* [PATCH v4] xen: detect uninitialized xenbus in xenbus_init
@ 2021-11-23 21:07 Stefano Stabellini
2021-11-24 5:11 ` Juergen Gross
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Stefano Stabellini @ 2021-11-23 21:07 UTC (permalink / raw)
To: jgross
Cc: boris.ostrovsky, xen-devel, linux-kernel, sstabellini, jbeulich,
Stefano Stabellini, stable
From: Stefano Stabellini <stefano.stabellini@xilinx.com>
If the xenstore page hasn't been allocated properly, reading the value
of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return
error. Instead, it will succeed and return zero. Instead of attempting
to xen_remap a bad guest physical address, detect this condition and
return early.
Note that although a guest physical address of zero for
HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice
and zero has never been validly used in that capacity.
Also recognize all bits set as an invalid value.
For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns
above ULONG_MAX should never be passed by the Xen tools to HVM guests
anyway, so check for this condition and return early.
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
---
Changes in v4:
- say "all bits set" instead of INVALID_PFN
- improve check
Changes in v3:
- improve in-code comment
- improve check
Changes in v2:
- add check for ULLONG_MAX (unitialized)
- add check for ULONG_MAX #if BITS_PER_LONG == 32 (actual error)
- add pr_err error message
drivers/xen/xenbus/xenbus_probe.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 94405bb3829e..251b26439733 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -951,6 +951,29 @@ 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.
+ *
+ * Also recognize all bits set as an invalid value.
+ */
+ if (!v || !~v) {
+ err = -ENOENT;
+ goto out_error;
+ }
+ /* Avoid truncation on 32-bit. */
+#if BITS_PER_LONG == 32
+ if (v > ULONG_MAX) {
+ pr_err("%s: cannot handle HVM_PARAM_STORE_PFN=%llx > ULONG_MAX\n",
+ __func__, v);
+ err = -EINVAL;
+ goto out_error;
+ }
+#endif
xen_store_gfn = (unsigned long)v;
xen_store_interface =
xen_remap(xen_store_gfn << XEN_PAGE_SHIFT,
--
2.25.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v4] xen: detect uninitialized xenbus in xenbus_init
2021-11-23 21:07 [PATCH v4] xen: detect uninitialized xenbus in xenbus_init Stefano Stabellini
@ 2021-11-24 5:11 ` Juergen Gross
2021-11-24 7:33 ` Jan Beulich
2021-11-25 15:20 ` Boris Ostrovsky
2 siblings, 0 replies; 4+ messages in thread
From: Juergen Gross @ 2021-11-24 5:11 UTC (permalink / raw)
To: Stefano Stabellini
Cc: boris.ostrovsky, xen-devel, linux-kernel, jbeulich,
Stefano Stabellini, stable
[-- Attachment #1.1.1: Type: text/plain, Size: 1039 bytes --]
On 23.11.21 22:07, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xilinx.com>
>
> If the xenstore page hasn't been allocated properly, reading the value
> of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return
> error. Instead, it will succeed and return zero. Instead of attempting
> to xen_remap a bad guest physical address, detect this condition and
> return early.
>
> Note that although a guest physical address of zero for
> HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice
> and zero has never been validly used in that capacity.
>
> Also recognize all bits set as an invalid value.
>
> For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns
> above ULONG_MAX should never be passed by the Xen tools to HVM guests
> anyway, so check for this condition and return early.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Juergen
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v4] xen: detect uninitialized xenbus in xenbus_init
2021-11-23 21:07 [PATCH v4] xen: detect uninitialized xenbus in xenbus_init Stefano Stabellini
2021-11-24 5:11 ` Juergen Gross
@ 2021-11-24 7:33 ` Jan Beulich
2021-11-25 15:20 ` Boris Ostrovsky
2 siblings, 0 replies; 4+ messages in thread
From: Jan Beulich @ 2021-11-24 7:33 UTC (permalink / raw)
To: Stefano Stabellini
Cc: boris.ostrovsky, xen-devel, linux-kernel, Stefano Stabellini,
stable, jgross
On 23.11.2021 22:07, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xilinx.com>
>
> If the xenstore page hasn't been allocated properly, reading the value
> of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return
> error. Instead, it will succeed and return zero. Instead of attempting
> to xen_remap a bad guest physical address, detect this condition and
> return early.
>
> Note that although a guest physical address of zero for
> HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice
> and zero has never been validly used in that capacity.
>
> Also recognize all bits set as an invalid value.
>
> For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns
> above ULONG_MAX should never be passed by the Xen tools to HVM guests
> anyway, so check for this condition and return early.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v4] xen: detect uninitialized xenbus in xenbus_init
2021-11-23 21:07 [PATCH v4] xen: detect uninitialized xenbus in xenbus_init Stefano Stabellini
2021-11-24 5:11 ` Juergen Gross
2021-11-24 7:33 ` Jan Beulich
@ 2021-11-25 15:20 ` Boris Ostrovsky
2 siblings, 0 replies; 4+ messages in thread
From: Boris Ostrovsky @ 2021-11-25 15:20 UTC (permalink / raw)
To: Stefano Stabellini, jgross
Cc: xen-devel, linux-kernel, jbeulich, Stefano Stabellini, stable
On 11/23/21 4:07 PM, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xilinx.com>
>
> If the xenstore page hasn't been allocated properly, reading the value
> of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return
> error. Instead, it will succeed and return zero. Instead of attempting
> to xen_remap a bad guest physical address, detect this condition and
> return early.
>
> Note that although a guest physical address of zero for
> HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice
> and zero has never been validly used in that capacity.
>
> Also recognize all bits set as an invalid value.
>
> For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns
> above ULONG_MAX should never be passed by the Xen tools to HVM guests
> anyway, so check for this condition and return early.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Applied to for-linus-5.16c
-boris
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-11-23 21:07 [PATCH v4] xen: detect uninitialized xenbus in xenbus_init Stefano Stabellini
2021-11-24 5:11 ` Juergen Gross
2021-11-24 7:33 ` Jan Beulich
2021-11-25 15:20 ` Boris Ostrovsky
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