On 23.11.2021 06:42, Juergen Gross wrote:
On 22.11.21 23:16, 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 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@vger.kernel.org Signed-off-by: Stefano Stabellini stefano.stabellini@xilinx.com
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)?
I also don't think the reference to INVALID_PFN is appropriate here. Afaict the two aren't the same on 32-bit. Plus I can't even find a constant named this way in Linux'es include/.
*/if (!v || !(v + 1)) {For me "if (!v || !~v)" would be more readable, but I don't really feel strong here.
Oh, indeed.
Jan