Messages in this thread | | | Subject | Re: [PATCH v2 2/5] tsm: Introduce a shared ABI for attestation reports | From | Roy Hopkins <> | Date | Tue, 22 Aug 2023 08:29:05 +0100 |
| |
On Mon, 2023-08-14 at 00:43 -0700, Dan Williams wrote: > One of the common operations of a TSM (Trusted Security Module) is to > provide a way for a TVM (confidential computing guest execution > environment) to take a measurement of its launch state, sign it and > submit it to a verifying party. Upon successful attestation that > verifies the integrity of the TVM additional secrets may be deployed. > The concept is common across TSMs, but the implementations are > unfortunately vendor specific. While the industry grapples with a common > definition of this attestation format [1], Linux need not make this > problem worse by defining a new ABI per TSM that wants to perform a > similar operation. The current momentum has been to invent new ioctl-ABI > per TSM per function which at best is an abdication of the kernel's > responsibility to make common infrastructure concepts share common ABI. > > The proposal, targeted to conceptually work with TDX, SEV, COVE if not > more, is to define a sysfs interface to retrieve the TSM-specific blob. > > echo $hex_encoded_userdata_plus_nonce > /sys/class/tsm/tsm0/inhex > hexdump /sys/class/tsm/tsm0/outblob > > This approach later allows for the standardization of the attestation > blob format without needing to change the Linux ABI. Until then, the > format of 'outblob' is determined by the parent device for 'tsm0'. > > The expectation is that this is a boot time exchange that need not be > regenerated, making it amenable to a sysfs interface. In case userspace > does try to generate multiple attestation reports it includes conflict > detection so userspace can be sure no other thread changed the > parameters from its last configuration step to the blob retrieval. > > TSM specific options are encoded as 'extra' attributes on the TSM device > with the expectation that vendors reuse the same options for similar > concepts. The current options are defined by SEV-SNP's need for a > 'privilege level' concept (VMPL), and the option to retrieve a > certificate chain in addition to the attestation report ("extended" > format). > > Link: > http://lore.kernel.org/r/64961c3baf8ce_142af829436@dwillia2-xfh.jf.intel.com.notmuch > [1] > Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> > Cc: Dionna Amalie Glaze <dionnaglaze@google.com> > Cc: James Bottomley <James.Bottomley@HansenPartnership.com> > Cc: Peter Gonda <pgonda@google.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Samuel Ortiz <sameo@rivosinc.com> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > --- > Documentation/ABI/testing/sysfs-class-tsm | 47 +++++ > MAINTAINERS | 8 + > drivers/virt/coco/Kconfig | 4 > drivers/virt/coco/Makefile | 1 > drivers/virt/coco/tdx-guest/Kconfig | 1 > drivers/virt/coco/tsm.c | 290 > +++++++++++++++++++++++++++++ > include/linux/tsm.h | 45 +++++ > 7 files changed, 396 insertions(+) > create mode 100644 Documentation/ABI/testing/sysfs-class-tsm > create mode 100644 drivers/virt/coco/tsm.c > create mode 100644 include/linux/tsm.h
> +static ssize_t outblob_read(struct file *f, struct kobject *kobj, > + struct bin_attribute *bin_attr, char *buf, > + loff_t offset, size_t count) > +{ > + guard(rwsem_read)(&tsm_rwsem); > + if (!tsm_report.desc.inblob_len) > + return -EINVAL; > + > + if (!tsm_report.outblob || > + tsm_report.read_generation != tsm_report.write_generation) { > + const struct tsm_ops *ops = provider.ops; > + size_t outblob_len; > + u8 *outblob; > + > + kvfree(tsm_report.outblob);
I think tsm_report.outblob needs to be set to NULL here otherwise there is the possibility of a double-free if ops->report_new returns an error.
Roy
> + outblob = ops->report_new(provider.dev->parent, > + &tsm_report.desc, &outblob_len); > + if (IS_ERR(outblob)) > + return PTR_ERR(outblob); > + tsm_report.outblob_len = outblob_len; > + tsm_report.outblob = outblob; > + tsm_report.read_generation = tsm_report.write_generation; > + } > + > + return memory_read_from_buffer(buf, count, &offset, > + tsm_report.outblob, > + tsm_report.outblob_len); > +}
| |