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Re: [Qemu-block] [Qemu-devel] [PATCH] qcow2: Assert that L2 table offset

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH] qcow2: Assert that L2 table offsets fit in the L1 table
Date: Fri, 8 Feb 2019 09:50:05 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

On 2/8/19 9:44 AM, Alberto Garcia wrote:
> L1 table entries have a field to store the offset of an L2 table.
> The rest of the bits of the entry are currently reserved except from
> bit 63, which stores the COPIED flag.
> The offset is always taken from the entry using L1E_OFFSET_MASK to
> ensure that we only use the bits that belong to that field.
> While that mask is used every time we read from the L1 table, it is
> never used when we write to it. Due to the limits set elsewhere in the
> code QEMU can never produce L2 table offsets that don't fit in that
> field so any such offset when allocating an L2 table would indicate a
> bug in QEMU.
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/qcow2-cluster.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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