Re: [PATCH 1/6] integrity: TPM internel kernel interface

[Rajiv Andrade]

On Tue, 2008-12-02 at 14:19 -0800, Dave Hansen wrote:
> On Tue, 2008-12-02 at 16:47 -0500, Mimi Zohar wrote:
> > This patch adds internal kernel support for:
> >   - reading/extending a pcr value
> >   - looking up the tpm_chip for a given chip number and type
> > 
> > Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Rajiv Andrade <srajiv@xxxxxxxxxx>
> > ---
> > diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
> > index 9c47dc4..17d2849 100644
> > --- a/drivers/char/tpm/tpm.c
> > +++ b/drivers/char/tpm/tpm.c
> > @@ -1,11 +1,12 @@
> >  /*
> > - * Copyright (C) 2004 IBM Corporation
> > + * Copyright (C) 2004,2007,2008 IBM Corporation
> >   *
> >   * Authors:
> >   * Leendert van Doorn <leendert@xxxxxxxxxxxxxx>
> >   * Dave Safford <safford@xxxxxxxxxxxxxx>
> >   * Reiner Sailer <sailer@xxxxxxxxxxxxxx>
> >   * Kylene Hall <kjhall@xxxxxxxxxx>
> > + * Debora Velarde <dvelarde@xxxxxxxxxx>
> >   *
> >   * Maintained by: <tpmdd-devel@xxxxxxxxxxxxxxxxxxxxx>
> >   *
> > @@ -28,6 +29,14 @@
> >  #include <linux/spinlock.h>
> >  #include <linux/smp_lock.h>
> >  
> > +#include <linux/mm.h>
> > +#include <linux/slab.h>
> > +#include <linux/string.h>
> > +#include <linux/crypto.h>
> > +#include <linux/fs.h>
> > +#include <linux/scatterlist.h>
> > +#include <linux/rcupdate.h>
> > +#include <asm/unaligned.h>
> >  #include "tpm.h"
> >  
> >  enum tpm_const {
> > @@ -50,6 +59,8 @@ enum tpm_duration {
> >  static LIST_HEAD(tpm_chip_list);
> >  static DEFINE_SPINLOCK(driver_lock);
> >  static DECLARE_BITMAP(dev_mask, TPM_NUM_DEVICES);
> > +#define TPM_CHIP_NUM_MASK       0x0000ffff
> > +#define TPM_CHIP_TYPE_SHIFT     16
> >  
> >  /*
> >   * Array with one entry per ordinal defining the maximum amount
> > @@ -366,8 +377,7 @@ EXPORT_SYMBOL_GPL(tpm_calc_ordinal_duration);
> >  /*
> >   * Internal kernel interface to transmit TPM commands
> >   */
> > -static ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
> > -			    size_t bufsiz)
> > +ssize_t tpm_transmit(struct tpm_chip *chip, char *buf, size_t bufsiz)
> >  {
> >  	ssize_t rc;
> >  	u32 count, ordinal;
> > @@ -425,6 +435,7 @@ out:
> >  	mutex_unlock(&chip->tpm_mutex);
> >  	return rc;
> >  }
> > +EXPORT_SYMBOL_GPL(tpm_transmit);
> >  
> >  #define TPM_DIGEST_SIZE 20
> >  #define TPM_ERROR_SIZE 10
> > @@ -717,6 +728,7 @@ ssize_t tpm_show_temp_deactivated(struct device * dev,
> >  }
> >  EXPORT_SYMBOL_GPL(tpm_show_temp_deactivated);
> >  
> > +#define READ_PCR_RESULT_SIZE 30
> >  static const u8 pcrread[] = {
> >  	0, 193,			/* TPM_TAG_RQU_COMMAND */
> >  	0, 0, 0, 14,		/* length */
> > @@ -772,6 +784,128 @@ out:
> >  }
> >  EXPORT_SYMBOL_GPL(tpm_show_pcrs);
> >  
> > +/*
> > + * tpm_chip_lookup - return tpm_chip for given chip number and type
> > + *
> > + * Must be called with rcu_read_lock.
> > + */
> > +static struct tpm_chip *tpm_chip_lookup(int chip_num, int chip_typ)
> > +{
> > +	struct tpm_chip *pos;
> > +	int rc;
> > +
> > +	list_for_each_entry_rcu(pos, &tpm_chip_list, list) {
> > +		rc = (chip_num == TPM_ANY_NUM || pos->dev_num == chip_num)
> > +		    && (chip_typ == TPM_ANY_TYPE);
> > +		if (rc)
> > +			return pos;
> > +	}
> > +	return NULL;
> > +}
> 
> If you have to respin these patches could you consider simplifying that
> loop?  I find that really hard to read.  I think it's much easier to
> read if written out something like this:
> 
> 	/* Dunno why they *must* specify TPM_ANY_TYPE, but they do */
> 	if (chip_typ != TPM_ANY_TYPE)
> 		continue;
> 
> 	if (chip_num == TPM_ANY_NUM)
> 		return pos;
> 	if (pos->dev_num == chip_num)
> 		return pos;
> 

If that's so confusing, it will be included in the next patchset.

> > +
> > +/**
> > + * tpm_pcr_read - read a pcr value
> > + * @chip_id: 	tpm chip identifier
> > + * 		Upper 2 bytes: ANY, HW_ONLY or SW_ONLY
> > + * 		Lower 2 bytes: tpm idx # or AN&
> > + * @pcr_idx:	pcr idx to retrieve
> > + * @res_buf: 	TPM_PCR value
> > + * 		size of res_buf is 20 bytes (or NULL if you don't care)
> > + *
> > + * The TPM driver should be built-in, but for whatever reason it
> > + * isn't, protect against the chip disappearing, by incrementing
> > + * the module usage count.
> > + */
> > +int tpm_pcr_read(u32 chip_id, int pcr_idx, u8 *res_buf)
> > +{
> > +	u8 data[READ_PCR_RESULT_SIZE];
> > +	int rc;
> > +	__be32 index;
> > +	int chip_num = chip_id & TPM_CHIP_NUM_MASK;
> > +	struct tpm_chip *chip;
> > +
> > +	rcu_read_lock();
> > +	chip = tpm_chip_lookup(chip_num, chip_id >> TPM_CHIP_TYPE_SHIFT);
> > +	if (chip == NULL) {
> > +		rcu_read_unlock();
> > +		return -ENODEV;
> > +	}
> > +	if (!try_module_get(chip->dev->driver->owner)) {
> > +		rcu_read_unlock();
> > +		return -ENODEV;
> > +	}
> > +	rcu_read_unlock();
> 
> This little bit of lookup, check for NULL, and try_module_get() looks
> cut-n-pasted in the next two functions.  Should be consolidated.
> 

Same here.

> Also, if you need to shift down the chip_id every time anyway, why not
> just do it inside the lookup function?

tpm_chip_lookup() only needs the chip type, not the entire chip_id, so
its usage is probably clearer if written this way.

> > +	BUILD_BUG_ON(sizeof(pcrread) > READ_PCR_RESULT_SIZE);
> > +	memcpy(data, pcrread, sizeof(pcrread));
> > +	index = cpu_to_be32(pcr_idx);
> > +	memcpy(data + 10, &index, 4);
> > +	rc = tpm_transmit(chip, data, sizeof(data));
> > +	if (rc > 0)
> > +		rc = get_unaligned_be32((__be32 *) (data + 6));
> > +
> > +	if (rc == 0 && res_buf)
> > +		memcpy(res_buf, data + 10, TPM_DIGEST_SIZE);
> > +
> > +	module_put(chip->dev->driver->owner);
> > +	return rc;
> > +}
> > +EXPORT_SYMBOL_GPL(tpm_pcr_read);
> > +
> > +#define EXTEND_PCR_SIZE 34
> > +static const u8 pcrextend[] = {
> > +	0, 193,			/* TPM_TAG_RQU_COMMAND */
> > +	0, 0, 0, 34,		/* length */
> > +	0, 0, 0, 20,		/* TPM_ORD_Extend */
> > +	0, 0, 0, 0		/* PCR index */
> > +};
> > +
> > +/**
> > + * tpm_pcr_extend - extend pcr value with hash
> > + * @chip_id: 	tpm chip identifier
> > + * 		Upper 2 bytes: ANY, HW_ONLY or SW_ONLY
> > + * 		Lower 2 bytes: tpm idx # or AN&
> > + * @pcr_idx:	pcr idx to extend
> > + * @hash: 	hash value used to extend pcr value
> > + *
> > + * The TPM driver should be built-in, but for whatever reason it
> > + * isn't, protect against the chip disappearing, by incrementing
> > + * the module usage count.
> > + */
> > +int tpm_pcr_extend(u32 chip_id, int pcr_idx, const u8 *hash)
> > +{
> > +	u8 data[EXTEND_PCR_SIZE];
> > +	int rc;
> > +	__be32 index;
> > +	int chip_num = chip_id & TPM_CHIP_NUM_MASK;
> > +	struct tpm_chip *chip;
> > +
> > +	rcu_read_lock();
> > +	chip = tpm_chip_lookup(chip_num, chip_id >> TPM_CHIP_TYPE_SHIFT);
> > +	if (chip == NULL) {
> > +		rcu_read_unlock();
> > +		return -ENODEV;
> > +	}
> > +	if (!try_module_get(chip->dev->driver->owner)) {
> > +		rcu_read_unlock();
> > +		return -ENODEV;
> > +	}
> > +	rcu_read_unlock();
> > +
> > +	BUILD_BUG_ON(sizeof(pcrextend) > EXTEND_PCR_SIZE);
> > +	memcpy(data, pcrextend, sizeof(pcrextend));
> > +	index = cpu_to_be32(pcr_idx);
> > +	memcpy(data + 10, &index, 4);
> 
> This bit of code looks duplicated too.  I really wish these 10's and
> 14's weren't magic numbers, especially since they're used twice.
> 

10 is pcrextend's size, and 14 is pcrextend's size + pcr_idx's size.
Probably this little math will be clearer by defining this values
previously, assigning a meaningful name to them..

> > +	memcpy(data + 14, hash, TPM_DIGEST_SIZE);
> > +	rc = tpm_transmit(chip, data, sizeof(data));
> > +	if (rc > 0)
> > +		rc = get_unaligned_be32((__be32 *) (data + 6));
> > +
> > +	module_put(chip->dev->driver->owner);
> > +	return rc;
> > +}
> 
> Looking at this, I can't help but think a couple of nicely laid out
> structs with a union or two could make this all look nicer.  For
> instance, is the return code from the tpm_transmit() function always
> returned in the 6th byte?
> 
> It looks to me like there is a TPM_RET_CODE_IDX in
> drivers/char/tpm/tpm.c.  Why on earth isn't that being used?  That also
> makes me question all these other magic numbers.
> 
It will be used, replacing the magical 6.

> Why not just integrate that rc tinkering into tpm_transmit(), or a
> variant of it.  There appear to be at least three or four other users
> that could benefit from such a function.  If you decide to mess with it
> further than just exporting it, please break that out into a separate
> patch, btw.
> 
> > +enum tpm_chip_num {
> > +	TPM_ANY_NUM = 0xFFFF,
> > +};
> 
> Why bother even checking this sucker if there's only one value?
> 
> > +#if defined(CONFIG_TCG_TPM) || defined(CONFIG_TCG_TPM_MODULE)
> > +
> > +extern int tpm_pcr_read(u32 chip_id, int pcr_idx, u8 *res_buf);
> > +extern int tpm_pcr_extend(u32 chip_id, int pcr_idx, const u8 *hash);
> > +#endif
> > +#endif
> 
> The " || defined(CONFIG_TCG_TPM_MODULE)" doesn't do anything.
> CONFIG_TCG_TPM is still true even when CONFIG_TCG_TPM_MODULE.
> 
> I also think so many authors on the header is a bit excessive.  5
> authors for 2 enums and 2 function declarations. :)
> 

We just added another 1, Debora Velarde, the new maintainer, and it's
for the whole tpm.c, not just this patch.

Thanks!

Rajiv

> -- Dave
> 
> --
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-- 
Rajiv Andrade <srajiv@xxxxxxxxxx>
Security Development
IBM Linux Technology Center


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