linux-kernel - Re: [PATCH 1/1] swiotlb: fix out-of-bounds TLB allocations with CONFIG_SWIOTLB

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Message-ID: <20231109160517.3d1c1e17@meshulam.tesarici.cz>
Date:   Thu, 9 Nov 2023 16:05:17 +0100
From:   Petr Tesařík <petr@...arici.cz>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Petr Tesarik <petrtesarik@...weicloud.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Petr Tesarik <petr.tesarik.ext@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
        open list <linux-kernel@...r.kernel.org>,
        Wangkefeng <wangkefeng.wang@...wei.com>,
        Roberto Sassu <roberto.sassu@...weicloud.com>,
        Petr Tesarik <petr.tesarik1@...wei-partners.com>,
        Halil Pasic <pasic@...ux.ibm.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/1] swiotlb: fix out-of-bounds TLB allocations with
 CONFIG_SWIOTLB_DYNAMIC

On Thu, 09 Nov 2023 13:24:48 +0100
Niklas Schnelle <schnelle@...ux.ibm.com> wrote:

> On Wed, 2023-11-08 at 13:21 +0100, Petr Tesařík wrote:
> > On Wed,  8 Nov 2023 12:12:49 +0100
> > Petr Tesarik <petrtesarik@...weicloud.com> wrote:
> >   
> > > From: Petr Tesarik <petr.tesarik1@...wei-partners.com>
> > > 
> > > Limit the free list length to the size of the IO TLB. Transient pool can be
> > > smaller than IO_TLB_SEGSIZE, but the free list is initialized with the
> > > assumption that the total number of slots is a multiple of IO_TLB_SEGSIZE.
> > > As a result, swiotlb_area_find_slots() may allocate slots past the end of
> > > a transient IO TLB buffer.  
> > 
> > Just to make it clear, this patch addresses only the memory corruption
> > reported by Niklas, without addressing the underlying issues. Where
> > corruption happened before, allocations will fail with this patch.
> > 
> > I am still looking into improving the allocation strategy itself.
> > 
> > Petr T  
> 
> I know this has already been applied but for what its worth I did
> finally manage to test this with my reproducer and the allocation
> overrun is fixed by this change. I also confirmed that at least my
> ConnectX VF TCP/IP test case seems to handle the DMA error gracefully
> enough.

Thank you for testing!

Inded, the failed request is often retried at a later time. For example
I tested with a SCSI driver, and by the time the SCSI layer retried the
request, a new standard pool was already available. But this situation
is not ideal. If nothing else, it incurs an unnecessary delay.

Petr T