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Date: Tue, 02 Dec 2008 14:19:40 -0800
From: Dave Hansen <dave@...ux.vnet.ibm.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
James Morris <jmorris@...ei.org>,
Christoph Hellwig <hch@...radead.org>,
Al Viro <viro@...IV.linux.org.uk>,
David Safford <safford@...son.ibm.com>,
Serge Hallyn <serue@...ux.vnet.ibm.com>,
Rajiv Andrade <srajiv@...ibm.com>
Subject: Re: [PATCH 1/6] integrity: TPM internel kernel interface
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@...ux.vnet.ibm.com>
> Signed-off-by: Rajiv Andrade <srajiv@...ibm.com>
> ---
> 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@...son.ibm.com>
> * Dave Safford <safford@...son.ibm.com>
> * Reiner Sailer <sailer@...son.ibm.com>
> * Kylene Hall <kjhall@...ibm.com>
> + * Debora Velarde <dvelarde@...ibm.com>
> *
> * Maintained by: <tpmdd-devel@...ts.sourceforge.net>
> *
> @@ -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;
> +
> +/**
> + * 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.
Also, if you need to shift down the chip_id every time anyway, why not
just do it inside the lookup function?
> + 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.
> + 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.
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. :)
-- Dave
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