linux-kernel - Re: [PATCH 12/16] nvme-pci: Check DMA ops when indicating support for PCI P2PDMA

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <db17d695-eab8-9078-4878-dcc0ece94d23@nvidia.com>
Date:   Mon, 3 May 2021 17:17:48 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>
CC:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 12/16] nvme-pci: Check DMA ops when indicating support for
 PCI P2PDMA

On 5/3/21 10:17 AM, Logan Gunthorpe wrote:
...
>>>    	blk_queue_flag_set(QUEUE_FLAG_NONROT, ns->queue);
>>> -	if (ctrl->ops->flags & NVME_F_PCI_P2PDMA)
>>> +	if (ctrl->ops->supports_pci_p2pdma &&
>>> +	    ctrl->ops->supports_pci_p2pdma(ctrl))
>>
>> This is a little excessive, as I suspected. How about providing a
>> default .supports_pci_p2pdma routine that returns false, so that
>> the op is always available (non-null)? By "default", maybe that
>> means either requiring an init_the_ops_struct() routine to be
>> used, and/or checking all the users of struct nvme_ctrl_ops.
> 
> Honestly that sounds much more messy to me than simply checking if it's
> NULL before using it (which is a common, accepted pattern for ops).

OK, it's a minor suggestion, so feel free to ignore if you prefer it
the other way, sure.

> 
>> Another idea: maybe you don't really need a bool .supports_pci_p2pdma()
>> routine at all, because the existing .flags really is about right.
>> You just need the flags to be filled in dynamically. So, do that
>> during nvme_pci setup/init time: that's when this module would call
>> dma_pci_p2pdma_supported().
> 
> If the flag is filled in dynamically, then the ops struct would have to
> be non-constant. Ops structs should be constant for security reasons.
> 

Hadn't thought about keeping ops structs constant. OK.

thanks,
-- 
John Hubbard
NVIDIA