void);
+
+static inline void *set_tag(const void *addr, u8 tag)
+{
+ u64 a = (u64)addr;
+
+ a &= ~KASAN_TAG_MASK;
+ a |= ((u64)tag << KASAN_TAG_SHIFT);
+
+ return (void *)a;
+}
+
+static inline u8 get_tag(const void *addr)
+{
+ return (u8)((u64)addr >> KASAN_TAG_SHIFT);
+}
+
+static inline void *reset_tag(const void *addr)
+{
+ return set_tag(addr, KASAN_TAG_KERNEL);
+}
+
+#else /* CONFIG_KASAN_SW_TAGS */
+
+static inline u8 random_tag(void)
+{
+ return 0;
+}
+
+static inline void *set_tag(const void *addr, u8 tag)
+{
+ return (void *)addr;
+}
+
+static inline u8 get_tag(const void *addr)
+{
+ return 0;
+}
+
+static inline void *reset_tag(const void *addr)
+{
+ return (void *)addr;
+}
+
+#endif /* CONFIG_KASAN_SW_TAGS */
+
/*
* Exported functions for interfaces called from assembly or from generated
* code. Declarations here to avoid warning about missing declarations.
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 04194923c543..700323946867 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -38,6 +38,43 @@
#include "kasan.h"
#include "../slab.h"
+static DEFINE_PER_CPU(u32, prng_state);
+
+void kasan_init_tags(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(prng_state, cpu) = get_random_u32();
+}
+
+/*
+ * If a preemption happens between this_cpu_read and this_cpu_write, the only
+ * side effect is that we'll give a few allocated in different contexts objects
+ * the same tag. Since tag-based KASAN is meant to be used a probabilistic
+ * bug-detection debug feature, this doesn’t have significant negative impact.
+ *
+ * Ideally the tags use strong randomness to prevent any attempts to predict
+ * them during explicit exploit attempts. But strong randomness is expensive,
+ * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
+ * sequence has in fact positive effect, since interrupts that randomly skew
+ * PRNG at unpredictable points do only good.
+ */
+u8 random_tag(void)
+{
+ u32 state = this_cpu_read(prng_state);
+
+ state = 1664525 * state + 1013904223;
+ this_cpu_write(prng_state, state);
+
+ return (u8)(state % (KASAN_TAG_MAX + 1));
+}
+
+void *kasan_reset_tag(const void *addr)
+{
+ return reset_tag(addr);
+}
+
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip)
{
--
2.19.0.397.gdd90340f6a-goog
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