linux-kernel - Re: [PATCH v2] swiotlb: avoid potential left shift overflow

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: <YwA8DttmM7wgYuHv@gao-cwp>
Date:   Sat, 20 Aug 2022 09:42:38 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>
CC:     <linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
        <hch@...radead.org>, <m.szyprowski@...sung.com>,
        <robin.murphy@....com>, <jxgao@...gle.com>,
        <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2] swiotlb: avoid potential left shift overflow

On Fri, Aug 19, 2022 at 06:44:05AM -0700, Dongli Zhang wrote:
>I also encountered this when sending out another version of the 64-bit swiotlb.
>
>https://lore.kernel.org/all/20220609005553.30954-8-dongli.zhang@oracle.com/
>
>Unfortunately, I could not find an environment (e.g., powerpc) to allocate more
>than 4G until swiotlb supports 64-bit.
>
>Although xen supports 64-bit, but the hypervisor side limits the max to < 4G.

Sorry. I didn't notice your series before. I agree that the overflow
isn't an issue if swiotlb size cannot be larger than 4GB. That's why
I said the overflow is a potential issue.

In an internal effort to measure the impact of swiotlb size to IO
performance of confidential VM (e.g., TDX VM), we simply added
SWIOTLB_ANY to the default io_tlb_mem to lift the restriction on swiotlb
size. Then we hit this issue and worked out this fix. I posted this
fix because I think the fix by itself is helpful because it removes the
implicit dependency of the left-shift in slot_addr() on swiotlb size and
then someone trying to lift the size limitation won't hit the same issue.