[patch 031/262] kasan: test: bypass __alloc_size checks

Andrew Morton
2021-11-05T20:36:15Z

From: Kees Cook <keescook@chromium.org>
Subject: kasan: test: bypass __alloc_size checks

Intentional overflows, as performed by the KASAN tests, are detected at
compile time[1] (instead of only at run-time) with the addition of
__alloc_size. Fix this by forcing the compiler into not being able to
trust the size used following the kmalloc()s.

[1] https://lore.kernel.org/lkml/20211005184717.65c6d8eb39350395e387b71f@linux-foundation.org

Link: https://lkml.kernel.org/r/20211006181544.1670992-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

lib/test_kasan.c | 8 +++++++-
lib/test_kasan_module.c | 2 ++
2 files changed, 9 insertions(+), 1 deletion(-)

--- a/lib/test_kasan.c~kasan-test-bypass-__alloc_size-checks
+++ a/lib/test_kasan.c
@@ -440,6 +440,7 @@ static void kmalloc_oob_memset_2(struct
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

+ OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, 2));
kfree(ptr);
}
@@ -452,6 +453,7 @@ static void kmalloc_oob_memset_4(struct
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

+ OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, 4));
kfree(ptr);
}
@@ -464,6 +466,7 @@ static void kmalloc_oob_memset_8(struct
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

+ OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, 8));
kfree(ptr);
}
@@ -476,6 +479,7 @@ static void kmalloc_oob_memset_16(struct
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

+ OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, 16));
kfree(ptr);
}
@@ -488,6 +492,7 @@ static void kmalloc_oob_in_memset(struct
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

+ OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
memset(ptr, 0, size + KASAN_GRANULE_SIZE));
kfree(ptr);
@@ -497,7 +502,7 @@ static void kmalloc_memmove_negative_siz
{
char *ptr;
size_t size = 64;
- volatile size_t invalid_size = -2;
+ size_t invalid_size = -2;

/*
* Hardware tag-based mode doesn't check memmove for negative size.
@@ -510,6 +515,7 @@ static void kmalloc_memmove_negative_siz
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

memset((char *)ptr, 0, 64);
+ OPTIMIZER_HIDE_VAR(invalid_size);
KUNIT_EXPECT_KASAN_FAIL(test,
memmove((char *)ptr, (char *)ptr + 4, invalid_size));
kfree(ptr);
--- a/lib/test_kasan_module.c~kasan-test-bypass-__alloc_size-checks
+++ a/lib/test_kasan_module.c
@@ -35,6 +35,8 @@ static noinline void __init copy_user_te
return;
}

+ OPTIMIZER_HIDE_VAR(size);
+
pr_info("out-of-bounds in copy_from_user()\n");
unused = copy_from_user(kmem, usermem, size + 1);

_