On Tue, Aug 23, 2022 at 03:25:18PM -0700, Evan Green wrote: > From: Matthew Garrett <matthewgarrett@xxxxxxxxxx> > > Under certain circumstances it might be desirable to enable the creation > of TPM-backed secrets that are only accessible to the kernel. In an > ideal world this could be achieved by using TPM localities, but these > don't appear to be available on consumer systems. An alternative is to > simply block userland from modifying one of the resettable PCRs, leaving > it available to the kernel. If the kernel ensures that no userland can > access the TPM while it is carrying out work, it can reset PCR 23, > extend it to an arbitrary value, create or load a secret, and then reset > the PCR again. Even if userland somehow obtains the sealed material, it > will be unable to unseal it since PCR 23 will never be in the > appropriate state. > > From: Matthew Garrett <mjg59@xxxxxxxxxx> > Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx> > > Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx> Same issues as the other patch. > --- > Matthew's original version of this patch is at: > https://patchwork.kernel.org/patch/12096491/ Suggestion: find a lore URL instead for Matthew's patch, and then add "Link: <lore URL>" to your commit before sob's. It's a useful reference also in the commit log. > > Changes in v2: > - Fixed sparse warnings > > drivers/char/tpm/Kconfig | 10 +++++++++ > drivers/char/tpm/tpm-dev-common.c | 8 +++++++ > drivers/char/tpm/tpm.h | 21 +++++++++++++++++++ > drivers/char/tpm/tpm1-cmd.c | 35 +++++++++++++++++++++++++++++++ > drivers/char/tpm/tpm2-cmd.c | 22 +++++++++++++++++++ > drivers/char/tpm/tpm2-space.c | 2 +- > 6 files changed, 97 insertions(+), 1 deletion(-) > > diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig > index 927088b2c3d3f2..4483b61a428b11 100644 > --- a/drivers/char/tpm/Kconfig > +++ b/drivers/char/tpm/Kconfig > @@ -211,4 +211,14 @@ config TCG_FTPM_TEE > This driver proxies for firmware TPM running in TEE. > > source "drivers/char/tpm/st33zp24/Kconfig" > + > +config TCG_TPM_RESTRICT_PCR > + bool "Restrict userland access to PCR 23" > + depends on TCG_TPM > + help > + If set, block userland from extending or resetting PCR 23. This > + allows it to be restricted to in-kernel use, preventing userland > + from being able to make use of data sealed to the TPM by the kernel. > + This is required for secure hibernation support, but should be left > + disabled if any userland may require access to PCR23. > endif # TCG_TPM > diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c > index dc4c0a0a512903..7a4e618c7d1942 100644 > --- a/drivers/char/tpm/tpm-dev-common.c > +++ b/drivers/char/tpm/tpm-dev-common.c > @@ -198,6 +198,14 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf, > priv->response_read = false; > *off = 0; > > + if (priv->chip->flags & TPM_CHIP_FLAG_TPM2) > + ret = tpm2_cmd_restricted(priv->chip, priv->data_buffer, size); > + else > + ret = tpm1_cmd_restricted(priv->chip, priv->data_buffer, size); > + > + if (ret) > + goto out; > + > /* > * If in nonblocking mode schedule an async job to send > * the command return the size. > diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h > index a80b341d38eb8c..077c3ca0a127ba 100644 > --- a/drivers/char/tpm/tpm.h > +++ b/drivers/char/tpm/tpm.h > @@ -229,6 +229,8 @@ void tpm2_shutdown(struct tpm_chip *chip, u16 shutdown_type); > unsigned long tpm2_calc_ordinal_duration(struct tpm_chip *chip, u32 ordinal); > int tpm2_probe(struct tpm_chip *chip); > int tpm2_get_cc_attrs_tbl(struct tpm_chip *chip); > +int tpm_find_and_validate_cc(struct tpm_chip *chip, struct tpm_space *space, > + const void *buf, size_t bufsiz); > int tpm2_find_cc(struct tpm_chip *chip, u32 cc); > int tpm2_init_space(struct tpm_space *space, unsigned int buf_size); > void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space); > @@ -244,4 +246,23 @@ void tpm_bios_log_setup(struct tpm_chip *chip); > void tpm_bios_log_teardown(struct tpm_chip *chip); > int tpm_dev_common_init(void); > void tpm_dev_common_exit(void); > + > +#ifdef CONFIG_TCG_TPM_RESTRICT_PCR > +#define TPM_RESTRICTED_PCR 23 > + > +int tpm1_cmd_restricted(struct tpm_chip *chip, u8 *buffer, size_t size); > +int tpm2_cmd_restricted(struct tpm_chip *chip, u8 *buffer, size_t size); > +#else > +static inline int tpm1_cmd_restricted(struct tpm_chip *chip, u8 *buffer, > + size_t size) > +{ > + return 0; > +} > + > +static inline int tpm2_cmd_restricted(struct tpm_chip *chip, u8 *buffer, > + size_t size) > +{ > + return 0; > +} > +#endif > #endif > diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c > index 8ec743dec26544..318e75ae42fb85 100644 > --- a/drivers/char/tpm/tpm1-cmd.c > +++ b/drivers/char/tpm/tpm1-cmd.c > @@ -845,3 +845,38 @@ int tpm1_get_pcr_allocation(struct tpm_chip *chip) > > return 0; > } > + > +#ifdef CONFIG_TCG_TPM_RESTRICT_PCR > +int tpm1_cmd_restricted(struct tpm_chip *chip, u8 *buffer, size_t size) > +{ > + struct tpm_header *header = (struct tpm_header *)buffer; > + char len, offset; > + __be32 *pcr; > + int pos; > + > + switch (be32_to_cpu(header->ordinal)) { > + case TPM_ORD_PCR_EXTEND: > + if (size < (TPM_HEADER_SIZE + sizeof(u32))) > + return -EINVAL; > + pcr = (__be32 *)&buffer[TPM_HEADER_SIZE]; > + if (be32_to_cpu(*pcr) == TPM_RESTRICTED_PCR) > + return -EPERM; > + break; > + case TPM_ORD_PCR_RESET: > + if (size < (TPM_HEADER_SIZE + 1)) > + return -EINVAL; > + len = buffer[TPM_HEADER_SIZE]; > + if (size < (TPM_HEADER_SIZE + 1 + len)) > + return -EINVAL; > + offset = TPM_RESTRICTED_PCR/3; > + if (len < offset) > + break; > + pos = TPM_HEADER_SIZE + 1 + offset; > + if (buffer[pos] & (1 << (TPM_RESTRICTED_PCR - 2 * offset))) > + return -EPERM; > + break; > + } > + > + return 0; > +} > +#endif > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c > index 69126a6770386e..dbf7f5552c6782 100644 > --- a/drivers/char/tpm/tpm2-cmd.c > +++ b/drivers/char/tpm/tpm2-cmd.c > @@ -821,3 +821,25 @@ int tpm2_find_cc(struct tpm_chip *chip, u32 cc) > > return -1; > } > + > +#ifdef CONFIG_TCG_TPM_RESTRICT_PCR > +int tpm2_cmd_restricted(struct tpm_chip *chip, u8 *buffer, size_t size) > +{ > + int cc = tpm_find_and_validate_cc(chip, NULL, buffer, size); > + __be32 *handle; > + > + switch (cc) { > + case TPM2_CC_PCR_EXTEND: > + case TPM2_CC_PCR_RESET: > + if (size < (TPM_HEADER_SIZE + sizeof(u32))) > + return -EINVAL; > + > + handle = (__be32 *)&buffer[TPM_HEADER_SIZE]; > + if (be32_to_cpu(*handle) == TPM_RESTRICTED_PCR) > + return -EPERM; > + break; > + } > + > + return 0; > +} > +#endif > diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c > index ffb35f0154c16c..6f51cd92c6400f 100644 > --- a/drivers/char/tpm/tpm2-space.c > +++ b/drivers/char/tpm/tpm2-space.c > @@ -262,7 +262,7 @@ static int tpm2_map_command(struct tpm_chip *chip, u32 cc, u8 *cmd) > return 0; > } > > -static int tpm_find_and_validate_cc(struct tpm_chip *chip, > +int tpm_find_and_validate_cc(struct tpm_chip *chip, > struct tpm_space *space, > const void *cmd, size_t len) Split the export to a separate commit. > { > -- > 2.31.0 > BR, Jarkko
