linux-hardening - Re: [PATCH v2] bus: mhi: ep: Use kcalloc() instead of kzalloc()

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Date: Tue, 30 Jan 2024 05:23:58 -0600
From: Alex Elder <elder@...aro.org>
To: Erick Archer <erick.archer@....com>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Jeffrey Hugo <quic_jhugo@...cinc.com>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Dan Carpenter <error27@...il.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, mhi@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] bus: mhi: ep: Use kcalloc() instead of kzalloc()

On 1/28/24 5:27 AM, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1].
> 
> Here the multiplication is obviously safe because the "event_rings"
> member never can have a value greater than 255 (8 bits). This member
> is set twice using always FIELD_GET:
> 
> mhi_cntrl->event_rings = FIELD_GET(MHICFG_NER_MASK, regval);
> mhi_cntrl->event_rings = FIELD_GET(MHICFG_NER_MASK, regval);
> 
> And the MHICFG_NER_MASK macro defines the 8 bits mask that guarantees
> a maximum value of 255.
> 
> However, using kcalloc() is more appropriate [1] and improves
> readability. This patch has no effect on runtime behavior.
> 
> Link: https://github.com/KSPP/linux/issues/162 [1]
> Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> Signed-off-by: Erick Archer <erick.archer@....com>
> ---
> Changes in v2:
> - Add more info in the commit message to better explain the change.
>    (Dan Carpenter)
> - Add the "Reviewed-by:" tag.

Looks good.

Reviewed-by: Alex Elder <elder@...aro.org>

> 
> Previous versions:
> v1 - https://lore.kernel.org/linux-hardening/20240120152518.13006-1-erick.archer@gmx.com/
> ---
>   drivers/bus/mhi/ep/main.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
> index 65fc1d738bec..8d7a4102bdb7 100644
> --- a/drivers/bus/mhi/ep/main.c
> +++ b/drivers/bus/mhi/ep/main.c
> @@ -1149,8 +1149,9 @@ int mhi_ep_power_up(struct mhi_ep_cntrl *mhi_cntrl)
>   	mhi_ep_mmio_mask_interrupts(mhi_cntrl);
>   	mhi_ep_mmio_init(mhi_cntrl);
> 
> -	mhi_cntrl->mhi_event = kzalloc(mhi_cntrl->event_rings * (sizeof(*mhi_cntrl->mhi_event)),
> -					GFP_KERNEL);
> +	mhi_cntrl->mhi_event = kcalloc(mhi_cntrl->event_rings,
> +				       sizeof(*mhi_cntrl->mhi_event),
> +				       GFP_KERNEL);
>   	if (!mhi_cntrl->mhi_event)
>   		return -ENOMEM;
> 
> --
> 2.25.1
>