linux-kernel - Re: [PATCH v2 6/6] dmaengine: pl330: Make sure microcode is privileged-executable

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Date:	Mon, 11 Jul 2016 16:23:53 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	Mitchel Humpherys <mitchelh@...eaurora.org>,
	iommu@...ts.linux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Will Deacon <will.deacon@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	Jordan Crouse <jcrouse@...eaurora.org>,
	Jeremy Gebben <jgebben@...eaurora.org>,
	Patrick Daly <pdaly@...eaurora.org>,
	Pratik Patel <pratikp@...eaurora.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Jassi Brar <jassi.brar@...sung.com>
Subject: Re: [PATCH v2 6/6] dmaengine: pl330: Make sure microcode is
 privileged-executable

On 09/07/16 03:09, Mitchel Humpherys wrote:
> The PL330 can perform privileged instruction fetches.  This can result

Nit: "can" is a bit of an understatement. Instruction fetches on both
the manager and channel threads have the "privileged" and "instruction"
AxPROT bits hard-coded whether you like it or not. It's only the data
accesses by the channel threads which are in any way configurable.

Robin.

> in SMMU permission faults on SMMUs that implement the ARMv8 VMSA, which
> specifies that mappings that are writeable at one execution level shall
> not be executable at any higher-privileged level.  Fix this by using the
> DMA_ATTR_PRIVILEGED_EXECUTABLE attribute, which will ensure that the
> microcode IOMMU mapping is not writeable.
> 
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Jassi Brar <jassi.brar@...sung.com>
> Signed-off-by: Mitchel Humpherys <mitchelh@...eaurora.org>
> ---
>  drivers/dma/pl330.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 372b4359da97..25bc49d47c45 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -1854,14 +1854,17 @@ static int dmac_alloc_resources(struct pl330_dmac *pl330)
>  {
>  	int chans = pl330->pcfg.num_chan;
>  	int ret;
> +	DEFINE_DMA_ATTRS(attrs);
>  
> +	dma_set_attr(DMA_ATTR_PRIVILEGED_EXECUTABLE, &attrs);
>  	/*
>  	 * Alloc MicroCode buffer for 'chans' Channel threads.
>  	 * A channel's buffer offset is (Channel_Id * MCODE_BUFF_PERCHAN)
>  	 */
> -	pl330->mcode_cpu = dma_alloc_coherent(pl330->ddma.dev,
> +	pl330->mcode_cpu = dma_alloc_attrs(pl330->ddma.dev,
>  				chans * pl330->mcbufsz,
> -				&pl330->mcode_bus, GFP_KERNEL);
> +				&pl330->mcode_bus, GFP_KERNEL,
> +				&attrs);
>  	if (!pl330->mcode_cpu) {
>  		dev_err(pl330->ddma.dev, "%s:%d Can't allocate memory!\n",
>  			__func__, __LINE__);
>