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

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Date: Tue, 23 Jan 2024 14:52:31 -0800
From: Kees Cook <keescook@...omium.org>
To: Kalle Valo <kvalo@...nel.org>
Cc: linux-hardening@...r.kernel.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: Re: [PATCH 41/82] wil6210: Refactor intentional wrap-around test

On Tue, Jan 23, 2024 at 11:50:34AM +0000, Kalle Valo wrote:
> Kees Cook <keescook@...omium.org> wrote:
> 
> > 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>
> > Acked-by: Kalle Valo <kvalo@...nel.org>
> 
> If you can edit before commit please add "wifi:" prefix to the wireless patches:
> 
> ERROR: 'wifi:' prefix missing: '[PATCH 41/82] wil6210: Refactor intentional wrap-around test'
> ERROR: 'wifi:' prefix missing: '[PATCH 62/82] mwifiex: pcie: Refactor intentional wrap-around test'

Ah yes, thank you! I will adjust them.

-Kees

> 
> 2 patches set to Not Applicable.
> 
> 13526631 [41/82] wil6210: Refactor intentional wrap-around test
> 13526632 [62/82] mwifiex: pcie: Refactor intentional wrap-around test
> 
> -- 
> https://patchwork.kernel.org/project/linux-wireless/patch/20240123002814.1396804-41-keescook@chromium.org/
> 
> https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
> 

-- 
Kees Cook