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Message-ID: <6efb0e40-a1e8-45d8-8b59-c3e5a90daa4a@redhat.com>
Date: Wed, 24 Jan 2024 16:12:33 +0100
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Reply-To: eric.auger@redhat.com
Subject: Re: [PATCH 57/82] KVM: arm64: vgic-v3: Refactor intentional
 wrap-around test
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To: Kees Cook <keescook@chromium.org>, linux-hardening@vger.kernel.org
Cc: Marc Zyngier <maz@kernel.org>, Oliver Upton <oliver.upton@linux.dev>,
 James Morse <james.morse@arm.com>, Suzuki K Poulose
 <suzuki.poulose@arm.com>, Zenghui Yu <yuzenghui@huawei.com>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
 "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>
 <20240123002814.1396804-57-keescook@chromium.org>
From: Eric Auger <eric.auger@redhat.com>
In-Reply-To: <20240123002814.1396804-57-keescook@chromium.org>
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On 1/23/24 01:27, 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: Marc Zyngier <maz@kernel.org>
> Cc: Oliver Upton <oliver.upton@linux.dev>
> Cc: James Morse <james.morse@arm.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Zenghui Yu <yuzenghui@huawei.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: kvmarm@lists.linux.dev
> Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric
> ---
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> index c15ee1df036a..860b774c0c13 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> @@ -863,7 +863,7 @@ static int vgic_v3_alloc_redist_region(struct kvm *kvm, uint32_t index,
>  	int ret;
>  
>  	/* cross the end of memory ? */
> -	if (base + size < base)
> +	if (add_would_overflow(base, size))
>  		return -EINVAL;
>  
>  	if (list_empty(rd_regions)) {