| Message ID | ee3248f9f8d60cff9106a5a46c5f5d53ac81e60a.1719771133.git.lukas@wunner.de |
|---|---|
| State | New |
| Headers | show |
| Series | PCI device authentication | expand |
On Sun, 30 Jun 2024 21:53:00 +0200 Lukas Wunner <lukas@wunner.de> wrote: > Remote attestation services may mistrust the kernel to always use a > fresh nonce for SPDM authentication. > > So allow user space to set the next requester nonce by writing to a > sysfs attribute. > > Signed-off-by: Lukas Wunner <lukas@wunner.de> > Cc: James Bottomley <James.Bottomley@HansenPartnership.com> > Cc: Jérôme Glisse <jglisse@google.com> > Cc: Jason Gunthorpe <jgg@nvidia.com> Why is the group visibility callback in this patch? Otherwise looks fine to me, Jonathan > --- > Documentation/ABI/testing/sysfs-devices-spdm | 29 ++++++++++++++++ > lib/spdm/core.c | 1 + > lib/spdm/req-authenticate.c | 8 ++++- > lib/spdm/req-sysfs.c | 35 ++++++++++++++++++++ > lib/spdm/spdm.h | 4 +++ > 5 files changed, 76 insertions(+), 1 deletion(-) > > diff --git a/Documentation/ABI/testing/sysfs-devices-spdm b/Documentation/ABI/testing/sysfs-devices-spdm > index 5ce34ce10b9c..d315b47b4af0 100644 > --- a/Documentation/ABI/testing/sysfs-devices-spdm > +++ b/Documentation/ABI/testing/sysfs-devices-spdm > @@ -216,3 +216,32 @@ Description: > necessary to parse the SPDM messages in the transcript to find > and extract the nonces, which is cumbersome. That's why they > are exposed as separate files. > + > + > +What: /sys/devices/.../signatures/next_requester_nonce > +Date: June 2024 > +Contact: Lukas Wunner <lukas@wunner.de> > +Description: > + If you do not trust the kernel to always use a fresh nonce, > + write 32 bytes to this file to set the requester nonce used > + in the next SPDM authentication sequence. > + > + Meant for remote attestation services. You are responsible > + for providing a nonce with sufficient entropy. The kernel > + only uses the nonce once, so provide a new one every time > + you reauthenticate the device. If you do not provide a > + nonce, the kernel generates a random one. > + > + After the nonce has been consumed, it becomes readable as > + the newest [0-9]*_requester_nonce, which proves its usage:: > + > + # dd if=/dev/random bs=32 count=1 | \ > + tee signatures/next_requester_nonce | hexdump > + 0000000 e0 77 91 54 bd 56 99 c2 ea 4f 0b 1a 7f ba 6e 59 > + 0000010 8f ee f6 b2 26 82 58 34 9e e5 8c 8a 31 58 29 7e > + > + # echo re > authenticated > + > + # hexdump $(\ls -t signatures/[0-9]*_requester_nonce | head -1) > + 0000000 e0 77 91 54 bd 56 99 c2 ea 4f 0b 1a 7f ba 6e 59 > + 0000010 8f ee f6 b2 26 82 58 34 9e e5 8c 8a 31 58 29 7e > diff --git a/lib/spdm/core.c b/lib/spdm/core.c > index b6a46bdbb2f9..7371adb7a52f 100644 > --- a/lib/spdm/core.c > +++ b/lib/spdm/core.c > @@ -434,6 +434,7 @@ void spdm_destroy(struct spdm_state *spdm_state) > spdm_reset(spdm_state); > spdm_destroy_log(spdm_state); > mutex_destroy(&spdm_state->lock); > + kfree(spdm_state->next_nonce); > kfree(spdm_state); > } > EXPORT_SYMBOL_GPL(spdm_destroy); > diff --git a/lib/spdm/req-authenticate.c b/lib/spdm/req-authenticate.c > index 7c977f5835c1..489fc88de74d 100644 > --- a/lib/spdm/req-authenticate.c > +++ b/lib/spdm/req-authenticate.c > @@ -626,7 +626,13 @@ static int spdm_challenge(struct spdm_state *spdm_state, u8 slot, bool verify) > }; > int rc, length; > > - get_random_bytes(&req.nonce, sizeof(req.nonce)); > + if (spdm_state->next_nonce) { > + memcpy(&req.nonce, spdm_state->next_nonce, sizeof(req.nonce)); > + kfree(spdm_state->next_nonce); > + spdm_state->next_nonce = NULL; > + } else { > + get_random_bytes(&req.nonce, sizeof(req.nonce)); > + } > > if (spdm_state->version <= 0x12) > req_sz = offsetofend(typeof(req), nonce); > diff --git a/lib/spdm/req-sysfs.c b/lib/spdm/req-sysfs.c > index c782054f8e18..232d4a00a510 100644 > --- a/lib/spdm/req-sysfs.c > +++ b/lib/spdm/req-sysfs.c > @@ -176,13 +176,48 @@ const struct attribute_group spdm_certificates_group = { > > /* signatures attributes */ > > +static umode_t spdm_signatures_are_visible(struct kobject *kobj, > + struct bin_attribute *a, int n) > +{ > + struct device *dev = kobj_to_dev(kobj); > + struct spdm_state *spdm_state = dev_to_spdm_state(dev); > + > + if (IS_ERR_OR_NULL(spdm_state)) > + return SYSFS_GROUP_INVISIBLE; > + > + return a->attr.mode; > +} > + > +static ssize_t next_requester_nonce_write(struct file *file, > + struct kobject *kobj, > + struct bin_attribute *attr, > + char *buf, loff_t off, size_t count) > +{ > + struct device *dev = kobj_to_dev(kobj); > + struct spdm_state *spdm_state = dev_to_spdm_state(dev); > + > + guard(mutex)(&spdm_state->lock); > + > + if (!spdm_state->next_nonce) { > + spdm_state->next_nonce = kmalloc(SPDM_NONCE_SZ, GFP_KERNEL); > + if (!spdm_state->next_nonce) > + return -ENOMEM; > + } > + > + memcpy(spdm_state->next_nonce + off, buf, count); > + return count; > +} > +static BIN_ATTR_WO(next_requester_nonce, SPDM_NONCE_SZ); > + > static struct bin_attribute *spdm_signatures_bin_attrs[] = { > + &bin_attr_next_requester_nonce, > NULL > }; > > const struct attribute_group spdm_signatures_group = { > .name = "signatures", > .bin_attrs = spdm_signatures_bin_attrs, > + .is_bin_visible = spdm_signatures_are_visible, > }; > > static unsigned int spdm_max_log_sz = SZ_16M; /* per device */ > diff --git a/lib/spdm/spdm.h b/lib/spdm/spdm.h > index 448107c92db7..aa36aa55e718 100644 > --- a/lib/spdm/spdm.h > +++ b/lib/spdm/spdm.h > @@ -475,6 +475,9 @@ struct spdm_error_rsp { > * itself and the transcript with trailing signature. > * @log_counter: Number of generated log entries so far. Will be prefixed to > * the sysfs files of the next generated log entry. > + * @next_nonce: Requester nonce to be used for the next authentication > + * sequence. Populated from user space through sysfs. > + * If user space does not provide a nonce, the kernel uses a random one. > */ > struct spdm_state { > struct device *dev; > @@ -521,6 +524,7 @@ struct spdm_state { > struct list_head log; > size_t log_sz; > u32 log_counter; > + u8 *next_nonce; > }; > > extern struct list_head spdm_state_list;
diff --git a/Documentation/ABI/testing/sysfs-devices-spdm b/Documentation/ABI/testing/sysfs-devices-spdm index 5ce34ce10b9c..d315b47b4af0 100644 --- a/Documentation/ABI/testing/sysfs-devices-spdm +++ b/Documentation/ABI/testing/sysfs-devices-spdm @@ -216,3 +216,32 @@ Description: necessary to parse the SPDM messages in the transcript to find and extract the nonces, which is cumbersome. That's why they are exposed as separate files. + + +What: /sys/devices/.../signatures/next_requester_nonce +Date: June 2024 +Contact: Lukas Wunner <lukas@wunner.de> +Description: + If you do not trust the kernel to always use a fresh nonce, + write 32 bytes to this file to set the requester nonce used + in the next SPDM authentication sequence. + + Meant for remote attestation services. You are responsible + for providing a nonce with sufficient entropy. The kernel + only uses the nonce once, so provide a new one every time + you reauthenticate the device. If you do not provide a + nonce, the kernel generates a random one. + + After the nonce has been consumed, it becomes readable as + the newest [0-9]*_requester_nonce, which proves its usage:: + + # dd if=/dev/random bs=32 count=1 | \ + tee signatures/next_requester_nonce | hexdump + 0000000 e0 77 91 54 bd 56 99 c2 ea 4f 0b 1a 7f ba 6e 59 + 0000010 8f ee f6 b2 26 82 58 34 9e e5 8c 8a 31 58 29 7e + + # echo re > authenticated + + # hexdump $(\ls -t signatures/[0-9]*_requester_nonce | head -1) + 0000000 e0 77 91 54 bd 56 99 c2 ea 4f 0b 1a 7f ba 6e 59 + 0000010 8f ee f6 b2 26 82 58 34 9e e5 8c 8a 31 58 29 7e diff --git a/lib/spdm/core.c b/lib/spdm/core.c index b6a46bdbb2f9..7371adb7a52f 100644 --- a/lib/spdm/core.c +++ b/lib/spdm/core.c @@ -434,6 +434,7 @@ void spdm_destroy(struct spdm_state *spdm_state) spdm_reset(spdm_state); spdm_destroy_log(spdm_state); mutex_destroy(&spdm_state->lock); + kfree(spdm_state->next_nonce); kfree(spdm_state); } EXPORT_SYMBOL_GPL(spdm_destroy); diff --git a/lib/spdm/req-authenticate.c b/lib/spdm/req-authenticate.c index 7c977f5835c1..489fc88de74d 100644 --- a/lib/spdm/req-authenticate.c +++ b/lib/spdm/req-authenticate.c @@ -626,7 +626,13 @@ static int spdm_challenge(struct spdm_state *spdm_state, u8 slot, bool verify) }; int rc, length; - get_random_bytes(&req.nonce, sizeof(req.nonce)); + if (spdm_state->next_nonce) { + memcpy(&req.nonce, spdm_state->next_nonce, sizeof(req.nonce)); + kfree(spdm_state->next_nonce); + spdm_state->next_nonce = NULL; + } else { + get_random_bytes(&req.nonce, sizeof(req.nonce)); + } if (spdm_state->version <= 0x12) req_sz = offsetofend(typeof(req), nonce); diff --git a/lib/spdm/req-sysfs.c b/lib/spdm/req-sysfs.c index c782054f8e18..232d4a00a510 100644 --- a/lib/spdm/req-sysfs.c +++ b/lib/spdm/req-sysfs.c @@ -176,13 +176,48 @@ const struct attribute_group spdm_certificates_group = { /* signatures attributes */ +static umode_t spdm_signatures_are_visible(struct kobject *kobj, + struct bin_attribute *a, int n) +{ + struct device *dev = kobj_to_dev(kobj); + struct spdm_state *spdm_state = dev_to_spdm_state(dev); + + if (IS_ERR_OR_NULL(spdm_state)) + return SYSFS_GROUP_INVISIBLE; + + return a->attr.mode; +} + +static ssize_t next_requester_nonce_write(struct file *file, + struct kobject *kobj, + struct bin_attribute *attr, + char *buf, loff_t off, size_t count) +{ + struct device *dev = kobj_to_dev(kobj); + struct spdm_state *spdm_state = dev_to_spdm_state(dev); + + guard(mutex)(&spdm_state->lock); + + if (!spdm_state->next_nonce) { + spdm_state->next_nonce = kmalloc(SPDM_NONCE_SZ, GFP_KERNEL); + if (!spdm_state->next_nonce) + return -ENOMEM; + } + + memcpy(spdm_state->next_nonce + off, buf, count); + return count; +} +static BIN_ATTR_WO(next_requester_nonce, SPDM_NONCE_SZ); + static struct bin_attribute *spdm_signatures_bin_attrs[] = { + &bin_attr_next_requester_nonce, NULL }; const struct attribute_group spdm_signatures_group = { .name = "signatures", .bin_attrs = spdm_signatures_bin_attrs, + .is_bin_visible = spdm_signatures_are_visible, }; static unsigned int spdm_max_log_sz = SZ_16M; /* per device */ diff --git a/lib/spdm/spdm.h b/lib/spdm/spdm.h index 448107c92db7..aa36aa55e718 100644 --- a/lib/spdm/spdm.h +++ b/lib/spdm/spdm.h @@ -475,6 +475,9 @@ struct spdm_error_rsp { * itself and the transcript with trailing signature. * @log_counter: Number of generated log entries so far. Will be prefixed to * the sysfs files of the next generated log entry. + * @next_nonce: Requester nonce to be used for the next authentication + * sequence. Populated from user space through sysfs. + * If user space does not provide a nonce, the kernel uses a random one. */ struct spdm_state { struct device *dev; @@ -521,6 +524,7 @@ struct spdm_state { struct list_head log; size_t log_sz; u32 log_counter; + u8 *next_nonce; }; extern struct list_head spdm_state_list;
Remote attestation services may mistrust the kernel to always use a fresh nonce for SPDM authentication. So allow user space to set the next requester nonce by writing to a sysfs attribute. Signed-off-by: Lukas Wunner <lukas@wunner.de> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Jérôme Glisse <jglisse@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> --- Documentation/ABI/testing/sysfs-devices-spdm | 29 ++++++++++++++++ lib/spdm/core.c | 1 + lib/spdm/req-authenticate.c | 8 ++++- lib/spdm/req-sysfs.c | 35 ++++++++++++++++++++ lib/spdm/spdm.h | 4 +++ 5 files changed, 76 insertions(+), 1 deletion(-)