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Message-ID: <5bfb2175-2470-469b-b3fa-9f14fae08536@kernel.org>
Date: Tue, 23 Jan 2024 07:15:07 -0600
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Subject: Re: [PATCH 65/82] nios2: Refactor intentional wrap-around test
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To: Kees Cook <keescook@chromium.org>, linux-hardening@vger.kernel.org
Cc: Jann Horn <jannh@google.com>, Ley Foon Tan <ley.foon.tan@intel.com>,
 "Gustavo A. R. Silva" <gustavoars@kernel.org>,
 Bill Wendling <morbo@google.com>, Justin Stitt <justinstitt@google.com>,
 linux-kernel@vger.kernel.org
References: <20240122235208.work.748-kees@kernel.org>
 <20240123002814.1396804-65-keescook@chromium.org>
From: Dinh Nguyen <dinguyen@kernel.org>
In-Reply-To: <20240123002814.1396804-65-keescook@chromium.org>
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On 1/22/24 18:27, Kees Cook 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: Dinh Nguyen <dinguyen@kernel.org>
> Cc: Jann Horn <jannh@google.com>
> Cc: Ley Foon Tan <ley.foon.tan@intel.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>   arch/nios2/kernel/sys_nios2.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 

Acked-by: Dinh Nguyen <dinguyen@kernel.org>