Re: [PATCH v8 04/16] virt: sev-guest: Add vmpck_id to snp_guest_dev struct

From: Nikunj A. Dadhania
Date: Tue Apr 16 2024 - 01:59:31 EST

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On 4/9/2024 3:53 PM, Borislav Petkov wrote:
> On Thu, Feb 15, 2024 at 05:01:16PM +0530, Nikunj A Dadhania wrote:
>> Drop vmpck and os_area_msg_seqno pointers so that secret page layout
>> does not need to be exposed to the sev-guest driver after the rework.
>> Instead, add helper APIs to access vmpck and os_area_msg_seqno when
>> needed. Added define for maximum supported VMPCK.
>
> Do not talk about *what* the patch is doing in the commit message - that
> should be obvious from the diff itself. Rather, concentrate on the *why*
> it needs to be done.
>
> Imagine one fine day you're doing git archeology, you find the place in
> the code about which you want to find out why it was changed the way it
> is now.
>
> You do git annotate <filename> ... find the line, see the commit id and
> you do:
>
> git show <commit id>
>
> You read the commit message and there's just gibberish and nothing's
> explaining *why* that change was done. And you start scratching your
> head, trying to figure out why...
>
> I'm sure you're getting the idea.

Sure, will reword the commit message and send the patch.

>
>> Also, change function is_vmpck_empty() to snp_is_vmpck_empty() in
>> preparation for moving to sev.c.
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
>> Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
>> Tested-by: Peter Gonda <pgonda@xxxxxxxxxx>
>> ---
>> arch/x86/include/asm/sev.h | 1 +
>> drivers/virt/coco/sev-guest/sev-guest.c | 95 ++++++++++++-------------
>> 2 files changed, 48 insertions(+), 48 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
>> index 0c0b11af9f89..e4f52a606487 100644
>> --- a/arch/x86/include/asm/sev.h
>> +++ b/arch/x86/include/asm/sev.h
>> @@ -135,6 +135,7 @@ struct secrets_os_area {
>> } __packed;
>>
>> #define VMPCK_KEY_LEN 32
>> +#define VMPCK_MAX_NUM 4
>>
>> /* See the SNP spec version 0.9 for secrets page format */
>> struct snp_secrets_page_layout {
>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index 596cec03f9eb..646eb215f3c7 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -55,8 +55,7 @@ struct snp_guest_dev {
>> struct snp_derived_key_req derived_key;
>> struct snp_ext_report_req ext_report;
>> } req;
>> - u32 *os_area_msg_seqno;
>> - u8 *vmpck;
>> + unsigned int vmpck_id;
>> };
>>
>> static u32 vmpck_id;
>> @@ -66,14 +65,22 @@ MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.
>> /* Mutex to serialize the shared buffer access and command handling. */
>> static DEFINE_MUTEX(snp_cmd_mutex);
>>
>> -static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
>> +static inline u8 *snp_get_vmpck(struct snp_guest_dev *snp_dev)
>
> static functions don't need a prefix like "snp_".

Sure

>
>> {
>> - char zero_key[VMPCK_KEY_LEN] = {0};
>> + return snp_dev->layout->vmpck0 + snp_dev->vmpck_id * VMPCK_KEY_LEN;
>> +}
>>
>> - if (snp_dev->vmpck)
>> - return !memcmp(snp_dev->vmpck, zero_key, VMPCK_KEY_LEN);
>> +static inline u32 *snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
>
> Ditto.

Sure

>
>> +{
>> + return &snp_dev->layout->os_area.msg_seqno_0 + snp_dev->vmpck_id;
>> +}
>>
>> - return true;
>> +static bool snp_is_vmpck_empty(struct snp_guest_dev *snp_dev)
>> +{
>> + char zero_key[VMPCK_KEY_LEN] = {0};
>> + u8 *key = snp_get_vmpck(snp_dev);
>> +
>> + return !memcmp(key, zero_key, VMPCK_KEY_LEN);
>> }
>>
>> /*
>> @@ -95,20 +102,22 @@ static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
>> */
>> static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
>> {
>> - dev_alert(snp_dev->dev, "Disabling vmpck_id %d to prevent IV reuse.\n",
>> - vmpck_id);
>> - memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN);
>> - snp_dev->vmpck = NULL;
>> + u8 *key = snp_get_vmpck(snp_dev);
>
> Check whether is_vmpck_empty before you disable?
>
>> +
>> + dev_alert(snp_dev->dev, "Disabling vmpck_id %u to prevent IV reuse.\n",
>> + snp_dev->vmpck_id);
>> + memzero_explicit(key, VMPCK_KEY_LEN);
>> }
>>
>> static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
>> {
>> + u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
>> u64 count;
>>
>> lockdep_assert_held(&snp_cmd_mutex);
>>
>> /* Read the current message sequence counter from secrets pages */
>> - count = *snp_dev->os_area_msg_seqno;
>> + count = *os_area_msg_seqno;
>
> Why does that snp_get_os_area_msg_seqno() returns a pointer when you
> deref it here again?
>
> A function which returns a sequence number should return that number
> - not a pointer to it.
>
> Which then makes that u32 *os_area_msg_seqno redundant and you can use
> the function directly.
>
> IOW:
>
> static inline u32 snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
> {
> return snp_dev->layout->os_area.msg_seqno_0 + snp_dev->vmpck_id;

This patch removes setting of layour page in snp_dev structure.

static inline u32 snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
{
if (!platform_data)
return NULL;

return *(&platform_data->layout->os_area.msg_seqno_0 + vmpck_id);
}

> }
>

> Simple.
>
>>
>> return count + 1;
>> }
>> @@ -136,11 +145,13 @@ static u64 snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
>>
>> static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
>> {
>> + u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
>> +
>> /*
>> * The counter is also incremented by the PSP, so increment it by 2
>> * and save in secrets page.
>> */
>> - *snp_dev->os_area_msg_seqno += 2;
>> + *os_area_msg_seqno += 2;
>
> Yah, you have a getter but not a setter. You're setting it through the
> pointer.

I had a getter for getting the os_area_msg_seqno pointer, probably not a good function name.

> Do you see the imbalance in the APIs?

The msg_seqno should only be incremented by 2 (always), that was the reason to avoid a setter.

>
>> }
>>
>> static inline struct snp_guest_dev *to_snp_dev(struct file *file)
>> @@ -150,15 +161,22 @@ static inline struct snp_guest_dev *to_snp_dev(struct file *file)
>> return container_of(dev, struct snp_guest_dev, misc);
>> }
>>
>> -static struct aesgcm_ctx *snp_init_crypto(u8 *key, size_t keylen)
>> +static struct aesgcm_ctx *snp_init_crypto(struct snp_guest_dev *snp_dev)
>> {
>> struct aesgcm_ctx *ctx;
>> + u8 *key;
>> +
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> + pr_err("VM communication key VMPCK%u is null\n", vmpck_id);
>
> "Empty/invalid VMPCK%u communication key"
>
> or so.
>
> In a pre-patch, fix all your user-visible strings to say "VMPCK"
> - capitalized as it is an abbreviation.

Sure, will do.

>
>> + return NULL;
>> + }
>>
>> ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
>> if (!ctx)
>> return NULL;
>>
>> - if (aesgcm_expandkey(ctx, key, keylen, AUTHTAG_LEN)) {
>> + key = snp_get_vmpck(snp_dev);
>> + if (aesgcm_expandkey(ctx, key, VMPCK_KEY_LEN, AUTHTAG_LEN)) {
>> pr_err("Crypto context initialization failed\n");
>> kfree(ctx);
>> return NULL;
>> @@ -590,7 +608,7 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
>> mutex_lock(&snp_cmd_mutex);
>>
>> /* Check if the VMPCK is not empty */
>> - if (is_vmpck_empty(snp_dev)) {
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
>> mutex_unlock(&snp_cmd_mutex);
>> return -ENOTTY;
>> @@ -667,32 +685,14 @@ static const struct file_operations snp_guest_fops = {
>> .unlocked_ioctl = snp_guest_ioctl,
>> };
>>
>> -static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno)
>> +static bool snp_assign_vmpck(struct snp_guest_dev *dev, unsigned int vmpck_id)
>> {
>> - u8 *key = NULL;
>> + if (WARN_ON((vmpck_id + 1) > VMPCK_MAX_NUM))
>> + return false;
>
> So this will warn *and*, at the call site too. Let's tone that down.

Sure.

>
>>
>> - switch (id) {
>> - case 0:
>> - *seqno = &layout->os_area.msg_seqno_0;
>> - key = layout->vmpck0;
>> - break;
>> - case 1:
>> - *seqno = &layout->os_area.msg_seqno_1;
>> - key = layout->vmpck1;
>> - break;
>> - case 2:
>> - *seqno = &layout->os_area.msg_seqno_2;
>> - key = layout->vmpck2;
>> - break;
>> - case 3:
>> - *seqno = &layout->os_area.msg_seqno_3;
>> - key = layout->vmpck3;
>> - break;
>> - default:
>> - break;
>> - }
>
> Your commit message could explain why this is not needed, all of
> a sudden.

This was replaced by two independent APIs returning pointers to VMPCK and seqno pointer.

static inline u8 *snp_get_vmpck(unsigned int vmpck_id)
{
if (!platform_data)
return NULL;

return platform_data->layout->vmpck0 + vmpck_id * VMPCK_KEY_LEN;
}

static inline u32 *snp_get_os_area_msg_seqno(unsigned int vmpck_id)
{
if (!platform_data)
return NULL;

return &platform_data->layout->os_area.msg_seqno_0 + vmpck_id;
}

I will add more details.

>
>> + dev->vmpck_id = vmpck_id;
>>
>> - return key;
>> + return true;
>> }
>>
>> struct snp_msg_report_resp_hdr {
>> @@ -728,7 +728,7 @@ static int sev_report_new(struct tsm_report *report, void *data)
>> guard(mutex)(&snp_cmd_mutex);
>>
>> /* Check if the VMPCK is not empty */
>> - if (is_vmpck_empty(snp_dev)) {
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
>> return -ENOTTY;
>> }
>> @@ -848,21 +848,20 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>> goto e_unmap;
>>
>> ret = -EINVAL;
>> - snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
>> - if (!snp_dev->vmpck) {
>> - dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
>> + snp_dev->layout = layout;
>> + if (!snp_assign_vmpck(snp_dev, vmpck_id)) {
>> + dev_err(dev, "invalid vmpck id %u\n", vmpck_id);
>> goto e_unmap;
>> }
>>
>> /* Verify that VMPCK is not zero. */
>> - if (is_vmpck_empty(snp_dev)) {
>> - dev_err(dev, "vmpck id %d is null\n", vmpck_id);
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> + dev_err(dev, "vmpck id %u is null\n", vmpck_id);
>
> s!null!Invalid/Empty!

Okay

>
>> goto e_unmap;
>> }
>>
>> platform_set_drvdata(pdev, snp_dev);
>> snp_dev->dev = dev;
>> - snp_dev->layout = layout;
>>
>> /* Allocate the shared page used for the request and response message. */
>> snp_dev->request = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));
>> @@ -878,7 +877,7 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>> goto e_free_response;
>>
>> ret = -EIO;
>> - snp_dev->ctx = snp_init_crypto(snp_dev->vmpck, VMPCK_KEY_LEN);
>> + snp_dev->ctx = snp_init_crypto(snp_dev);
>> if (!snp_dev->ctx)
>> goto e_free_cert_data;
>>
>> @@ -903,7 +902,7 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>> if (ret)
>> goto e_free_ctx;
>>
>> - dev_info(dev, "Initialized SEV guest driver (using vmpck_id %d)\n", vmpck_id);
>> + dev_info(dev, "Initialized SEV guest driver (using vmpck_id %u)\n", vmpck_id);
>
> Yet another spelling: "vmpck_id". Unify all those in a pre-patch pls
> because it looks stupid.

Sure
>
> Thx.
>

Thanks for the review.

Regards
Nikunj

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