linux-kernel - Re: [PATCH v2] iommu/dma: Fix MSI reservation allocation

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Date:   Wed, 4 Mar 2020 12:36:54 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Eric Auger <eric.auger@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Will Deacon <will@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2] iommu/dma: Fix MSI reservation allocation

On 04/03/2020 11:11 am, Marc Zyngier wrote:
> The way cookie_init_hw_msi_region() allocates the iommu_dma_msi_page
> structures doesn't match the way iommu_put_dma_cookie() frees them.
> 
> The former performs a single allocation of all the required structures,
> while the latter tries to free them one at a time. It doesn't quite
> work for the main use case (the GICv3 ITS where the range is 64kB)
> when the base granule size is 4kB.
> 
> This leads to a nice slab corruption on teardown, which is easily
> observable by simply creating a VF on a SRIOV-capable device, and
> tearing it down immediately (no need to even make use of it).
> Fortunately, this only affects systems where the ITS isn't translated
> by the SMMU, which are both rare and non-standard.
> 
> Fix it by allocating iommu_dma_msi_page structures one at a time.

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Fixes: 7c1b058c8b5a3 ("iommu/dma: Handle IOMMU API reserved regions")
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Reviewed-by: Eric Auger <eric.auger@...hat.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Will Deacon <will@...nel.org>
> Cc: stable@...r.kernel.org
> ---
> * From v1:
>    - Got rid of the superfluous error handling (Robin)
>    - Clarified that it only affects a very small set of systems
>    - Added Eric's RB (which I assume still stands)
> 
>   drivers/iommu/dma-iommu.c | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index a2e96a5fd9a7..ba128d1cdaee 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -177,15 +177,15 @@ static int cookie_init_hw_msi_region(struct iommu_dma_cookie *cookie,
>   	start -= iova_offset(iovad, start);
>   	num_pages = iova_align(iovad, end - start) >> iova_shift(iovad);
>   
> -	msi_page = kcalloc(num_pages, sizeof(*msi_page), GFP_KERNEL);
> -	if (!msi_page)
> -		return -ENOMEM;
> -
>   	for (i = 0; i < num_pages; i++) {
> -		msi_page[i].phys = start;
> -		msi_page[i].iova = start;
> -		INIT_LIST_HEAD(&msi_page[i].list);
> -		list_add(&msi_page[i].list, &cookie->msi_page_list);
> +		msi_page = kmalloc(sizeof(*msi_page), GFP_KERNEL);
> +		if (!msi_page)
> +			return -ENOMEM;
> +
> +		msi_page->phys = start;
> +		msi_page->iova = start;
> +		INIT_LIST_HEAD(&msi_page->list);
> +		list_add(&msi_page->list, &cookie->msi_page_list);
>   		start += iovad->granule;
>   	}
>   
>