From: Florian Fainelli <f.fainelli@gmail.com>
To: Joe Burmeister <joe.burmeister@devtank.co.uk>,
Mark Brown <broonie@kernel.org>, Ray Jui <rjui@broadcom.com>,
Scott Branden <sbranden@broadcom.com>,
bcm-kernel-feedback-list@broadcom.com, linux-spi@vger.kernel.org,
linux-rpi-kernel@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, nsaenz@kernel.org
Subject: Re: [PATCH] spi: bcm2835: Fix buffer overflow with CS able to go beyond limit.
Date: Thu, 22 Apr 2021 16:49:19 -0700 [thread overview]
Message-ID: <271ad212-a606-620e-3f0c-d6bff272be3c@gmail.com> (raw)
In-Reply-To: <7c9f9376-1a80-b624-7b9e-0f6d04437c02@devtank.co.uk>
On 4/22/2021 1:10 PM, Joe Burmeister wrote:
>> On 4/20/2021 1:34 AM, Joe Burmeister wrote:
>>> It was previoulsy possible to have a device tree with more chips than
>>> the driver supports and go off the end of CS arrays.
>> Do you mind walking me through the code how that could have happened? We
>> have spi_register_controller() call of_spi_get_gpio_numbers() which has
>> the following:
>>
>> ctlr->num_chipselect = max_t(int, nb, ctlr->num_chipselect);
>>
>> such that what the controller has is the maximum between the number of
>> 'cs-gpios' properties parsed and what was already populated in
>> ctrl->num_chipselect during bcm2835_spi_probe(), which for this driver
>> is BCM2835_SPI_NUM_CS (3).
>
> If you make a initial device tree (or add overlay in the rpi's
> config.txt) with more on the bus than BCM2835_SPI_NUM_CS (in my case 8
> devices), you get into this trampling memory state. As the devices are
> added, once the chip_select is equal to or greater than
> BCM2835_SPI_NUM_CS, it's writing off the end of the arrays.
OK.
>
> There is no protection from this happening. By the looks of it, this
> isn't the only driver this could happen with, but it is the one I have
> hardware for to test. There are also drivers that look like they don't
> have a problem going well beyond the limit they gave.
Right, which means that we should probably seek a solution within the
SPI core itself, even if you can only test with spi-bcm2835.c chances
are that the fix would be applicable for other controllers if done in
the core.
>
> There is protection in spi_add_device, which will catch extra added
> later, but not ones in the device tree when the spi controller was
> registered.
Not sure I follow you, if we have the overlay before
spi_register_controller() is called, how can the check there not
trigger? And if we load the overlay later when the SPI controller is
already registered, why does not spi_add_device()'s check work?
How would I go about reproducing this on a Pi4?
>
>>> This patches inforces CS limit but sets that limit to the max of the
>>> default limit and what is in the device tree when driver is loaded.
>>>
>>> Signed-off-by: Joe Burmeister <joe.burmeister@devtank.co.uk>
>> You have changed many more things that just enforcing a limit on
>> BCM2835_SPI_NUM_CS you have now made all chip-select related data
>> structuresd dynamically allocated and you have changed a number of
>> prints to use the shorthand "dev" instead of &pdev->dev.
> The change to dynamic allocated arrays is just to support what is given
> in the device tree rather than increase and enforce the CS limit just
> for my case.
>
> The shorthand is of course not required. I'll drop it on resubmitting.
>
> Regards,
>
> Joe
>
>
--
Florian
next prev parent reply other threads:[~2021-04-22 23:49 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 8:34 [PATCH] spi: bcm2835: Fix buffer overflow with CS able to go beyond limit Joe Burmeister
2021-04-22 16:42 ` Mark Brown
2021-04-22 16:50 ` Florian Fainelli
2021-04-22 20:10 ` Joe Burmeister
2021-04-22 23:49 ` Florian Fainelli [this message]
2021-04-23 10:03 ` Joe Burmeister
2021-04-23 11:57 ` Mark Brown
2021-04-23 14:12 ` Joe Burmeister
2021-04-23 16:20 ` Mark Brown
2021-04-23 17:34 ` Nicolas Saenz Julienne
2021-05-01 19:51 ` Lukas Wunner
2021-05-04 11:51 ` Mark Brown
2021-05-04 13:53 ` Lukas Wunner
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