On 22.11.21 23:16, Stefano Stabellini wrote:
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> 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 the invalid value of INVALID_PFN which is ULLONG_MAX. 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@xxxxxxxxxxxxxxx Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> --- 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 | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c index 94405bb3829e..d3ca57d48a73 100644 --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -951,6 +951,30 @@ 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 the invalid value of INVALID_PFN which is + * ULLONG_MAX.
Adjust the comment, e.g. s/ULLONG_MAX/all bits set/ (in the commit message, too)?
+ */
+ if (!v || !(v + 1)) {
For me "if (!v || !~v)" would be more readable, but I don't really feel strong here. Juergen
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