linux-kernel - [PATCH] kasan: test: Silence allocation warnings from GCC 12

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Date:   Sun, 13 Feb 2022 10:32:32 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        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: Silence allocation warnings from GCC 12

GCC 12 is able to see more problems with allocation sizes at compile
time, so these must be silenced so the runtime checks will still be
available. Use OPTIMIZER_HIDE_VAR() to silence the new warnings:

lib/test_kasan.c: In function 'ksize_uaf':
lib/test_kasan.c:781:61: warning: array subscript 120 is outside array bounds of 'void[120]' [-Warray-bounds]
  781 |         KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
      |                                       ~~~~~~~~~~~~~~~~~~~~~~^~~~~~
lib/test_kasan.c:96:9: note: in definition of macro 'KUNIT_EXPECT_KASAN_FAIL'
   96 |         expression;                                                     \
      |         ^~~~~~~~~~
In function 'kmalloc',
    inlined from 'ksize_uaf' at lib/test_kasan.c:775:8:
./include/linux/slab.h:581:24: note: at offset 120 into object of size 120 allocated by 'kmem_cache_alloc_trace'
  581 |                 return kmem_cache_alloc_trace(
      |                        ^~~~~~~~~~~~~~~~~~~~~~~
  582 |                                 kmalloc_caches[kmalloc_type(flags)][index],
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  583 |                                 flags, size);
      |                                 ~~~~~~~~~~~~

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>
---
 lib/test_kasan.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 26a5c9007653..a19b3d608e3e 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -124,6 +124,7 @@ static void kmalloc_oob_right(struct kunit *test)
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	OPTIMIZER_HIDE_VAR(ptr);
 
 	/*
 	 * An unaligned access past the requested kmalloc size.
@@ -185,6 +186,7 @@ static void kmalloc_pagealloc_oob_right(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(ptr);
 	KUNIT_EXPECT_KASAN_FAIL(test, ptr[size + OOB_TAG_OFF] = 0);
 
 	kfree(ptr);
@@ -265,6 +267,7 @@ static void kmalloc_large_oob_right(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(ptr);
 	KUNIT_EXPECT_KASAN_FAIL(test, ptr[size] = 0);
 	kfree(ptr);
 }
@@ -748,6 +751,7 @@ static void ksize_unpoisons_memory(struct kunit *test)
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	OPTIMIZER_HIDE_VAR(ptr);
 	real_size = ksize(ptr);
 
 	/* This access shouldn't trigger a KASAN report. */
-- 
2.30.2