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Date: Sat, 21 Mar 2026 10:04:25 +0000
From: Simon Horman <horms@kernel.org>
To: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Cc: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org,
	decui@microsoft.com, longli@microsoft.com, andrew+netdev@lunn.ch,
	davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, shradhagupta@linux.microsoft.com,
	dipayanroy@linux.microsoft.com, shirazsaleem@microsoft.com,
	kotaranov@microsoft.com, yury.norov@gmail.com, kees@kernel.org,
	linux-hyperv@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next] net: mana: Use at least SZ_4K in doorbell ID
 range check
Message-ID: <20260321100425.GX74886@horms.kernel.org>
References: <20260320122107.1560839-1-ernis@linux.microsoft.com>
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In-Reply-To: <20260320122107.1560839-1-ernis@linux.microsoft.com>

On Fri, Mar 20, 2026 at 05:21:01AM -0700, Erni Sri Satya Vennela wrote:
> mana_gd_ring_doorbell() accesses doorbell offsets up to 0xFF8 + 8 = 4KB
> within a doorbell page. When db_page_size is zero, the validation check
> in mana_gd_register_device() reduces to:
>   db_page_off + 0 > bar0_size
> which passes, even though mana_gd_ring_doorbell() will access
> [db_page_off, db_page_off + 4KB) and may go beyond BAR0.
> 
> Use max(SZ_4K, db_page_size) in the range check so that a zero or
> unexpectedly small db_page_size still results in a rejection when the
> doorbell page would fall outside BAR0.

Thanks Erni,

I understand the maths here. And to that extent this change makes sense to me.
But I am curious to know how a db_page_size of zero works. I was expecting
some space is required there.

> 
> Fixes: 89fe91c65992 ("net: mana: hardening: Validate doorbell ID from GDMA_REGISTER_DEVICE response")
> Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>

...