linux-kernel - Re: [PATCH] refcount: Annotated intentional signed integer wrap-around

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Message-ID: <CANiq72mab-U9i0qVre7yucfi2oRHJ2yQPDju4sQuTb6HjCy7WQ@mail.gmail.com>
Date: Wed, 21 Feb 2024 11:30:33 +0100
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Will Deacon <will@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>, 
	Mark Rutland <mark.rutland@....com>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] refcount: Annotated intentional signed integer wrap-around

On Wed, Feb 21, 2024 at 6:16 AM Kees Cook <keescook@...omium.org> wrote:
>
> Mark the various refcount_t functions with __signed_wrap, as we depend
> on the wrapping behavior to detect the overflow and perform saturation.
> Silences warnings seen with the LKDTM REFCOUNT_* tests:
>
>   UBSAN: signed-integer-overflow in ../include/linux/refcount.h:189:11
>   2147483647 + 1 cannot be represented in type 'int'
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Not sure why I am the "To:" (i.e. even if it is a change involving
only an addition of an attribute), but it looks good to me (UBSan is
triggering on the few `old + i`s caused by the calls from
`drivers/misc/lkdtm/refcount.c`, right?):

Reviewed-by: Miguel Ojeda <ojeda@...nel.org>

As usual, thanks Kees for keeping up on getting the kernel (un)signed
UBSan-clean :)

Cheers,
Miguel