linux-hardening - [PATCH 41/82] wil6210: Refactor intentional wrap-around test

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Message-Id: <20240123002814.1396804-41-keescook@chromium.org>
Date: Mon, 22 Jan 2024 16:27:16 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-hardening@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>,
	Kalle Valo <kvalo@...nel.org>,
	Johannes Berg <johannes.berg@...el.com>,
	Max Chen <mxchen@...eaurora.org>,
	Yang Shen <shenyang39@...wei.com>,
	linux-wireless@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 41/82] wil6210: Refactor intentional wrap-around test

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Kalle Valo <kvalo@...nel.org>
Cc: Johannes Berg <johannes.berg@...el.com>
Cc: Max Chen <mxchen@...eaurora.org>
Cc: Yang Shen <shenyang39@...wei.com>
Cc: linux-wireless@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/net/wireless/ath/wil6210/wmi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/wil6210/wmi.c b/drivers/net/wireless/ath/wil6210/wmi.c
index 6fdb77d4c59e..3b3c991f77e9 100644
--- a/drivers/net/wireless/ath/wil6210/wmi.c
+++ b/drivers/net/wireless/ath/wil6210/wmi.c
@@ -286,7 +286,7 @@ void __iomem *wmi_buffer_block(struct wil6210_priv *wil, __le32 ptr_, u32 size)
 	off = HOSTADDR(ptr);
 	if (off > wil->bar_size - 4)
 		return NULL;
-	if (size && ((off + size > wil->bar_size) || (off + size < off)))
+	if (size && ((off + size > wil->bar_size) || (add_would_overflow(off, size))))
 		return NULL;

 	return wil->csr + off;
-- 
2.34.1