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: Thu, 18 Nov 2021 09:40:42 +0100 [thread overview]
Message-ID: <4c952e5b-a136-3fda-810c-29fa556ef965@suse.com> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2111171823160.1412361@ubuntu-linux-20-04-desktop>
On 18.11.2021 03:37, Stefano Stabellini wrote:
> On Wed, 17 Nov 2021, Jan Beulich wrote:
>> 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.
>
> Uhm, that's a good point. We could check for 0 and also ULONG_MAX
Why ULONG_MAX? The upper bound is determined by the number of physical
address bits (in a guest: the virtual counterpart thereof). In a 32-bit
environment ULONG_MAX could in principle even represent a valid frame
number.
Jan
prev parent reply other threads:[~2021-11-18 8:42 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
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 [this message]
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