[v4,1/4] x86/sev: add SVSM vTPM probe/send_command functions

Commit Message

Stefano Garzarella March 24, 2025, 10:46 a.m. UTC

From: Stefano Garzarella <[e-mail]>

Add two new functions to probe and send commands to the SVSM vTPM.
They leverage the two calls defined by the AMD SVSM specification [1]
for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.

Expose these functions to be used by other modules such as a tpm
driver.

[1] "Secure VM Service Module for SEV-SNP Guests"
    Publication # 58019 Revision: 1.00

Co-developed-by: James Bottomley <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>
Co-developed-by: Claudio Carvalho <[e-mail]>
Signed-off-by: Claudio Carvalho <[e-mail]>
Reviewed-by: Tom Lendacky <[e-mail]>
Signed-off-by: Stefano Garzarella <[e-mail]>
---
v4:
- added Tom's R-b
- added functions documentation [Jarkko]
- simplified TPM_SEND_COMMAND check [Tom/Jarkko]
v3:
- removed link to the spec because those URLs are unstable [Borislav]
- squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
  in this one [Borislav]
- slimmed down snp_svsm_vtpm_probe() [Borislav]
- removed features check and any print related [Tom]
---
 arch/x86/include/asm/sev.h |  7 +++++
 arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

Comments

Dionna Amalie Glaze March 25, 2025, 4:56 p.m. UTC | #1

On Mon, Mar 24, 2025 at 3:47 AM Stefano Garzarella <[e-mail]> wrote:
>
> From: Stefano Garzarella <[e-mail]>
>
> Add two new functions to probe and send commands to the SVSM vTPM.
> They leverage the two calls defined by the AMD SVSM specification [1]
> for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.
>
> Expose these functions to be used by other modules such as a tpm
> driver.
>
> [1] "Secure VM Service Module for SEV-SNP Guests"
>     Publication # 58019 Revision: 1.00
>
> Co-developed-by: James Bottomley <[e-mail]>
> Signed-off-by: James Bottomley <[e-mail]>
> Co-developed-by: Claudio Carvalho <[e-mail]>
> Signed-off-by: Claudio Carvalho <[e-mail]>
> Reviewed-by: Tom Lendacky <[e-mail]>
> Signed-off-by: Stefano Garzarella <[e-mail]>
> ---
> v4:
> - added Tom's R-b
> - added functions documentation [Jarkko]
> - simplified TPM_SEND_COMMAND check [Tom/Jarkko]
> v3:
> - removed link to the spec because those URLs are unstable [Borislav]
> - squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
>   in this one [Borislav]
> - slimmed down snp_svsm_vtpm_probe() [Borislav]
> - removed features check and any print related [Tom]
> ---
>  arch/x86/include/asm/sev.h |  7 +++++
>  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ba7999f66abe..09471d058ce5 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -384,6 +384,10 @@ struct svsm_call {
>  #define SVSM_ATTEST_SERVICES           0
>  #define SVSM_ATTEST_SINGLE_SERVICE     1
>
> +#define SVSM_VTPM_CALL(x)              ((2ULL << 32) | (x))
> +#define SVSM_VTPM_QUERY                        0
> +#define SVSM_VTPM_CMD                  1
> +
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>
>  extern u8 snp_vmpl;
> @@ -481,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
>  int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
>                            struct snp_guest_request_ioctl *rio);
>
> +bool snp_svsm_vtpm_probe(void);
> +int snp_svsm_vtpm_send_command(u8 *buffer);
> +

These should be defined static inline with trivial definitions in the
#else case, yes?

>  void __init snp_secure_tsc_prepare(void);
>  void __init snp_secure_tsc_init(void);
>
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index 96c7bc698e6b..034aab7e76d2 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -2628,6 +2628,65 @@ static int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_dat
>         return ret;
>  }
>
> +/**
> + * snp_svsm_vtpm_probe() - Probe if SVSM provides a vTPM device
> + *
> + * This function checks that there is SVSM and that it supports at least
> + * TPM_SEND_COMMAND which is the only request we use so far.
> + *
> + * Return: true if the platform provides a vTPM SVSM device, false otherwise.
> + */
> +bool snp_svsm_vtpm_probe(void)
> +{
> +       struct svsm_call call = {};
> +
> +       /* The vTPM device is available only if a SVSM is present */
> +       if (!snp_vmpl)
> +               return false;
> +
> +       call.caa = svsm_get_caa();
> +       call.rax = SVSM_VTPM_CALL(SVSM_VTPM_QUERY);
> +
> +       if (svsm_perform_call_protocol(&call))
> +               return false;
> +
> +       /* Check platform commands contains TPM_SEND_COMMAND - platform command 8 */
> +       return call.rcx_out & BIT_ULL(8);
> +}
> +EXPORT_SYMBOL_GPL(snp_svsm_vtpm_probe);
> +
> +/**
> + * snp_svsm_vtpm_send_command() - execute a vTPM operation on SVSM
> + * @buffer: A buffer used to both send the command and receive the response.
> + *
> + * This function executes a SVSM_VTPM_CMD call as defined by
> + * "Secure VM Service Module for SEV-SNP Guests" Publication # 58019 Revision: 1.00
> + *
> + * All command request/response buffers have a common structure as specified by
> + * the following table:
> + *     Byte      Size       In/Out    Description
> + *     Offset    (Bytes)
> + *     0x000     4          In        Platform command
> + *                          Out       Platform command response size
> + *
> + * Each command can build upon this common request/response structure to create
> + * a structure specific to the command.
> + * See include/linux/tpm_svsm.h for more details.
> + *
> + * Return: 0 on success, -errno on failure
> + */
> +int snp_svsm_vtpm_send_command(u8 *buffer)
> +{
> +       struct svsm_call call = {};
> +
> +       call.caa = svsm_get_caa();
> +       call.rax = SVSM_VTPM_CALL(SVSM_VTPM_CMD);
> +       call.rcx = __pa(buffer);
> +
> +       return svsm_perform_call_protocol(&call);
> +}
> +EXPORT_SYMBOL_GPL(snp_svsm_vtpm_send_command);
> +
>  static struct platform_device sev_guest_device = {
>         .name           = "sev-guest",
>         .id             = -1,
> --
> 2.49.0
>

Stefano Garzarella March 25, 2025, 5:20 p.m. UTC | #2

On Tue, Mar 25, 2025 at 09:56:53AM -0700, Dionna Amalie Glaze wrote:
>On Mon, Mar 24, 2025 at 3:47 AM Stefano Garzarella <[e-mail]> wrote:
>>
>> From: Stefano Garzarella <[e-mail]>
>>
>> Add two new functions to probe and send commands to the SVSM vTPM.
>> They leverage the two calls defined by the AMD SVSM specification [1]
>> for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.
>>
>> Expose these functions to be used by other modules such as a tpm
>> driver.
>>
>> [1] "Secure VM Service Module for SEV-SNP Guests"
>>     Publication # 58019 Revision: 1.00
>>
>> Co-developed-by: James Bottomley <[e-mail]>
>> Signed-off-by: James Bottomley <[e-mail]>
>> Co-developed-by: Claudio Carvalho <[e-mail]>
>> Signed-off-by: Claudio Carvalho <[e-mail]>
>> Reviewed-by: Tom Lendacky <[e-mail]>
>> Signed-off-by: Stefano Garzarella <[e-mail]>
>> ---
>> v4:
>> - added Tom's R-b
>> - added functions documentation [Jarkko]
>> - simplified TPM_SEND_COMMAND check [Tom/Jarkko]
>> v3:
>> - removed link to the spec because those URLs are unstable [Borislav]
>> - squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
>>   in this one [Borislav]
>> - slimmed down snp_svsm_vtpm_probe() [Borislav]
>> - removed features check and any print related [Tom]
>> ---
>>  arch/x86/include/asm/sev.h |  7 +++++
>>  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 66 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
>> index ba7999f66abe..09471d058ce5 100644
>> --- a/arch/x86/include/asm/sev.h
>> +++ b/arch/x86/include/asm/sev.h
>> @@ -384,6 +384,10 @@ struct svsm_call {
>>  #define SVSM_ATTEST_SERVICES           0
>>  #define SVSM_ATTEST_SINGLE_SERVICE     1
>>
>> +#define SVSM_VTPM_CALL(x)              ((2ULL << 32) | (x))
>> +#define SVSM_VTPM_QUERY                        0
>> +#define SVSM_VTPM_CMD                  1
>> +
>>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>>
>>  extern u8 snp_vmpl;
>> @@ -481,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
>>  int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
>>                            struct snp_guest_request_ioctl *rio);
>>
>> +bool snp_svsm_vtpm_probe(void);
>> +int snp_svsm_vtpm_send_command(u8 *buffer);
>> +
>
>These should be defined static inline with trivial definitions in the
>#else case, yes?

For now the only user of those is the tpm_svsm driver which is build 
only if CONFIG_AMD_MEM_ENCRYPT is defined, so there should be no 
problem, but you are right, better to follow the other functions and 
define the stubs

I'll fix in v5, good catch!

Thanks,
Stefano

Jarkko Sakkinen March 26, 2025, 5:12 p.m. UTC | #3

On Mon, Mar 24, 2025 at 11:46:46AM +0100, Stefano Garzarella wrote:
> From: Stefano Garzarella <[e-mail]>
> 
> Add two new functions to probe and send commands to the SVSM vTPM.
> They leverage the two calls defined by the AMD SVSM specification [1]
> for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.
> 
> Expose these functions to be used by other modules such as a tpm
> driver.
> 
> [1] "Secure VM Service Module for SEV-SNP Guests"
>     Publication # 58019 Revision: 1.00
> 
> Co-developed-by: James Bottomley <[e-mail]>
> Signed-off-by: James Bottomley <[e-mail]>
> Co-developed-by: Claudio Carvalho <[e-mail]>
> Signed-off-by: Claudio Carvalho <[e-mail]>
> Reviewed-by: Tom Lendacky <[e-mail]>
> Signed-off-by: Stefano Garzarella <[e-mail]>
> ---
> v4:
> - added Tom's R-b
> - added functions documentation [Jarkko]
> - simplified TPM_SEND_COMMAND check [Tom/Jarkko]
> v3:
> - removed link to the spec because those URLs are unstable [Borislav]
> - squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
>   in this one [Borislav]
> - slimmed down snp_svsm_vtpm_probe() [Borislav]
> - removed features check and any print related [Tom]
> ---
>  arch/x86/include/asm/sev.h |  7 +++++
>  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ba7999f66abe..09471d058ce5 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -384,6 +384,10 @@ struct svsm_call {
>  #define SVSM_ATTEST_SERVICES		0
>  #define SVSM_ATTEST_SINGLE_SERVICE	1
>  
> +#define SVSM_VTPM_CALL(x)		((2ULL << 32) | (x))
> +#define SVSM_VTPM_QUERY			0
> +#define SVSM_VTPM_CMD			1
> +
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  
>  extern u8 snp_vmpl;
> @@ -481,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
>  int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
>  			   struct snp_guest_request_ioctl *rio);
>  
> +bool snp_svsm_vtpm_probe(void);
> +int snp_svsm_vtpm_send_command(u8 *buffer);
> +
>  void __init snp_secure_tsc_prepare(void);
>  void __init snp_secure_tsc_init(void);
>  
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index 96c7bc698e6b..034aab7e76d2 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -2628,6 +2628,65 @@ static int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_dat
>  	return ret;
>  }
>  
> +/**
> + * snp_svsm_vtpm_probe() - Probe if SVSM provides a vTPM device
> + *
> + * This function checks that there is SVSM and that it supports at least
> + * TPM_SEND_COMMAND which is the only request we use so far.
> + *
> + * Return: true if the platform provides a vTPM SVSM device, false otherwise.
> + */
> +bool snp_svsm_vtpm_probe(void)
> +{
> +	struct svsm_call call = {};
> +
> +	/* The vTPM device is available only if a SVSM is present */
> +	if (!snp_vmpl)
> +		return false;
> +
> +	call.caa = svsm_get_caa();
> +	call.rax = SVSM_VTPM_CALL(SVSM_VTPM_QUERY);
> +
> +	if (svsm_perform_call_protocol(&call))
> +		return false;
> +
> +	/* Check platform commands contains TPM_SEND_COMMAND - platform command 8 */
> +	return call.rcx_out & BIT_ULL(8);
> +}
> +EXPORT_SYMBOL_GPL(snp_svsm_vtpm_probe);
> +
> +/**
> + * snp_svsm_vtpm_send_command() - execute a vTPM operation on SVSM
> + * @buffer: A buffer used to both send the command and receive the response.
> + *
> + * This function executes a SVSM_VTPM_CMD call as defined by
> + * "Secure VM Service Module for SEV-SNP Guests" Publication # 58019 Revision: 1.00
> + *
> + * All command request/response buffers have a common structure as specified by
> + * the following table:
> + *     Byte      Size       In/Out    Description
> + *     Offset    (Bytes)
> + *     0x000     4          In        Platform command
> + *                          Out       Platform command response size
> + *
> + * Each command can build upon this common request/response structure to create
> + * a structure specific to the command.
> + * See include/linux/tpm_svsm.h for more details.
> + *
> + * Return: 0 on success, -errno on failure
> + */
> +int snp_svsm_vtpm_send_command(u8 *buffer)
> +{
> +	struct svsm_call call = {};
> +
> +	call.caa = svsm_get_caa();
> +	call.rax = SVSM_VTPM_CALL(SVSM_VTPM_CMD);
> +	call.rcx = __pa(buffer);
> +
> +	return svsm_perform_call_protocol(&call);
> +}
> +EXPORT_SYMBOL_GPL(snp_svsm_vtpm_send_command);
> +
>  static struct platform_device sev_guest_device = {
>  	.name		= "sev-guest",
>  	.id		= -1,
> -- 
> 2.49.0
> 
> 

This looks good enough as far as I'm concerned:

Reviewed-by: Jarkko Sakkinen <[e-mail]>

BR, Jarkko

Jarkko Sakkinen March 26, 2025, 5:14 p.m. UTC | #4

On Tue, Mar 25, 2025 at 06:20:48PM +0100, Stefano Garzarella wrote:
> On Tue, Mar 25, 2025 at 09:56:53AM -0700, Dionna Amalie Glaze wrote:
> > On Mon, Mar 24, 2025 at 3:47 AM Stefano Garzarella <[e-mail]> wrote:
> > > 
> > > From: Stefano Garzarella <[e-mail]>
> > > 
> > > Add two new functions to probe and send commands to the SVSM vTPM.
> > > They leverage the two calls defined by the AMD SVSM specification [1]
> > > for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.
> > > 
> > > Expose these functions to be used by other modules such as a tpm
> > > driver.
> > > 
> > > [1] "Secure VM Service Module for SEV-SNP Guests"
> > >     Publication # 58019 Revision: 1.00
> > > 
> > > Co-developed-by: James Bottomley <[e-mail]>
> > > Signed-off-by: James Bottomley <[e-mail]>
> > > Co-developed-by: Claudio Carvalho <[e-mail]>
> > > Signed-off-by: Claudio Carvalho <[e-mail]>
> > > Reviewed-by: Tom Lendacky <[e-mail]>
> > > Signed-off-by: Stefano Garzarella <[e-mail]>
> > > ---
> > > v4:
> > > - added Tom's R-b
> > > - added functions documentation [Jarkko]
> > > - simplified TPM_SEND_COMMAND check [Tom/Jarkko]
> > > v3:
> > > - removed link to the spec because those URLs are unstable [Borislav]
> > > - squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
> > >   in this one [Borislav]
> > > - slimmed down snp_svsm_vtpm_probe() [Borislav]
> > > - removed features check and any print related [Tom]
> > > ---
> > >  arch/x86/include/asm/sev.h |  7 +++++
> > >  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 66 insertions(+)
> > > 
> > > diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> > > index ba7999f66abe..09471d058ce5 100644
> > > --- a/arch/x86/include/asm/sev.h
> > > +++ b/arch/x86/include/asm/sev.h
> > > @@ -384,6 +384,10 @@ struct svsm_call {
> > >  #define SVSM_ATTEST_SERVICES           0
> > >  #define SVSM_ATTEST_SINGLE_SERVICE     1
> > > 
> > > +#define SVSM_VTPM_CALL(x)              ((2ULL << 32) | (x))
> > > +#define SVSM_VTPM_QUERY                        0
> > > +#define SVSM_VTPM_CMD                  1
> > > +
> > >  #ifdef CONFIG_AMD_MEM_ENCRYPT
> > > 
> > >  extern u8 snp_vmpl;
> > > @@ -481,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
> > >  int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
> > >                            struct snp_guest_request_ioctl *rio);
> > > 
> > > +bool snp_svsm_vtpm_probe(void);
> > > +int snp_svsm_vtpm_send_command(u8 *buffer);
> > > +
> > 
> > These should be defined static inline with trivial definitions in the
> > #else case, yes?
> 
> For now the only user of those is the tpm_svsm driver which is build only if
> CONFIG_AMD_MEM_ENCRYPT is defined, so there should be no problem, but you
> are right, better to follow the other functions and define the stubs
> 
> I'll fix in v5, good catch!

Only denoting here that you can keep my reviewed-by in the v5 for
this despite the minor change.

> 
> Thanks,
> Stefano
> 

BR, Jarkko

Stefano Garzarella March 27, 2025, 9:59 a.m. UTC | #5

On Wed, Mar 26, 2025 at 07:14:22PM +0200, Jarkko Sakkinen wrote:
>On Tue, Mar 25, 2025 at 06:20:48PM +0100, Stefano Garzarella wrote:
>> On Tue, Mar 25, 2025 at 09:56:53AM -0700, Dionna Amalie Glaze wrote:
>> > On Mon, Mar 24, 2025 at 3:47 AM Stefano Garzarella <[e-mail]> wrote:
>> > >
>> > > From: Stefano Garzarella <[e-mail]>
>> > >
>> > > Add two new functions to probe and send commands to the SVSM vTPM.
>> > > They leverage the two calls defined by the AMD SVSM specification [1]
>> > > for the vTPM protocol: SVSM_VTPM_QUERY and SVSM_VTPM_CMD.
>> > >
>> > > Expose these functions to be used by other modules such as a tpm
>> > > driver.
>> > >
>> > > [1] "Secure VM Service Module for SEV-SNP Guests"
>> > >     Publication # 58019 Revision: 1.00
>> > >
>> > > Co-developed-by: James Bottomley <[e-mail]>
>> > > Signed-off-by: James Bottomley <[e-mail]>
>> > > Co-developed-by: Claudio Carvalho <[e-mail]>
>> > > Signed-off-by: Claudio Carvalho <[e-mail]>
>> > > Reviewed-by: Tom Lendacky <[e-mail]>
>> > > Signed-off-by: Stefano Garzarella <[e-mail]>
>> > > ---
>> > > v4:
>> > > - added Tom's R-b
>> > > - added functions documentation [Jarkko]
>> > > - simplified TPM_SEND_COMMAND check [Tom/Jarkko]
>> > > v3:
>> > > - removed link to the spec because those URLs are unstable [Borislav]
>> > > - squashed "x86/sev: add SVSM call macros for the vTPM protocol" patch
>> > >   in this one [Borislav]
>> > > - slimmed down snp_svsm_vtpm_probe() [Borislav]
>> > > - removed features check and any print related [Tom]
>> > > ---
>> > >  arch/x86/include/asm/sev.h |  7 +++++
>> > >  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
>> > >  2 files changed, 66 insertions(+)
>> > >
>> > > diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
>> > > index ba7999f66abe..09471d058ce5 100644
>> > > --- a/arch/x86/include/asm/sev.h
>> > > +++ b/arch/x86/include/asm/sev.h
>> > > @@ -384,6 +384,10 @@ struct svsm_call {
>> > >  #define SVSM_ATTEST_SERVICES           0
>> > >  #define SVSM_ATTEST_SINGLE_SERVICE     1
>> > >
>> > > +#define SVSM_VTPM_CALL(x)              ((2ULL << 32) | (x))
>> > > +#define SVSM_VTPM_QUERY                        0
>> > > +#define SVSM_VTPM_CMD                  1
>> > > +
>> > >  #ifdef CONFIG_AMD_MEM_ENCRYPT
>> > >
>> > >  extern u8 snp_vmpl;
>> > > @@ -481,6 +485,9 @@ void snp_msg_free(struct snp_msg_desc *mdesc);
>> > >  int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
>> > >                            struct snp_guest_request_ioctl *rio);
>> > >
>> > > +bool snp_svsm_vtpm_probe(void);
>> > > +int snp_svsm_vtpm_send_command(u8 *buffer);
>> > > +
>> >
>> > These should be defined static inline with trivial definitions in the
>> > #else case, yes?
>>
>> For now the only user of those is the tpm_svsm driver which is build only if
>> CONFIG_AMD_MEM_ENCRYPT is defined, so there should be no problem, but you
>> are right, better to follow the other functions and define the stubs
>>
>> I'll fix in v5, good catch!
>
>Only denoting here that you can keep my reviewed-by in the v5 for
>this despite the minor change.

Thanks for pointing that out!
Stefano

Patch

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ba7999f66abe..09471d058ce5 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -384,6 +384,10 @@  struct svsm_call {
 #define SVSM_ATTEST_SERVICES		0
 #define SVSM_ATTEST_SINGLE_SERVICE	1
 
+#define SVSM_VTPM_CALL(x)		((2ULL << 32) | (x))
+#define SVSM_VTPM_QUERY			0
+#define SVSM_VTPM_CMD			1
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 
 extern u8 snp_vmpl;
@@ -481,6 +485,9 @@  void snp_msg_free(struct snp_msg_desc *mdesc);
 int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
 			   struct snp_guest_request_ioctl *rio);
 
+bool snp_svsm_vtpm_probe(void);
+int snp_svsm_vtpm_send_command(u8 *buffer);
+
 void __init snp_secure_tsc_prepare(void);
 void __init snp_secure_tsc_init(void);
 
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 96c7bc698e6b..034aab7e76d2 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2628,6 +2628,65 @@  static int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_dat
 	return ret;
 }
 
+/**
+ * snp_svsm_vtpm_probe() - Probe if SVSM provides a vTPM device
+ *
+ * This function checks that there is SVSM and that it supports at least
+ * TPM_SEND_COMMAND which is the only request we use so far.
+ *
+ * Return: true if the platform provides a vTPM SVSM device, false otherwise.
+ */
+bool snp_svsm_vtpm_probe(void)
+{
+	struct svsm_call call = {};
+
+	/* The vTPM device is available only if a SVSM is present */
+	if (!snp_vmpl)
+		return false;
+
+	call.caa = svsm_get_caa();
+	call.rax = SVSM_VTPM_CALL(SVSM_VTPM_QUERY);
+
+	if (svsm_perform_call_protocol(&call))
+		return false;
+
+	/* Check platform commands contains TPM_SEND_COMMAND - platform command 8 */
+	return call.rcx_out & BIT_ULL(8);
+}
+EXPORT_SYMBOL_GPL(snp_svsm_vtpm_probe);
+
+/**
+ * snp_svsm_vtpm_send_command() - execute a vTPM operation on SVSM
+ * @buffer: A buffer used to both send the command and receive the response.
+ *
+ * This function executes a SVSM_VTPM_CMD call as defined by
+ * "Secure VM Service Module for SEV-SNP Guests" Publication # 58019 Revision: 1.00
+ *
+ * All command request/response buffers have a common structure as specified by
+ * the following table:
+ *     Byte      Size       In/Out    Description
+ *     Offset    (Bytes)
+ *     0x000     4          In        Platform command
+ *                          Out       Platform command response size
+ *
+ * Each command can build upon this common request/response structure to create
+ * a structure specific to the command.
+ * See include/linux/tpm_svsm.h for more details.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int snp_svsm_vtpm_send_command(u8 *buffer)
+{
+	struct svsm_call call = {};
+
+	call.caa = svsm_get_caa();
+	call.rax = SVSM_VTPM_CALL(SVSM_VTPM_CMD);
+	call.rcx = __pa(buffer);
+
+	return svsm_perform_call_protocol(&call);
+}
+EXPORT_SYMBOL_GPL(snp_svsm_vtpm_send_command);
+
 static struct platform_device sev_guest_device = {
 	.name		= "sev-guest",
 	.id		= -1,