On Tue Sep 24, 2024 at 4:43 PM EEST, James Bottomley wrote: > On Sat, 2024-09-21 at 15:08 +0300, Jarkko Sakkinen wrote: > > Instead of flushing and reloading the auth session for every single > > transaction, keep the session open unless /dev/tpm0 is used. In > > practice this means applying TPM2_SA_CONTINUE_SESSION to the session > > attributes. Flush the session always when /dev/tpm0 is written. > > Patch looks fine but this description is way too terse to explain how > it works. > > I would suggest: > > Boot time elongation as a result of adding sessions has been reported > as an issue in https://bugzilla.kernel.org/show_bug.cgi?id=219229 > > The root cause is the addition of session overhead to > tpm2_pcr_extend(). This overhead can be reduced by not creating and > destroying a session for each invocation of the function. Do this by > keeping a session resident in the TPM for reuse by any session based > TPM command. The current flow of TPM commands in the kernel supports > this because tpm2_end_session() is only called for tpm errors because > most commands don't continue the session and expect the session to be > flushed on success. Thus we can add the continue session flag to > session creation to ensure the session won't be flushed except on > error, which is a rare case. > > Since the session consumes a slot in the TPM it must not be seen by > userspace but we can flush it whenever a command write occurs and re- > create it again on the next kernel session use. Since TPM use in boot > is somewhat rare this allows considerable reuse of the in-kernel > session and shortens boot time: > > <give figures> > > > > > > > Reported-by: Pengyu Ma <mapengyu@xxxxxxxxx> > > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219229 > > Cc: stable@xxxxxxxxxxxxxxx # v6.10+ > > Fixes: 7ca110f2679b ("tpm: Address !chip->auth in > > tpm_buf_append_hmac_session*()") > > Tested-by: Pengyu Ma <mapengyu@xxxxxxxxx> > > Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > > --- > > v5: > > - No changes. > > v4: > > - Changed as bug. > > v3: > > - Refined the commit message. > > - Removed the conditional for applying TPM2_SA_CONTINUE_SESSION only > > when > > /dev/tpm0 is open. It is not required as the auth session is > > flushed, > > not saved. > > v2: > > - A new patch. > > --- > > drivers/char/tpm/tpm-chip.c | 1 + > > drivers/char/tpm/tpm-dev-common.c | 1 + > > drivers/char/tpm/tpm-interface.c | 1 + > > drivers/char/tpm/tpm2-sessions.c | 3 +++ > > 4 files changed, 6 insertions(+) > > > > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm- > > chip.c > > index 0ea00e32f575..7a6bb30d1f32 100644 > > --- a/drivers/char/tpm/tpm-chip.c > > +++ b/drivers/char/tpm/tpm-chip.c > > @@ -680,6 +680,7 @@ void tpm_chip_unregister(struct tpm_chip *chip) > > rc = tpm_try_get_ops(chip); > > if (!rc) { > > if (chip->flags & TPM_CHIP_FLAG_TPM2) { > > + tpm2_end_auth_session(chip); > > tpm2_flush_context(chip, chip->null_key); > > chip->null_key = 0; > > } > > diff --git a/drivers/char/tpm/tpm-dev-common.c > > b/drivers/char/tpm/tpm-dev-common.c > > index 4eaa8e05c291..a3ed7a99a394 100644 > > --- a/drivers/char/tpm/tpm-dev-common.c > > +++ b/drivers/char/tpm/tpm-dev-common.c > > @@ -29,6 +29,7 @@ static ssize_t tpm_dev_transmit(struct tpm_chip > > *chip, struct tpm_space *space, > > > > #ifdef CONFIG_TCG_TPM2_HMAC > > if (chip->flags & TPM_CHIP_FLAG_TPM2) { > > + tpm2_end_auth_session(chip); > > tpm2_flush_context(chip, chip->null_key); > > chip->null_key = 0; > > } > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm- > > interface.c > > index bfa47d48b0f2..2363018fa8fb 100644 > > --- a/drivers/char/tpm/tpm-interface.c > > +++ b/drivers/char/tpm/tpm-interface.c > > @@ -381,6 +381,7 @@ int tpm_pm_suspend(struct device *dev) > > if (!rc) { > > if (chip->flags & TPM_CHIP_FLAG_TPM2) { > > #ifdef CONFIG_TCG_TPM2_HMAC > > + tpm2_end_auth_session(chip); > > tpm2_flush_context(chip, chip->null_key); > > chip->null_key = 0; > > #endif > > diff --git a/drivers/char/tpm/tpm2-sessions.c > > b/drivers/char/tpm/tpm2-sessions.c > > index a8d3d5d52178..38b92ad9e75f 100644 > > --- a/drivers/char/tpm/tpm2-sessions.c > > +++ b/drivers/char/tpm/tpm2-sessions.c > > @@ -333,6 +333,9 @@ void tpm_buf_append_hmac_session(struct tpm_chip > > *chip, struct tpm_buf *buf, > > } > > > > #ifdef CONFIG_TCG_TPM2_HMAC > > + /* The first write to /dev/tpm{rm0} will flush the session. > > */ > > + attributes |= TPM2_SA_CONTINUE_SESSION; > > + > > /* > > * The Architecture Guide requires us to strip trailing zeros > > * before computing the HMAC > > Code is fine, with the change log update, you can add > > Reviewed-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> OK, thank you. BR, Jarkko
