Messages in this thread | | | Date | Wed, 24 May 2017 10:35:21 -0700 | From | Jarkko Sakkinen <> | Subject | Re: [PATCH v2 1/5] tpm: introduce tpm_pcr_algorithms() |
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On Mon, May 22, 2017 at 11:07:54AM +0200, Roberto Sassu wrote: > On 5/20/2017 3:18 PM, Jarkko Sakkinen wrote: > > On Wed, May 17, 2017 at 10:42:35AM +0200, Roberto Sassu wrote: > > > On 5/15/2017 3:18 PM, Roberto Sassu wrote: > > > > > > > > > > > > On 5/15/2017 12:36 PM, Jarkko Sakkinen wrote: > > > > > On Fri, May 05, 2017 at 04:21:48PM +0200, Roberto Sassu wrote: > > > > > > This function allows TPM users to know which algorithms the TPM > > > > > > supports. > > > > > > It stores the algorithms in a static array of 'enum tpm2_algorithms', > > > > > > allocated by the caller. If the array is not large enough, the function > > > > > > returns an error. Otherwise, it returns the number of algorithms written > > > > > > to the array. If the TPM version is 1.2, the function writes > > > > > > TPM2_ALG_SHA1 > > > > > > to first element of the array. > > > > > > > > > > > > Writing the algorithm also for TPM 1.2 has the advantage that callers > > > > > > can use the API, tpm_pcr_algorithms() and tpm_pcr_extend(), regardless > > > > > > of the TPM version. > > > > > > > > > > > > A minor change added to this patch was to make available the size of > > > > > > the active_banks array, member of the tpm_chip structure, outside > > > > > > the TPM driver. The array size (TPM_ACTIVE_BANKS_MAX) has been exported > > > > > > to include/linux/tpm.h. > > > > > > > > > > > > With this information, callers of tpm_pcr_algorithms() can provide > > > > > > a static array with enough room for all the algorithms, instead > > > > > > of receiving the pointer of a dynamic array that they have to free > > > > > > later. > > > > > > > > > > > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > > > > > > --- > > > > > > v2 > > > > > > > > > > > > - tpm_pcr_algorithms() returns supported algorithms also for TPM 1.2 > > > > > > > > > > > > drivers/char/tpm/tpm-interface.c | 46 > > > > > > ++++++++++++++++++++++++++++++++++++++++ > > > > > > drivers/char/tpm/tpm.h | 13 +----------- > > > > > > include/linux/tpm.h | 19 +++++++++++++++++ > > > > > > 3 files changed, 66 insertions(+), 12 deletions(-) > > > > > > > > > > > > diff --git a/drivers/char/tpm/tpm-interface.c > > > > > > b/drivers/char/tpm/tpm-interface.c > > > > > > index 4ed08ab..b90de3d 100644 > > > > > > --- a/drivers/char/tpm/tpm-interface.c > > > > > > +++ b/drivers/char/tpm/tpm-interface.c > > > > > > @@ -911,6 +911,52 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx, > > > > > > const u8 *hash) > > > > > > EXPORT_SYMBOL_GPL(tpm_pcr_extend); > > > > > > > > > > > > /** > > > > > > + * tpm_pcr_algorithms - get TPM IDs of active PCR banks algorithms > > > > > > > > > > The grammar is incorrect here I believe. Should rather be > > > > > > > > > > "algorithms of the active PCR banks" > > > > > > > > > > And there is no such thing as "TPM ID". > > > > > > > > > > > + * @chip_num: tpm idx # or ANY > > > > > > + * @count: # of items in algorithms > > > > > > + * @algorithms: array of TPM IDs > > > > > > + * > > > > > > + * Returns < 0 on error, and the number of active PCR banks on success. > > > > > > + * > > > > > > + * TPM 1.2 has always one SHA1 bank. > > > > > > + */ > > > > > > +int tpm_pcr_algorithms(u32 chip_num, int count, > > > > > > + enum tpm2_algorithms *algorithms) > > > > > unsigned int > > > > > > > > > > In addition the function name is not too greatg, > > > > > > > > > > Your syntax for return value is not correct. In addition after > > > > > describing the return value there should not be anything. You should > > > > > study > > > > > > > > > > https://www.kernel.org/doc/Documentation/kernel-doc-nano-HOWTO.txt > > > > > > > > > > Better name for the function would be tpm_get_pcr_algorithms(). > > > > > > > > > > > +{ > > > > > > + struct tpm_chip *chip; > > > > > > + int i; > > > > > > + > > > > > > + if (count <= 0 || algorithms == NULL) > > > > > > + return -EINVAL; > > > > > > > > > > Is there a legal case where caller would pass these values? Now it > > > > > looks like that there is. > > > > > > > > > > 'count' should unsigned int and zero should be a legal value for > > > > > count. > > > > > > > > I wanted to avoid that a negative value returned by tpm_pcr_algorithms() > > > > is passed to tpm_pcr_extend() as unsigned int. > > > > > > > > > > > > > That said I think the whole design is wrong as you could calculate > > > > > array for algs only one time and pass a const reference to it on > > > > > request. > > > > > > > > Ok. If I understood it correctly, you are saying to pass a const > > > > reference of chip->active_banks. Then, I should also: > > > > > > This is not a viable option. chip could be freed and the reference > > > becomes invalid, without increasing the reference count. > > > > > > Did you think about something different? > > > > > > Thanks > > > > > > Roberto > > > > Two alternatives come in mind. > > > > 1. add tpm_put to linclude/linux/tpm.h > > 2. take put_ops away from the implementation > > 3. add documentation that tpm_put needs to be called > > > > or acceptable alternative would memcpy in the implementation > > > > In any case, you should probably drop completely 'count' and have > > function for getting the number of active banks. > > Having a variable number, makes things more complicated. > In the IMA patch set for multiple template digests, > the array of algorithms is stored inside a structure > called digest descriptor. The array size must be fixed, > to avoid VLAIS (which is not supported by clang).
What is VLAI?
You can always allocate it from heap.
> Since the size of tpm_chip->active_banks is a small number, > we can drop count, and assume that the size of the array > passed to tpm_pcr_algorithms() always matches the size > of the active_banks array. > > Roberto
I don't understand what you mean.
/Jarkko
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