Message-ID: <e725bea0-e2d0-47ce-9128-5187cefecff7@intel.com>
Date: Wed, 19 Feb 2025 19:01:14 -0600
From: "Xing, Cedric" <cedric.xing@...el.com>
To: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>, <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH 1/4] tsm: Add TVM Measurement Register support

On 2/17/2025 7:10 PM, Sathyanarayanan Kuppuswamy wrote:
> Hi Cedric,
> 
> On 2/12/25 6:23 PM, Cedric Xing wrote:
>> This commit extends the TSM core with support for CC measurement 
>> registers
>> (MRs).
>>
>> The newly added APIs are:
>>
>> - `tsm_register_measurement(struct tsm_measurement *)`: This API allows a
>>    CC guest driver to register a set of measurement registers with the 
>> TSM
>>    core.
>> - `tsm_unregister_measurement(struct tsm_measurement *)`: This API 
>> enables
>>    a CC guest driver to unregister a previously registered set of
>>    measurement registers.
>>
>> `struct tsm_measurement` has been defined to encapsulate the details of
>> CC-specific MRs. It includes an array of `struct 
>> tsm_measurement_register`s
>> and provides operations for reading and updating these registers. For a
>> comprehensive understanding of the structure and its usage, refer to the
>> detailed comments in `include/linux/tsm.h`.
>>
>> Upon successful registration of a measurement provider, the TSM core
>> exposes the MRs through a directory tree in the sysfs filesystem. The 
>> root
>> of this tree is located at `/sys/kernel/tsm/MR_PROVIDER/`, where
>> `MR_PROVIDER` is the name of the measurement provider (as specified by
>> `struct tsm_measurement::name`). Each MR is made accessible as either a
>> file or a directory of the specified name (i.e.,
>> `tsm_measurement_register::mr_name`). In the former case, the file 
>> content
> 
> May be include some info on when a MR can be just a file (like an example)
> 
Will do.

>> is the MR value; while in the latter case `HASH_ALG/digest` under the MR
>> directory contains the MR value, where `HASH_ALG` specifies the hash
>> algorithm (e.g., sha256, sha384, etc.) used by this MR.
>>
>> *Crypto Agility* is supported as a set of independent MRs that share a
>> common name. These MRs will be merged into a single MR directory and each
>> will be represented by its respective `HASH_ALG/digest` file. Note that
>> `tsm_measurement_register::mr_hash` must be distinct or the behavior is
>> undefined.
> 
> is this required/supported in any of the existing CC providers?
> 
> By sharing a common name, you mean internally there will be distinct
> registers for every crypto algo supported?
> 
This is explicitly requested by James Bottomley. And yes, an MR with >1 
algo is in fact a collection of independent MRs, even though they are 
referred to as the "banks" of the same MR in TCG/TPM spec.

>>
>> Signed-off-by: Cedric Xing <cedric.xing@...el.com>
>> ---
>>   Documentation/ABI/testing/sysfs-kernel-tsm |  20 ++
>>   MAINTAINERS                                |   2 +-
>>   drivers/virt/coco/Kconfig                  |   3 +-
>>   drivers/virt/coco/Makefile                 |   2 +
>>   drivers/virt/coco/{tsm.c => tsm-core.c}    |   6 +-
>>   drivers/virt/coco/tsm-mr.c                 | 375 +++++++++++++++++++ 
>> ++++++++++
>>   include/linux/tsm.h                        |  64 +++++
>>   7 files changed, 469 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-kernel-tsm b/ 
>> Documentation/ABI/testing/sysfs-kernel-tsm
>> new file mode 100644
>> index 000000000000..99735cf4da5c
>> --- /dev/null
>> +++ b/Documentation/ABI/testing/sysfs-kernel-tsm
>> @@ -0,0 +1,20 @@
>> +What:        /sys/kernel/tsm/<measurement_provider>/<register>
> 
> Any reason for not using fixed name for registers (like mr[0-n])? May be it
> will help if user space use a generic code across vendors.
> 
The names of MRs identify the hardware resources, while the semantics of 
an MR (e.g., whose measurements it contains) is defined by applications. 
A good design should separate those two to allow applications to connect 
them as needed. For example, say all loadable modules must be measured 
before being loaded, and shall be measured/extended to rtmrX on arch A 
and to rtmrY on arch B, respectively. A portable implementation could 
always extend to "rtmrModule", which would be a symlink pointing to 
either rtmrX or rtmrY depending on the underlying arch. On the contrary, 
extending to the same mr[z] is equivalent to forcing z == X == Y, which 
_breaks_ portability as different archs tend to have different number of 
RTMRs.

One more thing worth noting here is: different archs may choose 
different hash algorithms for RTMRs, and that forces applications to be 
arch aware. The solution will be a "log centric" ABI that we don't have yet.

>> +Date:        February 2025
>> +Contact:    Cedric Xing <cedric.xing@...el.com>.
>> +Description:
>> +        This file contains the value of the measurement register
>> +        <register>. Depending on the CC architecture, this file may be
>> +        writable, in which case the value written will be the new value
>> +        of <register>. Each write must start at the beginning and be of
>> +        the same size as the file. Partial writes are not permitted.
>> +
>> +What:        /sys/kernel/tsm/<measurement_provider>/<register>/ 
>> <hash>/digest
>> +Date:        February 2025
>> +Contact:    Cedric Xing <cedric.xing@...el.com>.
>> +Description:
>> +        This file contains the value of the measurement register
>> +        <register>. Depending on the CC architecture, this file may be
>> +        writable, in which case any value written may be extended to
>> +        <register> using <hash>. Each write must start at the beginning
>> +        and be of the same size as the file. Partial writes are not
>> +        permitted.
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 25c86f47353d..c129fccd3d5a 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -24098,7 +24098,7 @@ M:    Dan Williams <dan.j.williams@...el.com>
>>   L:    linux-coco@...ts.linux.dev
>>   S:    Maintained
>>   F:    Documentation/ABI/testing/configfs-tsm
>> -F:    drivers/virt/coco/tsm.c
>> +F:    drivers/virt/coco/tsm*.c
>>   F:    include/linux/tsm.h
>>   TRUSTED SERVICES TEE DRIVER
>> diff --git a/drivers/virt/coco/Kconfig b/drivers/virt/coco/Kconfig
>> index ff869d883d95..6f3c0831680b 100644
>> --- a/drivers/virt/coco/Kconfig
>> +++ b/drivers/virt/coco/Kconfig
>> @@ -5,7 +5,8 @@
>>   config TSM_REPORTS
>>       select CONFIGFS_FS
>> -    tristate
>> +    select CRYPTO_HASH_INFO
>> +    tristate "Trusted Security Module (TSM) sysfs/configfs support"
> 
> IMO, sysfs/configfs part is not required in the title.
> 
Ok. I'll take it out.

>>   source "drivers/virt/coco/efi_secret/Kconfig"
>> diff --git a/drivers/virt/coco/Makefile b/drivers/virt/coco/Makefile
>> index c3d07cfc087e..4b108d8df1bd 100644
>> --- a/drivers/virt/coco/Makefile
>> +++ b/drivers/virt/coco/Makefile
>> @@ -2,6 +2,8 @@
>>   #
>>   # Confidential computing related collateral
>>   #
>> +tsm-y                += tsm-core.o tsm-mr.o
>> +
>>   obj-$(CONFIG_TSM_REPORTS)    += tsm.o
>>   obj-$(CONFIG_EFI_SECRET)    += efi_secret/
>>   obj-$(CONFIG_ARM_PKVM_GUEST)    += pkvm-guest/
>> diff --git a/drivers/virt/coco/tsm.c b/drivers/virt/coco/tsm-core.c
>> similarity index 99%
>> rename from drivers/virt/coco/tsm.c
>> rename to drivers/virt/coco/tsm-core.c
>> index 9432d4e303f1..ab5269db9c13 100644
>> --- a/drivers/virt/coco/tsm.c
>> +++ b/drivers/virt/coco/tsm-core.c
>> @@ -476,6 +476,9 @@ int tsm_unregister(const struct tsm_ops *ops)
>>   }
>>   EXPORT_SYMBOL_GPL(tsm_unregister);
>> +int tsm_mr_init(void);
>> +void tsm_mr_exit(void);
>> +
>>   static struct config_group *tsm_report_group;
>>   static int __init tsm_init(void)
>> @@ -497,12 +500,13 @@ static int __init tsm_init(void)
>>       }
>>       tsm_report_group = tsm;
>> -    return 0;
>> +    return tsm_mr_init();
>>   }
>>   module_init(tsm_init);
>>   static void __exit tsm_exit(void)
>>   {
>> +    tsm_mr_exit();
>>       configfs_unregister_default_group(tsm_report_group);
>>       configfs_unregister_subsystem(&tsm_configfs);
>>   }
>> diff --git a/drivers/virt/coco/tsm-mr.c b/drivers/virt/coco/tsm-mr.c
>> new file mode 100644
>> index 000000000000..8d26e952da6b
>> --- /dev/null
>> +++ b/drivers/virt/coco/tsm-mr.c
>> @@ -0,0 +1,375 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/* Copyright(c) 2024-2025 Intel Corporation. All rights reserved. */
>> +
>> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>> +
>> +#include <crypto/hash.h>
>> +#include <crypto/hash_info.h>
>> +#include <linux/kobject.h>
>> +#include <linux/module.h>
>> +#include <linux/tsm.h>
>> +
>> +int tsm_mr_init(void);
>> +void tsm_mr_exit(void);
>> +
>> +enum tmr_dir_battr_index {
>> +    TMR_DIR_BA_DIGEST,
>> +    TMR_DIR_BA__COUNT,
> 
> Why not use single underscore uniformly?
> 
DIGEST is a bin attribute while _COUNT is the _count_ of bin attributes. 
If w/o the underscore, COUNT would look like another bin attribute.

>> +
>> +    TMR_DIR__ALGO_MAX = 4,
> 
> Since this is not related to attribute index, why not use #define?
> 
Now I'm thinking of making it a CONFIG option, default to 4.

>> +};
>> +
>> +struct tmr_dir {
>> +    struct kobject kobj;
>> +    struct bin_attribute battrs[TMR_DIR__ALGO_MAX][TMR_DIR_BA__COUNT];
>> +    int algo;
>> +};
>> +
>> +struct tmr_provider {
>> +    struct kset kset;
>> +    struct rw_semaphore rwsem;
>> +    struct bin_attribute *mrfiles;
>> +    struct tsm_measurement *tmr;
>> +    bool in_sync;
>> +};
>> +
>> +static inline struct tmr_provider *tmr_mr_to_provider(const struct 
>> tsm_measurement_register *mr,
>> +                              struct kobject *kobj)
>> +{
>> +    if (mr->mr_flags & TSM_MR_F_F)
>> +        return container_of(kobj, struct tmr_provider, kset.kobj);
>> +    else
>> +        return container_of(kobj->kset, struct tmr_provider, kset);
>> +}
>> +
>> +static inline int tmr_call_refresh(struct tmr_provider *pvd,
>> +                   const struct tsm_measurement_register *mr)
>> +{
>> +    int rc;
>> +
>> +    rc = pvd->tmr->refresh(pvd->tmr, mr);
>> +    if (rc)
>> +        pr_warn("%s.refresh(%s) failed %d\n", kobject_name(&pvd- 
>> >kset.kobj), mr->mr_name,
>> +            rc);
>> +    return rc;
>> +}
>> +
>> +static inline int tmr_call_extend(struct tmr_provider *pvd,
>> +                  const struct tsm_measurement_register *mr, const u8 
>> *data)
>> +{
>> +    int rc;
>> +
>> +    rc = pvd->tmr->extend(pvd->tmr, mr, data);
>> +    if (rc)
>> +        pr_warn("%s.extend(%s) failed %d\n", kobject_name(&pvd- 
>> >kset.kobj), mr->mr_name,
>> +            rc);
>> +    return rc;
>> +}
>> +
>> +static ssize_t tmr_digest_read(struct file *filp, struct kobject 
>> *kobj, struct bin_attribute *attr,
>> +                   char *page, loff_t off, size_t count)
>> +{
>> +    const struct tsm_measurement_register *mr;
>> +    struct tmr_provider *pvd;
>> +    int rc;
>> +
>> +    if (off < 0 || off > attr->size)
>> +        return -EINVAL;
>> +
>> +    count = min(count, attr->size - (size_t)off);
>> +    if (!count)
>> +        return count;
>> +
>> +    mr = (typeof(mr))attr->private;
> 
> I think you don't need to cast it.
> 
Thanks! I'll remove it.

>> +    pvd = tmr_mr_to_provider(mr, kobj);
>> +    rc = down_read_interruptible(&pvd->rwsem);
>> +    if (rc)
>> +        return rc;
>> +
>> +    if ((mr->mr_flags & TSM_MR_F_L) && !pvd->in_sync) {
>> +        up_read(&pvd->rwsem);
>> +
>> +        rc = down_write_killable(&pvd->rwsem);
>> +        if (rc)
>> +            return rc;
>> +
>> +        if (!pvd->in_sync) {
> 
> Since this path is only taken if in_sync is false, do you need to check 
> again?
> 
Yes, because in_sync could be set to true between up_read and 
down_write_killable above.

>> +            rc = tmr_call_refresh(pvd, mr);
>> +            pvd->in_sync = !rc;
>> +        }
>> +
>> +        downgrade_write(&pvd->rwsem);
>> +    }
>> +
>> +    if (!rc)
>> +        memcpy(page, mr->mr_value + off, count);
>> +
>> +    up_read(&pvd->rwsem);
>> +    return rc ?: count;
>> +}
>> +
>> +static ssize_t tmr_digest_write(struct file *filp, struct kobject 
>> *kobj, struct bin_attribute *attr,
>> +                char *page, loff_t off, size_t count)
>> +{
>> +    const struct tsm_measurement_register *mr;
>> +    struct tmr_provider *pvd;
>> +    ssize_t rc;
>> +
>> +    if (off != 0 || count != attr->size)
>> +        return -EINVAL;
>> +
>> +    mr = (typeof(mr))attr->private;
>> +    pvd = tmr_mr_to_provider(mr, kobj);
>> +    rc = down_write_killable(&pvd->rwsem);
>> +    if (rc)
>> +        return rc;
>> +
>> +    if (mr->mr_flags & TSM_MR_F_X)
>> +        rc = tmr_call_extend(pvd, mr, page);
>> +    else
>> +        memcpy(mr->mr_value, page, count);
>> +
>> +    if (!rc)
>> +        pvd->in_sync = false;
>> +
>> +    up_write(&pvd->rwsem);
>> +    return rc ?: count;
>> +}
>> +
>> +static void tmr_dir_release(struct kobject *kobj)
>> +{
>> +    struct tmr_dir *mrd;
>> +
>> +    mrd = container_of(kobj, typeof(*mrd), kobj);
>> +    kfree(mrd);
>> +}
>> +
>> +static const struct kobj_type tmr_dir_ktype = {
>> +    .release = tmr_dir_release,
>> +    .sysfs_ops = &kobj_sysfs_ops,
>> +};
>> +
>> +static struct tmr_dir *tmr_dir_create(const struct 
>> tsm_measurement_register *mr,
>> +                      struct tmr_provider *pvd)
>> +{
>> +    struct kobject *kobj;
>> +    struct tmr_dir *mrd;
>> +
>> +    kobj = kset_find_obj(&pvd->kset, mr->mr_name);
>> +    if (kobj) {
>> +        mrd = container_of(kobj, typeof(*mrd), kobj);
>> +        kobject_put(kobj);
>> +        if (++mrd->algo >= TMR_DIR__ALGO_MAX) {
>> +            --mrd->algo;
>> +            return ERR_PTR(-ENOSPC);
>> +        }
>> +    } else {
>> +        int rc;
>> +
>> +        mrd = kzalloc(sizeof(*mrd), GFP_KERNEL);
>> +        if (!mrd)
>> +            return ERR_PTR(-ENOMEM);
>> +
>> +        mrd->kobj.kset = &pvd->kset;
>> +        rc = kobject_init_and_add(&mrd->kobj, &tmr_dir_ktype, NULL, 
>> "%s", mr->mr_name);
>> +        if (rc) {
>> +            kfree(mrd);
>> +            return ERR_PTR(rc);
>> +        }
>> +    }
>> +
>> +    sysfs_bin_attr_init(&mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST]);
>> +    mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].attr.name = "digest";
> 
> Since this attribute reflects register value, personally I think "value" 
> is more clear
> than "digest". But it is fine either way.
> 
This attribute shows up only when its parent dir is a hash algo name 
(e.g., "sha384"). So "digest" I believe is more appropriate to refer to 
the result of the hash.

>> +    if (mr->mr_flags & TSM_MR_F_W)
>> +        mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].attr.mode |= 
>> S_IWUSR | S_IWGRP;
>> +    if (mr->mr_flags & TSM_MR_F_R)
>> +        mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].attr.mode |= S_IRUGO;
>> +
>> +    mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].size = mr->mr_size;
>> +    mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].read = tmr_digest_read;
>> +    mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].write = tmr_digest_write;
>> +    mrd->battrs[mrd->algo][TMR_DIR_BA_DIGEST].private = (void *)mr;
>> +
>> +    return mrd;
>> +}
>> +
>> +static void tmr_provider_release(struct kobject *kobj)
>> +{
>> +    struct tmr_provider *pvd;
>> +
>> +    pvd = container_of(kobj, typeof(*pvd), kset.kobj);
>> +    if (!WARN_ON(!list_empty(&pvd->kset.list))) {
>> +        kfree(pvd->mrfiles);
>> +        kfree(pvd);
>> +    }
>> +}
>> +
>> +static const struct kobj_type _mr_provider_ktype = {
>> +    .release = tmr_provider_release,
>> +    .sysfs_ops = &kobj_sysfs_ops,
>> +};
>> +
>> +static struct kset *tmr_sysfs_root;
>> +
>> +static struct tmr_provider *tmr_provider_create(struct 
>> tsm_measurement *tmr)
>> +{
>> +    struct tmr_provider *pvd __free(kfree);
>> +    int rc;
>> +
>> +    pvd = kzalloc(sizeof(*pvd), GFP_KERNEL);
>> +    if (!pvd)
>> +        return ERR_PTR(-ENOMEM);
>> +
>> +    if (!tmr->name || !tmr->mrs || !tmr->refresh || !tmr->extend)
>> +        return ERR_PTR(-EINVAL);
> 
> Why not add this condition at the top before allocation?
> 
Because a few bytes can be saved this way (by not initializing pvd). The 
difference (in performance) will only be on the error path, which we 
don't care.

>> +
>> +    rc = kobject_set_name(&pvd->kset.kobj, "%s", tmr->name);
>> +    if (rc)
>> +        return ERR_PTR(rc);
>> +
>> +    pvd->kset.kobj.kset = tmr_sysfs_root;
>> +    pvd->kset.kobj.ktype = &_mr_provider_ktype;
>> +    pvd->tmr = tmr;
>> +
>> +    init_rwsem(&pvd->rwsem);
>> +
>> +    rc = kset_register(&pvd->kset);
>> +    if (rc)
>> +        return ERR_PTR(rc);
>> +
>> +    return_ptr(pvd);
>> +}
>> +
>> +DEFINE_FREE(_unregister_measurement, struct tmr_provider *,
>> +        if (!IS_ERR_OR_NULL(_T)) tsm_unregister_measurement(_T->tmr));
>> +
>> +int tsm_register_measurement(struct tsm_measurement *tmr)
>> +{
>> +    struct tmr_provider *pvd __free(_unregister_measurement);
>> +    int rc, nr;
>> +
>> +    pvd = tmr_provider_create(tmr);
>> +    if (IS_ERR(pvd))
>> +        return PTR_ERR(pvd);
>> +
>> +    nr = 0;
>> +    for (int i = 0; tmr->mrs[i].mr_name; ++i) {
>> +        // flat files are counted and skipped
>> +        if (tmr->mrs[i].mr_flags & TSM_MR_F_F) {
>> +            ++nr;
>> +            continue;
>> +        }
>> +
>> +        struct tmr_dir *mrd;
>> +        struct bin_attribute *battrs[TMR_DIR_BA__COUNT + 1] = {};
>> +        struct attribute_group agrp = {
>> +            .name = hash_algo_name[tmr->mrs[i].mr_hash],
>> +            .bin_attrs = battrs,
>> +        };
>> +
>> +        mrd = tmr_dir_create(&tmr->mrs[i], pvd);
>> +        if (IS_ERR(mrd))
>> +            return PTR_ERR(mrd);
>> +
>> +        for (int j = 0; j < TMR_DIR_BA__COUNT; ++j)
>> +            battrs[j] = &mrd->battrs[mrd->algo][j];
>> +
>> +        rc = sysfs_create_group(&mrd->kobj, &agrp);
>> +        if (rc)
>> +            return rc;
>> +    }
>> +
>> +    if (nr > 0) {
>> +        struct bin_attribute *mrfiles __free(kfree);
>> +        struct bin_attribute **battrs __free(kfree);
>> +
>> +        mrfiles = kcalloc(nr, sizeof(*mrfiles), GFP_KERNEL);
>> +        battrs = kcalloc(nr + 1, sizeof(*battrs), GFP_KERNEL);
>> +        if (!battrs || !mrfiles)
>> +            return -ENOMEM;
>> +
>> +        for (int i = 0, j = 0; tmr->mrs[i].mr_name; ++i) {
>> +            if (!(tmr->mrs[i].mr_flags & TSM_MR_F_F))
>> +                continue;
>> +
>> +            mrfiles[j].attr.name = tmr->mrs[i].mr_name;
>> +            mrfiles[j].read = tmr_digest_read;
>> +            mrfiles[j].write = tmr_digest_write;
>> +            mrfiles[j].size = tmr->mrs[i].mr_size;
>> +            mrfiles[j].private = (void *)&tmr->mrs[i];
>> +            if (tmr->mrs[i].mr_flags & TSM_MR_F_R)
>> +                mrfiles[j].attr.mode |= S_IRUGO;
>> +            if (tmr->mrs[i].mr_flags & TSM_MR_F_W)
>> +                mrfiles[j].attr.mode |= S_IWUSR | S_IWGRP;
>> +
>> +            battrs[j] = &mrfiles[j];
>> +            ++j;
>> +        }
>> +
>> +        struct attribute_group agrp = {
>> +            .bin_attrs = battrs,
>> +        };
>> +        rc = sysfs_create_group(&pvd->kset.kobj, &agrp);
>> +        if (rc)
>> +            return rc;
>> +
>> +        pvd->mrfiles = no_free_ptr(mrfiles);
>> +    }
>> +
>> +    // initial refresh of MRs
>> +    rc = tmr_call_refresh(pvd, NULL);
>> +    pvd->in_sync = !rc;
>> +
>> +    pvd = NULL; // to avoid being freed automatically
>> +    return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(tsm_register_measurement);
>> +
>> +static void tmr_put_children(struct kset *kset)
>> +{
>> +    struct kobject *p, *n;
>> +
>> +    spin_lock(&kset->list_lock);
>> +    list_for_each_entry_safe(p, n, &kset->list, entry) {
>> +        spin_unlock(&kset->list_lock);
>> +        kobject_put(p);
>> +        spin_lock(&kset->list_lock);
>> +    }
>> +    spin_unlock(&kset->list_lock);
>> +}
>> +
>> +int tsm_unregister_measurement(struct tsm_measurement *tmr)
>> +{
>> +    struct kobject *kobj;
>> +    struct tmr_provider *pvd;
>> +
>> +    kobj = kset_find_obj(tmr_sysfs_root, tmr->name);
>> +    if (!kobj)
>> +        return -ENOENT;
>> +
>> +    pvd = container_of(kobj, typeof(*pvd), kset.kobj);
>> +    if (pvd->tmr != tmr)
>> +        return -EINVAL;
>> +
>> +    tmr_put_children(&pvd->kset);
>> +    kset_unregister(&pvd->kset);
>> +    kobject_put(kobj);
>> +    return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(tsm_unregister_measurement);
>> +
>> +int tsm_mr_init(void)
>> +{
>> +    tmr_sysfs_root = kset_create_and_add("tsm", NULL, kernel_kobj);
>> +    if (!tmr_sysfs_root)
>> +        return -ENOMEM;
>> +    return 0;
>> +}
>> +
>> +void tsm_mr_exit(void)
>> +{
>> +    kset_unregister(tmr_sysfs_root);
>> +}
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_DESCRIPTION("Provide Trusted Security Module measurements via 
>> sysfs");
>> diff --git a/include/linux/tsm.h b/include/linux/tsm.h
>> index 11b0c525be30..624a7b62b85d 100644
>> --- a/include/linux/tsm.h
>> +++ b/include/linux/tsm.h
>> @@ -5,6 +5,7 @@
>>   #include <linux/sizes.h>
>>   #include <linux/types.h>
>>   #include <linux/uuid.h>
>> +#include <uapi/linux/hash_info.h>
>>   #define TSM_INBLOB_MAX 64
>>   #define TSM_OUTBLOB_MAX SZ_32K
>> @@ -109,4 +110,67 @@ struct tsm_ops {
>>   int tsm_register(const struct tsm_ops *ops, void *priv);
>>   int tsm_unregister(const struct tsm_ops *ops);
>> +
>> +/**
>> + * struct tsm_measurement_register - describes an architectural 
>> measurement register (MR)
>> + * @mr_name: name of the MR
>> + * @mr_value: buffer containing the current value of the MR
>> + * @mr_size: size of the MR - typically the digest size of @mr_hash
>> + * @mr_flags: bitwise OR of flags defined in enum 
>> tsm_measurement_register_flag
>> + * @mr_hash: optional hash identifier defined in include/uapi/linux/ 
>> hash_info.h
>> + *
>> + * A CC guest driver provides this structure to detail the 
>> measurement facility supported by the
>> + * underlying CC hardware. After registration via 
>> `tsm_register_measurement`, the CC guest driver
>> + * must retain this structure until it is unregistered using 
>> `tsm_unregister_measurement`.
>> + */
>> +struct tsm_measurement_register {
>> +    const char *mr_name;
>> +    void *mr_value;
>> +    u32 mr_size;
>> +    u32 mr_flags;
>> +    enum hash_algo mr_hash;
>> +};
>> +
>> +/**
>> + * enum tsm_measurement_register_flag - properties of an MR
>> + * @TSM_MR_F_X: this MR supports the extension semantics on write
> 
> Why not use _E? Before reading the help text, I thought _X is for execute.
> 
I was thinking of HTTP and X.509, all extensions are marked by "x".

Anyone else having a preference on _E vs. _X?

>> + * @TSM_MR_F_W: this MR is writable
>> + * @TSM_MR_F_R: this MR is readable. This should typically be set
>> + * @TSM_MR_F_L: this MR is live - writes to other MRs may change this MR
>> + * @TSM_MR_F_F: present this MR as a file (instead of a directory)
>> + * @TSM_MR_F_LIVE: shorthand for L (live) and R (readable)
>> + * @TSM_MR_F_RTMR: shorthand for LIVE and X (extensible)
>> + */
>> +enum tsm_measurement_register_flag {
>> +    TSM_MR_F_X = 1,
>> +    TSM_MR_F_W = 2,
> 
> It is not clear why you want to differentiate between write and extension.
> Please add some help text related to it.
> 
R/W is for controlling the file permission of the MR, while X is the 
semantics of the MR. I'll try to clarify.

>> +    TSM_MR_F_R = 4,
>> +    TSM_MR_F_L = 8,
>> +    TSM_MR_F_F = 16,
>> +    TSM_MR_F_LIVE = TSM_MR_F_L | TSM_MR_F_R,
>> +    TSM_MR_F_RTMR = TSM_MR_F_LIVE | TSM_MR_F_X,
>> +};
>> +
>> +#define TSM_MR_(mr, 
>> hash)                                                           \
>> +    .mr_name = #mr, .mr_size = hash##_DIGEST_SIZE, .mr_hash = 
>> HASH_ALGO_##hash, \
>> +    .mr_flags = TSM_MR_F_R
>> +
>> +/**
>> + * struct tsm_measurement - define CC specific MRs and methods for 
>> updating them
>> + * @name: name of the measurement provider
>> + * @mrs: array of MR definitions ending with mr_name set to %NULL
>> + * @refresh: invoked to update the specified MR
>> + * @extend: invoked to extend the specified MR with mr_size bytes
>> + */
>> +struct tsm_measurement {
>> +    const char *name;
>> +    const struct tsm_measurement_register *mrs;
>> +    int (*refresh)(struct tsm_measurement *tmr, const struct 
>> tsm_measurement_register *mr);
>> +    int (*extend)(struct tsm_measurement *tmr, const struct 
>> tsm_measurement_register *mr,
>> +              const u8 *data);
>> +};
>> +
>> +int tsm_register_measurement(struct tsm_measurement *tmr);
>> +int tsm_unregister_measurement(struct tsm_measurement *tmr);
>> +
>>   #endif /* __TSM_H */
>>

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