diff mbox series

[v5,1/4] x86/sev: add SVSM vTPM probe/send_command functions

Message ID 20250331103900.92701-2-sgarzare@redhat.com (mailing list archive)
State New
Headers show
Series Enlightened vTPM support for SVSM on SEV-SNP | expand

Commit Message

Stefano Garzarella March 31, 2025, 10:38 a.m. UTC 
From: Stefano Garzarella <sgarzare@redhat.com>

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 <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Co-developed-by: Claudio Carvalho <cclaudio@linux.ibm.com>
Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
v5:
- added stubs when !CONFIG_AMD_MEM_ENCRYPT [Dionna]
- added Jarkko's R-b
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 |  9 ++++++
 arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

Comments

Dionna Amalie Glaze April 2, 2025, 4:13 a.m. UTC | #1 
On Mon, Mar 31, 2025 at 3:39 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> From: Stefano Garzarella <sgarzare@redhat.com>
>
> 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 <James.Bottomley@HansenPartnership.com>
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Co-developed-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> v5:
> - added stubs when !CONFIG_AMD_MEM_ENCRYPT [Dionna]
> - added Jarkko's R-b
> 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 |  9 ++++++
>  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 68 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ba7999f66abe..ba7a0a327afb 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);
>
> @@ -524,6 +531,8 @@ static inline struct snp_msg_desc *snp_msg_alloc(void) { return NULL; }
>  static inline void snp_msg_free(struct snp_msg_desc *mdesc) { }
>  static inline int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
>                                          struct snp_guest_request_ioctl *rio) { return -ENODEV; }
> +static inline bool snp_svsm_vtpm_probe(void) { return false; }
> +static inline int snp_svsm_vtpm_send_command(u8 *buffer) { return -ENODEV; }
>  static inline void __init snp_secure_tsc_prepare(void) { }
>  static inline void __init snp_secure_tsc_init(void) { }
>
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index b0c1a7a57497..efb43c9d3d30 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -2625,6 +2625,65 @@ 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);
> +

How do we prevent this from causing scheduler problems when the TPM
service decides to take a really long time?
I removed the create_ek_2048 operation at boot in favor of lazily
creating it on first use.

This attest protocol uses tpm_send_command under the hood and
demonstrates the problem.
When I use this for CreatePrimary for an RSA 2048 key, the vCPU goes
out to lunch

[ 3356.509143] Sending NMI from CPU 1 to CPUs 0:
[ 2503.241673] NMI backtrace for cpu 0
[ 2503.241673] CPU: 0 PID: 462 Comm: cat Not tainted 6.6.84 #1
[ 2503.241673] Hardware name: Google Google Compute Engine/Google
Compute Engine, BIOS Google 01/01/2011
[ 2503.241673] RIP: 0010:svsm_perform_call_protocol+0x1ee/0x310
[ 2503.241673] Code: c2 48 c1 ea 20 b9 30 01 01 c0 0f 30 48 8b 3b 48
8b 43 08 48 8b 4b 10 48 8b 53 18 4c 8b 43 20 4c 8b 4b 28 c6 07
01 f3 0f 01 d9 <48> 8b 3b 45 31 d2 44 86 17 48 89 43 30 48 89 4b 38 48
89 53 40 4c
[ 2503.241673] RSP: 0018:ffffc90000f93ba8 EFLAGS: 00000012
[ 2503.241673] RAX: 0000000080000000 RBX: ffffc90000f93c98 RCX:
000000013ffe8008
[ 2503.241673] RDX: ffffffffffffffff RSI: ffff88813ffe9000 RDI:
ffff88813ffe8000
[ 2503.241673] RBP: ffffc90000f93bf8 R08: ffffffffffffffff R09:
0000000000000000
[ 2503.241673] R10: 0000000000000000 R11: 0000000080000000 R12:
0000000080000018
[ 2503.241673] R13: ffff88813ffe93f0 R14: 00000000ffffffea R15:
ffff8881bffe9000
[ 2503.241673] FS:  00007d3490351800(0000) GS:ffff88813bc00000(0000)
knlGS:0000000000000000
[ 2503.241673] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2503.241673] CR2: 00007d349032f000 CR3: 00080001012d8003 CR4:
0000000000770ef0
[ 2503.241673] PKRU: 55555554
[ 2503.241673] Call Trace:
[ 2503.241673]  <NMI>
[ 2503.241673]  ? nmi_cpu_backtrace+0xe2/0x110
[ 2503.241673]  ? nmi_cpu_backtrace_handler+0x15/0x20
[ 2503.241673]  ? nmi_handle+0x7f/0x140
[ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
[ 2503.241673]  ? default_do_nmi+0x46/0x100
[ 2503.241673]  ? exc_nmi+0x111/0x190
[ 2503.241673]  ? end_repeat_nmi+0x16/0x67
[ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
[ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
[ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
[ 2503.241673]  </NMI>
[ 2503.241673]  <TASK>
[ 2503.241673]  snp_issue_svsm_attest_req+0xa7/0xf0
[ 2503.241673]  sev_report_new+0x58e/0xb20
[ 2503.241673]  ? srso_alias_return_thunk+0x5/0xfbef5
[ 2503.241673]  tsm_report_read+0x153/0x330
[ 2503.241673]  configfs_bin_read_iter+0xbf/0x200
[ 2503.241673]  ? srso_alias_return_thunk+0x5/0xfbef5
[ 2503.241673]  vfs_read+0x25e/0x2f0
[ 2503.241673]  ksys_read+0x75/0xe0
[ 2503.241673]  do_syscall_64+0x46/0xb0
[ 2503.241673]  entry_SYSCALL_64_after_hwframe+0x78/0xe2
[ 2503.241673] RIP: 0033:0x7d348ff281cd
[ 2503.241673] Code: 31 c0 e9 d6 fe ff ff 55 48 8d 3d a6 0a 0a 00 48
89 e5 e8 c6 1c 02 00 66 0f 1f 44 00 00 80 3d 31 62 0d 00 00 74
17 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 53 c3 66 2e 0f 1f 84 00 00 00 00
00 55 48 89
[ 2503.241673] RSP: 002b:00007ffc71e50a88 EFLAGS: 00000246 ORIG_RAX:
0000000000000000
[ 2503.241673] RAX: ffffffffffffffda RBX: 00007d3490330000 RCX:
00007d348ff281cd
[ 2503.241673] RDX: 0000000000020000 RSI: 00007d3490330000 RDI:
0000000000000003
[ 2503.241673] RBP: 00007ffc71e50ab0 R08: 00007d349032f010 R09:
0000000000000000
[ 2503.241673] R10: 0000000000000022 R11: 0000000000000246 R12:
0000000000020000
[ 2503.241673] R13: 0000000000000000 R14: 0000000000000003 R15:
0000000000020000
[ 2503.241673]  </TASK>


Which doesn't seem like behavior we want, nor is it something I have
any idea how we solve with the synchronous SVSM call model.

>  static struct platform_device sev_guest_device = {
>         .name           = "sev-guest",
>         .id             = -1,
> --
> 2.49.0
>
Dionna Amalie Glaze April 2, 2025, 4:50 a.m. UTC | #2 
On Tue, Apr 1, 2025 at 9:13 PM Dionna Amalie Glaze
<dionnaglaze@google.com> wrote:
>
> On Mon, Mar 31, 2025 at 3:39 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
> >
> > From: Stefano Garzarella <sgarzare@redhat.com>
> >
> > 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 <James.Bottomley@HansenPartnership.com>
> > Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> > Co-developed-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> > Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> > Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> > ---
> > v5:
> > - added stubs when !CONFIG_AMD_MEM_ENCRYPT [Dionna]
> > - added Jarkko's R-b
> > 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 |  9 ++++++
> >  arch/x86/coco/sev/core.c   | 59 ++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 68 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> > index ba7999f66abe..ba7a0a327afb 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);
> >
> > @@ -524,6 +531,8 @@ static inline struct snp_msg_desc *snp_msg_alloc(void) { return NULL; }
> >  static inline void snp_msg_free(struct snp_msg_desc *mdesc) { }
> >  static inline int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
> >                                          struct snp_guest_request_ioctl *rio) { return -ENODEV; }
> > +static inline bool snp_svsm_vtpm_probe(void) { return false; }
> > +static inline int snp_svsm_vtpm_send_command(u8 *buffer) { return -ENODEV; }
> >  static inline void __init snp_secure_tsc_prepare(void) { }
> >  static inline void __init snp_secure_tsc_init(void) { }
> >
> > diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> > index b0c1a7a57497..efb43c9d3d30 100644
> > --- a/arch/x86/coco/sev/core.c
> > +++ b/arch/x86/coco/sev/core.c
> > @@ -2625,6 +2625,65 @@ 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);
> > +
>
> How do we prevent this from causing scheduler problems when the TPM
> service decides to take a really long time?
> I removed the create_ek_2048 operation at boot in favor of lazily
> creating it on first use.
>
> This attest protocol uses tpm_send_command under the hood and
> demonstrates the problem.
> When I use this for CreatePrimary for an RSA 2048 key, the vCPU goes
> out to lunch
>
> [ 3356.509143] Sending NMI from CPU 1 to CPUs 0:
> [ 2503.241673] NMI backtrace for cpu 0
> [ 2503.241673] CPU: 0 PID: 462 Comm: cat Not tainted 6.6.84 #1
> [ 2503.241673] Hardware name: Google Google Compute Engine/Google
> Compute Engine, BIOS Google 01/01/2011
> [ 2503.241673] RIP: 0010:svsm_perform_call_protocol+0x1ee/0x310
> [ 2503.241673] Code: c2 48 c1 ea 20 b9 30 01 01 c0 0f 30 48 8b 3b 48
> 8b 43 08 48 8b 4b 10 48 8b 53 18 4c 8b 43 20 4c 8b 4b 28 c6 07
> 01 f3 0f 01 d9 <48> 8b 3b 45 31 d2 44 86 17 48 89 43 30 48 89 4b 38 48
> 89 53 40 4c
> [ 2503.241673] RSP: 0018:ffffc90000f93ba8 EFLAGS: 00000012
> [ 2503.241673] RAX: 0000000080000000 RBX: ffffc90000f93c98 RCX:
> 000000013ffe8008
> [ 2503.241673] RDX: ffffffffffffffff RSI: ffff88813ffe9000 RDI:
> ffff88813ffe8000
> [ 2503.241673] RBP: ffffc90000f93bf8 R08: ffffffffffffffff R09:
> 0000000000000000
> [ 2503.241673] R10: 0000000000000000 R11: 0000000080000000 R12:
> 0000000080000018
> [ 2503.241673] R13: ffff88813ffe93f0 R14: 00000000ffffffea R15:
> ffff8881bffe9000
> [ 2503.241673] FS:  00007d3490351800(0000) GS:ffff88813bc00000(0000)
> knlGS:0000000000000000
> [ 2503.241673] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 2503.241673] CR2: 00007d349032f000 CR3: 00080001012d8003 CR4:
> 0000000000770ef0
> [ 2503.241673] PKRU: 55555554
> [ 2503.241673] Call Trace:
> [ 2503.241673]  <NMI>
> [ 2503.241673]  ? nmi_cpu_backtrace+0xe2/0x110
> [ 2503.241673]  ? nmi_cpu_backtrace_handler+0x15/0x20
> [ 2503.241673]  ? nmi_handle+0x7f/0x140
> [ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
> [ 2503.241673]  ? default_do_nmi+0x46/0x100
> [ 2503.241673]  ? exc_nmi+0x111/0x190
> [ 2503.241673]  ? end_repeat_nmi+0x16/0x67
> [ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
> [ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
> [ 2503.241673]  ? svsm_perform_call_protocol+0x1ee/0x310
> [ 2503.241673]  </NMI>
> [ 2503.241673]  <TASK>
> [ 2503.241673]  snp_issue_svsm_attest_req+0xa7/0xf0
> [ 2503.241673]  sev_report_new+0x58e/0xb20
> [ 2503.241673]  ? srso_alias_return_thunk+0x5/0xfbef5
> [ 2503.241673]  tsm_report_read+0x153/0x330
> [ 2503.241673]  configfs_bin_read_iter+0xbf/0x200
> [ 2503.241673]  ? srso_alias_return_thunk+0x5/0xfbef5
> [ 2503.241673]  vfs_read+0x25e/0x2f0
> [ 2503.241673]  ksys_read+0x75/0xe0
> [ 2503.241673]  do_syscall_64+0x46/0xb0
> [ 2503.241673]  entry_SYSCALL_64_after_hwframe+0x78/0xe2
> [ 2503.241673] RIP: 0033:0x7d348ff281cd
> [ 2503.241673] Code: 31 c0 e9 d6 fe ff ff 55 48 8d 3d a6 0a 0a 00 48
> 89 e5 e8 c6 1c 02 00 66 0f 1f 44 00 00 80 3d 31 62 0d 00 00 74
> 17 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 53 c3 66 2e 0f 1f 84 00 00 00 00
> 00 55 48 89
> [ 2503.241673] RSP: 002b:00007ffc71e50a88 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000000
> [ 2503.241673] RAX: ffffffffffffffda RBX: 00007d3490330000 RCX:
> 00007d348ff281cd
> [ 2503.241673] RDX: 0000000000020000 RSI: 00007d3490330000 RDI:
> 0000000000000003
> [ 2503.241673] RBP: 00007ffc71e50ab0 R08: 00007d349032f010 R09:
> 0000000000000000
> [ 2503.241673] R10: 0000000000000022 R11: 0000000000000246 R12:
> 0000000000020000
> [ 2503.241673] R13: 0000000000000000 R14: 0000000000000003 R15:
> 0000000000020000
> [ 2503.241673]  </TASK>
>

Disregard this error. I was providing the wrong command. I don't
experience any such hang now.

>
> Which doesn't seem like behavior we want, nor is it something I have
> any idea how we solve with the synchronous SVSM call model.
>
> >  static struct platform_device sev_guest_device = {
> >         .name           = "sev-guest",
> >         .id             = -1,
> > --
> > 2.49.0
> >
>
>
> --
> -Dionna Glaze, PhD, CISSP, CCSP (she/her)
diff mbox series

Patch

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ba7999f66abe..ba7a0a327afb 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);
 
@@ -524,6 +531,8 @@  static inline struct snp_msg_desc *snp_msg_alloc(void) { return NULL; }
 static inline void snp_msg_free(struct snp_msg_desc *mdesc) { }
 static inline int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req,
 					 struct snp_guest_request_ioctl *rio) { return -ENODEV; }
+static inline bool snp_svsm_vtpm_probe(void) { return false; }
+static inline int snp_svsm_vtpm_send_command(u8 *buffer) { return -ENODEV; }
 static inline void __init snp_secure_tsc_prepare(void) { }
 static inline void __init snp_secure_tsc_init(void) { }
 
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index b0c1a7a57497..efb43c9d3d30 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2625,6 +2625,65 @@  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,