linux-kernel - Re: [PATCH 6.1 v2 0/3] aic79xx: Add some non-NULL checks

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Message-ID: <a9c3ed6d6fac804a2f146288039228a9745d70bb.camel@HansenPartnership.com>
Date: Mon, 28 Apr 2025 08:07:41 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Boris Belyavtsev <bbelyavtsev@...rgate.com>, hare@...e.com
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	lvc-project@...uxtesting.org
Subject: Re: [PATCH 6.1 v2 0/3] aic79xx: Add some non-NULL checks

On Mon, 2025-04-28 at 11:32 +0700, Boris Belyavtsev wrote:
> On Mon Apr 21, 2025 at 7:12 PM +07, James Bottomley wrote:
> > On Mon, 2025-04-21 at 15:16 +0700, Boris Belyavtsev wrote:
> > > Add non-NULL checks for ahd_lookup_scb return value.
> > > 
> > > scb could be NULL if faulty hardware return certain incorrect
> > > values to the driver.
> > 
> > It's a general principle that we trust values coming from the card
> > ... you are, after all, trusting it with your data.  If there's a
> > fault in the way the card is operating, we can work around that, so
> > if you have a card which is producing these NULLs, can you provide
> > details so we can investigate?
> > 
> > Regards,
> > 
> > James
> 
> Well, to be honest, I do not have such a device/card which would
> represent the problem. These checks are more about defensive
> programming (in case of an accident fault in a card for example).

We don't program defensively against adapters: they're part of our
trust domain.  We only program defensively against input from untrusted
domains (like user space).  The problem with defensively programming
drivers was nicely demonstrated by the driver hardening project:

https://lore.kernel.org/all/20230119170633.40944-1-alexander.shishkin@linux.intel.com/

In that there are so many ways that drivers could be used to attack the
OS, defending against all of them would dramatically impact the fast
path.  Which is also the reason we don't imagine card faults and then
program for them without first finding the problem in the field.

Regards,

James