Re: [PATCH v2] KVM: arm64: Fix buffer overflow in kvm_arm_set_fw_reg()

From: Marc Zyngier <maz@kernel.org>
To: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Andre Przywara <andre.przywara@arm.com>,
	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>, Eric Auger <eric.auger@redhat.com>,
	Steven Price <steven.price@arm.com>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	kernel-janitors@vger.kernel.org
Subject: Re: [PATCH v2] KVM: arm64: Fix buffer overflow in kvm_arm_set_fw_reg()
Date: Wed, 19 Apr 2023 12:31:53 +0100	[thread overview]
Message-ID: <861qkgkt06.wl-maz@kernel.org> (raw)
In-Reply-To: <4efbab8c-640f-43b2-8ac6-6d68e08280fe@kili.mountain>

Hi Dan,

On Wed, 19 Apr 2023 11:16:13 +0100,
Dan Carpenter <dan.carpenter@linaro.org> wrote:
> 
> The KVM_REG_SIZE() comes from the ioctl and it can be a power of two
> between 0-32768 but if it is more than sizeof(long) this will corrupt
> memory.
> 
> Fixes: 99adb567632b ("KVM: arm/arm64: Add save/restore support for firmware workaround state")
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> ---
> v2: The original patch was okay but checking for != sizeof(val) is
>     stricter and more Obviously Correct[tm].  Return -ENOENT instead of
>     -EINVAL in case future ioctls are added which take a different size.
> 
>  arch/arm64/kvm/hypercalls.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> index 2e16fc7b31bf..7fb4df0456de 100644
> --- a/arch/arm64/kvm/hypercalls.c
> +++ b/arch/arm64/kvm/hypercalls.c
> @@ -544,6 +544,8 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  	u64 val;
>  	int wa_level;
>  
> +	if (KVM_REG_SIZE(reg->id) != sizeof(val))
> +		return -ENOENT;
>  	if (copy_from_user(&val, uaddr, KVM_REG_SIZE(reg->id)))
>  		return -EFAULT;
>  

Thanks for the fix. In the future, please Cc me on KVM/arm64 patches
(specially this particular variety of patches...).

Reviewed-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.