On Mon, Mar 31, 2025 at 3:39 AM Stefano Garzarella <sgarz...@redhat.com> wrote:
>
> From: Stefano Garzarella <sgarz...@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.bottom...@hansenpartnership.com>
> Signed-off-by: James Bottomley <james.bottom...@hansenpartnership.com>
> Co-developed-by: Claudio Carvalho <cclau...@linux.ibm.com>
> Signed-off-by: Claudio Carvalho <cclau...@linux.ibm.com>
> Reviewed-by: Tom Lendacky <thomas.lenda...@amd.com>
> Reviewed-by: Jarkko Sakkinen <jar...@kernel.org>
> Signed-off-by: Stefano Garzarella <sgarz...@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 Glaze, PhD, CISSP, CCSP (she/her)
