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Subject[PATCHv3] lib/test_kasan: add roundtrip tests
Date
In several places we need to be able to operate on pointers which have
gone via a roundtrip:

virt -> {phys,page} -> virt

With KASAN_SW_TAGS, we can't preserve the tag for SLUB objects, and the
{phys,page} -> virt conversion will use KASAN_TAG_KERNEL.

This patch adds tests to ensure that this works as expected, without
false positives which have recently been spotted [1,2] in testing.

[1] https://lore.kernel.org/linux-arm-kernel/20190819114420.2535-1-walter-zh.wu@mediatek.com/
[2] https://lore.kernel.org/linux-arm-kernel/20190819132347.GB9927@lakrids.cambridge.arm.com/

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Will Deacon <will.deacon@arm.com>
---
lib/test_kasan.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

Since v1:
* Spin as a separate patch
* Fix typo
* Note examples in commit message
Since v2:
* Fold Andrey Ryabinin's ack
* Include <asm/io.h> for virt_to_phys() and phys_to_virt()

Mark.

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index b63b367a94e8..91a2ec4b87f9 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -19,6 +19,9 @@
#include <linux/string.h>
#include <linux/uaccess.h>

+#include <asm/io.h>
+#include <asm/page.h>
+
/*
* Note: test functions are marked noinline so that their names appear in
* reports.
@@ -337,6 +340,42 @@ static noinline void __init kmalloc_uaf2(void)
kfree(ptr2);
}

+static noinline void __init kfree_via_page(void)
+{
+ char *ptr;
+ size_t size = 8;
+ struct page *page;
+ unsigned long offset;
+
+ pr_info("invalid-free false positive (via page)\n");
+ ptr = kmalloc(size, GFP_KERNEL);
+ if (!ptr) {
+ pr_err("Allocation failed\n");
+ return;
+ }
+
+ page = virt_to_page(ptr);
+ offset = offset_in_page(ptr);
+ kfree(page_address(page) + offset);
+}
+
+static noinline void __init kfree_via_phys(void)
+{
+ char *ptr;
+ size_t size = 8;
+ phys_addr_t phys;
+
+ pr_info("invalid-free false positive (via phys)\n");
+ ptr = kmalloc(size, GFP_KERNEL);
+ if (!ptr) {
+ pr_err("Allocation failed\n");
+ return;
+ }
+
+ phys = virt_to_phys(ptr);
+ kfree(phys_to_virt(phys));
+}
+
static noinline void __init kmem_cache_oob(void)
{
char *p;
@@ -737,6 +776,8 @@ static int __init kmalloc_tests_init(void)
kmalloc_uaf();
kmalloc_uaf_memset();
kmalloc_uaf2();
+ kfree_via_page();
+ kfree_via_phys();
kmem_cache_oob();
memcg_accounted_kmem_cache();
kasan_stack_oob();
--
2.11.0
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