linux-hardening - [PATCH] kasan: test: Consolidate workarounds for unwanted __alloc

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Date:   Wed, 20 Oct 2021 12:38:07 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] kasan: test: Consolidate workarounds for unwanted __alloc_size() protection

This fixes kasan-test-use-underlying-string-helpers.patch to avoid needing
new helpers. As done in kasan-test-bypass-__alloc_size-checks.patch,
just use OPTIMIZER_HIDE_VAR(). Additionally converts a use of
"volatile", which was trying to work around similar detection.

Cc: Arnd Bergmann <arnd@...db.de>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Andrey Konovalov <andreyknvl@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: kasan-dev@...glegroups.com
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Hi Andrew,

Can you please collapse this into your series? It's cleaner to use the
same method everywhere in this file to avoid the compiler being smart. :)

Thanks!

-Kees
---
 lib/test_kasan.c | 24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 318fc612e7e7..96a1f085b460 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -525,12 +525,13 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
 {
 	char *ptr;
 	size_t size = 64;
-	volatile size_t invalid_size = size;
+	size_t invalid_size = size;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	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);
@@ -852,21 +853,6 @@ static void kmem_cache_invalid_free(struct kunit *test)
 	kmem_cache_destroy(cache);
 }
 
-/*
- * noinline wrappers to prevent the compiler from noticing the overflow
- * at compile time rather than having kasan catch it.
- */
-static noinline void *__kasan_memchr(const void *s, int c, size_t n)
-{
-	return memchr(s, c, n);
-}
-
-static noinline int __kasan_memcmp(const void *s1, const void *s2, size_t n)
-{
-	return memcmp(s1, s2, n);
-}
-
-
 static void kasan_memchr(struct kunit *test)
 {
 	char *ptr;
@@ -884,8 +870,9 @@ static void kasan_memchr(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
-		kasan_ptr_result = __kasan_memchr(ptr, '1', size + 1));
+		kasan_ptr_result = memchr(ptr, '1', size + 1));
 
 	kfree(ptr);
 }
@@ -909,8 +896,9 @@ static void kasan_memcmp(struct kunit *test)
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 	memset(arr, 0, sizeof(arr));
 
+	OPTIMIZER_HIDE_VAR(size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
-		kasan_int_result = __kasan_memcmp(ptr, arr, size+1));
+		kasan_int_result = memcmp(ptr, arr, size+1));
 	kfree(ptr);
 }
 
-- 
2.30.2