netdev - Re: [PATCH net 1/2] net: stmmac: est: Fix GCL bounds checks

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Message-ID: <20250911170159.383edcc6@kernel.org>
Date: Thu, 11 Sep 2025 17:01:59 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "G Thomas, Rohan" <rohan.g.thomas@...era.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Maxime
 Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Jose Abreu <Jose.Abreu@...opsys.com>, Rohan
 G Thomas <rohan.g.thomas@...el.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Matthew
 Gerlach <matthew.gerlach@...era.com>
Subject: Re: [PATCH net 1/2] net: stmmac: est: Fix GCL bounds checks

On Thu, 11 Sep 2025 18:12:16 +0530 G Thomas, Rohan wrote:
> On 9/11/2025 4:54 PM, Russell King (Oracle) wrote:
> > On Thu, Sep 11, 2025 at 04:22:59PM +0800, Rohan G Thomas via B4 Relay wrote:  
> >> @@ -1012,7 +1012,7 @@ static int tc_taprio_configure(struct stmmac_priv *priv,
> >>   		s64 delta_ns = qopt->entries[i].interval;
> >>   		u32 gates = qopt->entries[i].gate_mask;
> >>   
> >> -		if (delta_ns > GENMASK(wid, 0))
> >> +		if (delta_ns >= BIT(wid))  
> > 
> > While I agree this makes it look better, you don't change the version
> > below, which makes the code inconsistent. I also don't see anything
> > wrong with the original comparison.  
> 
> Just to clarify the intent behind this change:
> For example, if wid = 3, then GENMASK(3, 0) = 0b1111 = 15. But the
> maximum supported gate interval in this case is actually 7, since only 3
> bits are available to represent the value. So in the patch, the
> condition delta_ns >= BIT(wid) effectively checks if delta_ns is 8 or
> more, which correctly returns an error for values that exceed the 3-bit
> limit.

Comparison to BIT() looks rather odd, I think it's better to correct
the GENMASK() bound?