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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q13sm5784525pjq.10.2021.08.18.10.48.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Aug 2021 10:48:58 -0700 (PDT) From: Kees Cook To: Greg Kroah-Hartman Cc: Kees Cook , Arnd Bergmann , Guillaume Tucker , linux-kernel@vger.kernel.org, kernelci@groups.io, linux-kselftest@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH 4/4] lkdtm/heap: Avoid __alloc_size hint warning for VMALLOC_LINEAR_OVERFLOW Date: Wed, 18 Aug 2021 10:48:55 -0700 Message-Id: <20210818174855.2307828-5-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210818174855.2307828-1-keescook@chromium.org> References: <20210818174855.2307828-1-keescook@chromium.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1433; h=from:subject; bh=hEHwsjZSD/SYU1VoaQ5mTXOJ9xQG9V/0cWsn/qe6UfM=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBhHUgGBUS/d6eL8MtIKgEouR7CqPpSrnry2WnQbOoB MJRkKMuJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYR1IBgAKCRCJcvTf3G3AJq2QEA CYtjA8ExIWPk7JvqRI/61/kE99RMnZcDBn7KzqjP0m7JW5yqwlWBUMIz+ye1hV21EL2F5arOPH8BvR 3V9TjF+7swg9wtnWeIWdkurG6SE0wnSv9XECt+FpJzNKxsa9TsUw9OzP94iXOX0lhLJtiS5hbbDzvm 1xWlOJh9WnUVQVNHoQ0SWthtBbKyUGXh/xmr3ASedX9L6Ue100evlIwHgSaY4HK18yKW2oxesg9vRq 2nfod7QFT4T2wsrMrNBcPKnaillIzxm4xYIHVZ64iXPKFsSoxJAppeZ25QJS8u431AEsh7QC1vzUHN mYYvmqS5lBlfI4JWTTS2kh/l+646Yw6u2XmBhYm/auAnyQo6Y7uDXi4YZ0qxInN+fMocEm6/SG2Ts0 q+eQTj7eahrc7dPrq34ZqReM3Anssp+dl3jbBZ4qlHzyoL8i4QUkwHKBalsUDUu0AXanwZvIuUpVRE Xspwci5AKkP3cZFW92NW3seSikRnhZFP+SnAUf9FouV5pMfGgDfGEtAe+KcNGwOiaWjjArhEqeIHzt fiQFAZHI6CJUhJ+OdyXbeFfQfR/d0PG0GUn67vyUiVMF6oqs24HnZ7vRHm5paxs7yDRBfvhx+RD1sk 77kNe3nsroN6hhYbzbAgtAbYjR89fEwFvL1eLnnR4NI6p2wq7155My+YT1IA== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Once __alloc_size hints have been added, the compiler will (correctly!) see this as an overflow. We are, however, trying to test for this condition at run-time (not compile-time), so work around it with a volatile int offset. Cc: Arnd Bergmann Signed-off-by: Kees Cook --- drivers/misc/lkdtm/heap.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c index 3d9aae5821a0..8a92f5a800fa 100644 --- a/drivers/misc/lkdtm/heap.c +++ b/drivers/misc/lkdtm/heap.c @@ -12,6 +12,13 @@ static struct kmem_cache *double_free_cache; static struct kmem_cache *a_cache; static struct kmem_cache *b_cache; +/* + * Using volatile here means the compiler cannot ever make assumptions + * about this value. This means compile-time length checks involving + * this variable cannot be performed; only run-time checks. + */ +static volatile int __offset = 1; + /* * If there aren't guard pages, it's likely that a consecutive allocation will * let us overflow into the second allocation without overwriting something real. @@ -24,7 +31,7 @@ void lkdtm_VMALLOC_LINEAR_OVERFLOW(void) two = vzalloc(PAGE_SIZE); pr_info("Attempting vmalloc linear overflow ...\n"); - memset(one, 0xAA, PAGE_SIZE + 1); + memset(one, 0xAA, PAGE_SIZE + __offset); vfree(two); vfree(one); -- 2.30.2