Messages in this thread | | | Date | Tue, 3 Oct 2023 12:29:42 -0700 | Subject | Re: [PATCH v4 6/6] virt: tdx-guest: Add Quote generation support using TSM_REPORTS | From | Kuppuswamy Sathyanarayanan <> |
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Hi,
On 10/3/2023 11:37 AM, Peter Gonda wrote: > 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. >
Dan, do you think it is related to not allocating direct mapped memory (using kvalloc)?
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
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