Re: [Xen-devel] [PATCH] [v2] xen: hypercall: fix out-of-bounds memcpy

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/02/18 15:03, Arnd Bergmann wrote:

Snipping deleted code to make things clearer:

> +     if (cmd > ARRAY_SIZE(physdevop_len))
> +             return -ENOSYS;
>
> +     len = physdevop_len[cmd];
> +     memcpy(&op.u, arg, len);

You'll want an array_nospec() or whatever its called these days.  This
code is SP1-leaky.

Userspace controls cmd and can retrieve len by timing how many adjacent
cache lines were pulled in my memcpy().

~Andrew

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