From: Jan Beulich <jbeulich@suse.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: boris.ostrovsky@oracle.com, xen-devel@lists.xenproject.org,
linux-kernel@vger.kernel.org,
Stefano Stabellini <stefano.stabellini@xilinx.com>,
stable@vger.kernel.org, jgross@suse.com
Subject: Re: [PATCH] xen: detect uninitialized xenbus in xenbus_init
Date: Wed, 17 Nov 2021 08:41:56 +0100 [thread overview]
Message-ID: <2592121c-ed62-c346-5aeb-37adb6bb1982@suse.com> (raw)
In-Reply-To: <20211117021145.3105042-1-sstabellini@kernel.org>
On 17.11.2021 03:11, Stefano Stabellini wrote:
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -951,6 +951,18 @@ static int __init xenbus_init(void)
> err = hvm_get_parameter(HVM_PARAM_STORE_PFN, &v);
> if (err)
> goto out_error;
> + /*
> + * Uninitialized hvm_params are zero and return no error.
> + * Although it is theoretically possible to have
> + * HVM_PARAM_STORE_PFN set to zero on purpose, in reality it is
> + * not zero when valid. If zero, it means that Xenstore hasn't
> + * been properly initialized. Instead of attempting to map a
> + * wrong guest physical address return error.
> + */
> + if (v == 0) {
> + err = -ENOENT;
> + goto out_error;
> + }
If such a check gets added, then I think known-invalid frame numbers
should be covered at even higher a priority than zero. This would,
for example, also mean to ...
> xen_store_gfn = (unsigned long)v;
... stop silently truncating a value here.
By covering them we would then have the option to pre-fill PFN params
with, say, ~0 in the hypervisor (to clearly identify them as invalid,
rather than having to guess at the validity of 0). I haven't really
checked yet whether such a change would be compatible with existing
software ...
Jan
next prev parent reply other threads:[~2021-11-17 7:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-17 2:11 [PATCH] xen: detect uninitialized xenbus in xenbus_init Stefano Stabellini
2021-11-17 7:41 ` Jan Beulich [this message]
2021-11-18 2:37 ` Stefano Stabellini
2021-11-18 5:32 ` Juergen Gross
2021-11-18 8:47 ` Jan Beulich
2021-11-18 8:53 ` Juergen Gross
2021-11-18 21:00 ` Stefano Stabellini
2021-11-18 22:24 ` Boris Ostrovsky
2021-11-19 8:24 ` Jan Beulich
2021-11-19 5:16 ` Juergen Gross
2021-11-18 8:40 ` Jan Beulich
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