On Mon, Sep 15, 2025 at 2:39 PM Jarkko Sakkinen <[email protected]> wrote: > > On Tue, Sep 02, 2025 at 10:24:30AM -0400, Denis Aleksandrov wrote: > > Reads on tpm/tpm0/ppi/*operations can become very long on > > misconfigured systems. Reading the TPM is a blocking operation, > > thus a user could effectively trigger a DOS. > > > > Resolve this by caching the results and avoiding the blocking > > operations after the first read. > > > > Reported-by: Jan Stancek <[email protected]> > > Signed-off-by: Denis Aleksandrov <[email protected]> > > Suggested-by: Jarkko Sakkinen <[email protected]> > > Reviewed-by: Paul Menzel <[email protected]> > > --- > > > > Changes in v4: > > - Removes empty lines. > > - Reorders vars to reverse christmas tree. > > > > drivers/char/tpm/tpm_ppi.c | 85 +++++++++++++++++++++++++++----------- > > 1 file changed, 62 insertions(+), 23 deletions(-) > > > > diff --git a/drivers/char/tpm/tpm_ppi.c b/drivers/char/tpm/tpm_ppi.c > > index d53fce1c9d6f..df34b215440d 100644 > > --- a/drivers/char/tpm/tpm_ppi.c > > +++ b/drivers/char/tpm/tpm_ppi.c > > @@ -33,6 +33,20 @@ static const guid_t tpm_ppi_guid = > > GUID_INIT(0x3DDDFAA6, 0x361B, 0x4EB4, > > 0xA4, 0x24, 0x8D, 0x10, 0x08, 0x9D, 0x16, 0x53); > > > > +static const char * const tpm_ppi_info[] = { > > + "Not implemented", > > + "BIOS only", > > + "Blocked for OS by system firmware", > > + "User required", > > + "User not required", > > +}; > > + > > +/* A spinlock to protect access to the cache from concurrent reads */ > > +static DEFINE_SPINLOCK(tpm_ppi_lock); > > + > > +static u32 ppi_operations_cache[PPI_VS_REQ_END + 1]; > > +static bool ppi_cache_populated; > > + > > static bool tpm_ppi_req_has_parameter(u64 req) > > { > > return req == 23; > > @@ -277,8 +291,7 @@ static ssize_t tpm_show_ppi_response(struct device *dev, > > return status; > > } > > > > -static ssize_t show_ppi_operations(acpi_handle dev_handle, char *buf, u32 > > start, > > - u32 end) > > +static ssize_t cache_ppi_operations(acpi_handle dev_handle, char *buf) > > { > > int i; > > u32 ret; > > @@ -286,34 +299,22 @@ static ssize_t show_ppi_operations(acpi_handle > > dev_handle, char *buf, u32 start, > > union acpi_object *obj, tmp; > > union acpi_object argv = ACPI_INIT_DSM_ARGV4(1, &tmp); > > > > - static char *info[] = { > > - "Not implemented", > > - "BIOS only", > > - "Blocked for OS by BIOS", > > - "User required", > > - "User not required", > > - }; > > - > > if (!acpi_check_dsm(dev_handle, &tpm_ppi_guid, TPM_PPI_REVISION_ID_1, > > 1 << TPM_PPI_FN_GETOPR)) > > return -EPERM; > > > > tmp.integer.type = ACPI_TYPE_INTEGER; > > - for (i = start; i <= end; i++) { > > + for (i = 0; i <= PPI_VS_REQ_END; i++) { > > tmp.integer.value = i; > > obj = tpm_eval_dsm(dev_handle, TPM_PPI_FN_GETOPR, > > ACPI_TYPE_INTEGER, &argv, > > TPM_PPI_REVISION_ID_1); > > - if (!obj) { > > + if (!obj) > > return -ENOMEM; > > - } else { > > - ret = obj->integer.value; > > - ACPI_FREE(obj); > > - } > > > > - if (ret > 0 && ret < ARRAY_SIZE(info)) > > - len += sysfs_emit_at(buf, len, "%d %d: %s\n", > > - i, ret, info[ret]); > > + ret = obj->integer.value; > > + ppi_operations_cache[i] = ret; > > + ACPI_FREE(obj); > > } > > > > return len; > > @@ -324,9 +325,28 @@ static ssize_t tpm_show_ppi_tcg_operations(struct > > device *dev, > > char *buf) > > { > > struct tpm_chip *chip = to_tpm_chip(dev); > > + ssize_t len = 0; > > + u32 ret; > > + int i; > > + > > + spin_lock(&tpm_ppi_lock); > > + if (!ppi_cache_populated) { > > + len = cache_ppi_operations(chip->acpi_dev_handle, buf); > > + if (len < 0) > > + return len; > > > > - return show_ppi_operations(chip->acpi_dev_handle, buf, 0, > > - PPI_TPM_REQ_MAX); > > + ppi_cache_populated = true; > > + } > > + > > + for (i = 0; i <= PPI_TPM_REQ_MAX; i++) { > > + ret = ppi_operations_cache[i]; > > + if (ret >= 0 && ret < ARRAY_SIZE(tpm_ppi_info)) > > + len += sysfs_emit_at(buf, len, "%d %d: %s\n", > > + i, ret, > > tpm_ppi_info[ret]); > > + } > > + spin_unlock(&tpm_ppi_lock); > > + > > + return len; > > } > > > > static ssize_t tpm_show_ppi_vs_operations(struct device *dev, > > @@ -334,9 +354,28 @@ static ssize_t tpm_show_ppi_vs_operations(struct > > device *dev, > > char *buf) > > { > > struct tpm_chip *chip = to_tpm_chip(dev); > > + ssize_t len = 0; > > + u32 ret; > > + int i; > > > > - return show_ppi_operations(chip->acpi_dev_handle, buf, > > PPI_VS_REQ_START, > > - PPI_VS_REQ_END); > > + spin_lock(&tpm_ppi_lock); > > + if (!ppi_cache_populated) { > > + len = cache_ppi_operations(chip->acpi_dev_handle, buf); > > + if (len < 0) > > + return len; > > + > > + ppi_cache_populated = true; > > + } > > + > > + for (i = PPI_VS_REQ_START; i <= PPI_VS_REQ_END; i++) { > > + ret = ppi_operations_cache[i]; > > + if (ret >= 0 && ret < ARRAY_SIZE(tpm_ppi_info)) > > + len += sysfs_emit_at(buf, len, "%d %d: %s\n", > > + i, ret, > > tpm_ppi_info[ret]); > > + } > > + spin_unlock(&tpm_ppi_lock); > > + > > + return len; > > } > > > > static DEVICE_ATTR(version, S_IRUGO, tpm_show_ppi_version, NULL); > > -- > > 2.48.1 > > > > I don't know how I messed up the patch in my Git but now it is good > (I think): > > https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/commit/?h=next > > Please check before I move forward with the PR.
The commit looks good, besides my mistake of not freeing the lock upon an error. I was just curious if we should follow Paul's recommendation about separating the previously mentioned changes into another patch. I'm okay with moving forward with the current changes without breaking it up into another patch. I'll send over a v5 shortly. The only changes I will introduce to the existing patch is proper lock management. > > BR, Jarkko > Thanks, Denis
