Messages in this thread | | | From | Peter Gonda <> | Date | Tue, 3 Oct 2023 12:37:00 -0600 | Subject | Re: [PATCH v4 6/6] virt: tdx-guest: Add Quote generation support using TSM_REPORTS |
| |
On Fri, Sep 29, 2023 at 11:26 AM Peter Gonda <pgonda@google.com> wrote: > > On Thu, Sep 28, 2023 at 4:49 PM Dan Williams <dan.j.williams@intel.com> wrote: > > > > Peter Gonda wrote: > > > On Mon, Sep 25, 2023 at 10:17 PM Dan Williams <dan.j.williams@intel.com> wrote: > > > > > > > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> > > > > > > > > In TDX guest, the attestation process is used to verify the TDX guest > > > > trustworthiness to other entities before provisioning secrets to the > > > > guest. The first step in the attestation process is TDREPORT > > > > generation, which involves getting the guest measurement data in the > > > > format of TDREPORT, which is further used to validate the authenticity > > > > of the TDX guest. TDREPORT by design is integrity-protected and can > > > > only be verified on the local machine. > > > > > > > > To support remote verification of the TDREPORT in a SGX-based > > > > attestation, the TDREPORT needs to be sent to the SGX Quoting Enclave > > > > (QE) to convert it to a remotely verifiable Quote. SGX QE by design can > > > > only run outside of the TDX guest (i.e. in a host process or in a > > > > normal VM) and guest can use communication channels like vsock or > > > > TCP/IP to send the TDREPORT to the QE. But for security concerns, the > > > > TDX guest may not support these communication channels. To handle such > > > > cases, TDX defines a GetQuote hypercall which can be used by the guest > > > > to request the host VMM to communicate with the SGX QE. More details > > > > about GetQuote hypercall can be found in TDX Guest-Host Communication > > > > Interface (GHCI) for Intel TDX 1.0, section titled > > > > "TDG.VP.VMCALL<GetQuote>". > > > > > > > > Trusted Security Module (TSM) [1] exposes a common ABI for Confidential > > > > Computing Guest platforms to get the measurement data via ConfigFS. > > > > Extend the TSM framework and add support to allow an attestation agent > > > > to get the TDX Quote data (included usage example below). > > > > > > > > report=/sys/kernel/config/tsm/report/report0 > > > > mkdir $report > > > > dd if=/dev/urandom bs=64 count=1 > $report/inblob > > > > hexdump -C $report/outblob > > > > rmdir $report > > > > > > > > GetQuote TDVMCALL requires TD guest pass a 4K aligned shared buffer > > > > with TDREPORT data as input, which is further used by the VMM to copy > > > > the TD Quote result after successful Quote generation. To create the > > > > shared buffer, allocate a large enough memory and mark it shared using > > > > set_memory_decrypted() in tdx_guest_init(). This buffer will be re-used > > > > for GetQuote requests in the TDX TSM handler. > > > > > > > > Although this method reserves a fixed chunk of memory for GetQuote > > > > requests, such one time allocation can help avoid memory fragmentation > > > > related allocation failures later in the uptime of the guest. > > > > > > > > Since the Quote generation process is not time-critical or frequently > > > > used, the current version uses a polling model for Quote requests and > > > > it also does not support parallel GetQuote requests. > > > > > > > > Link: https://lore.kernel.org/lkml/169342399185.3934343.3035845348326944519.stgit@dwillia2-xfh.jf.intel.com/ [1] > > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> > > > > Reviewed-by: Erdem Aktas <erdemaktas@google.com> > > > > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > > > > > > Hey Dan, > > > > > > I tried running your test commands on an SNP enabled guest. To build > > > the kernel I just checked out linus/master and applied your series. I > > > haven't done any debugging yet, so I will update with what I find. > > > > > > root@Ubuntu2004:~# hexdump -C $report/outblob > > > [ 219.871875] ------------[ cut here ]------------ > > > [ 219.876642] kernel BUG at include/linux/scatterlist.h:187! > > > > Ok, it does not like virtual address of one of the buffers, but my > > changes "should" not have affected that as get_ext_report() internally > > uses snp_dev->certs_data and snp_dev->response for bounce buffering the > > actual request / response memory. First test I want to try once I can > > get on an SNP system is compare this to the ioctl path just make sure > > that succeeds. >
I think there may be an issue with CONFIG_DEBUG_SG. That was the warning we were getting in my above stack trace:
> [ 219.876642] kernel BUG at include/linux/scatterlist.h:187!
This was for this line in enc_dec_message():
sg_set_buf(&src[1], src_buf, hdr->msg_sz);
I am not sure why in sg_set_buf() virt_addr_valid() returns false for the address given in the sev_report_new() which is from the variable 'ext_req' which is stack allocated?
static inline void sg_set_buf(struct scatterlist *sg, const void *buf, unsigned int buflen) { #ifdef CONFIG_DEBUG_SG BUG_ON(!virt_addr_valid(buf)); #endif sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf)); }
When I disable CONFIG_DEBUG_SG in my config. Your patch seems to work, well at least it doesn't crash the guest. I haven't checked if the report is valid yet.
| |