[PATCH v2 2/4] crypto/ccp: Support setting RAPL_DIS in SNP_INIT_EX

Tycho Andersen
2026-04-27T20:50:41Z

From the PLATYPUS [1] attack paper:

We exploit unprivileged access to the Intel Running Average Power Limit
(RAPL) interface that exposes values directly correlated with power
consumption, forming a low-resolution side channel.

The SEV firmware offers a mechanism to freeze RAPL counters across all
cores during SNP initialization via the RAPL_DIS bit in SNP_INIT_EX. The
counters remain frozen while SNP is initialized, and resume after an SNP
shutdown.

The SEV firmware also has a RAPL_DIS policy bit, allowing guests to enforce
that RAPL is disabled on a system before running. Since the kernel had no
way to set the RAPL_DIS bit during SNP init, trying to set the policy bit
would always result in a failed launch.

Allow setting the RAPL_DIS bit during SNP_INIT_EX via
struct sev_platform_init_args.

If the hardware does not support RAPL_DIS, set the rapl_disable parameter
to false so that consumers can detect when it was not actually initialized.

[1]: https://platypusattack.com/platypus.pdf

Signed-off-by: Tycho Andersen (AMD) <tycho@kernel.org>
---
drivers/crypto/ccp/sev-dev.c | 14 +++++++++++++-
include/linux/psp-sev.h | 2 ++
2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index bf54a3fadb28..6223d63e676e 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1365,8 +1365,11 @@ static int __sev_snp_init_locked(struct sev_platform_init_args *args)

sev = psp->sev_data;

- if (sev->snp_initialized)
+ if (sev->snp_initialized) {
+ if (args->rapl_disable && !sev->snp_plat_status.rapl_dis)
+ args->rapl_disable = false;
return 0;
+ }

if (!sev_version_greater_or_equal(SNP_MIN_API_MAJOR, SNP_MIN_API_MINOR)) {
dev_dbg(sev->dev, "SEV-SNP support requires firmware version >= %d:%d\n",
@@ -1376,6 +1379,12 @@ static int __sev_snp_init_locked(struct sev_platform_init_args *args)

snp_prepare();

+ if (args->rapl_disable && !(sev->snp_feat_info_0.ecx & SNP_RAPL_DISABLE_SUPPORTED)) {
+ dev_info(sev->dev,
+ "SEV: RAPL_DIS requested, but not supported\n");
+ args->rapl_disable = false;
+ }
+
/*
* Starting in SNP firmware v1.52, the SNP_INIT_EX command takes a list
* of system physical address ranges to convert into HV-fixed page
@@ -1426,6 +1435,9 @@ static int __sev_snp_init_locked(struct sev_platform_init_args *args)
data.max_snp_asid = args->max_snp_asid;
}

+ if (args->rapl_disable)
+ data.rapl_dis = 1;
+
data.init_rmp = 1;
data.list_paddr_en = 1;
data.list_paddr = __psp_pa(snp_range_list);
diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
index d5099a2baca5..55ffc098d573 100644
--- a/include/linux/psp-sev.h
+++ b/include/linux/psp-sev.h
@@ -848,11 +848,13 @@ struct sev_data_snp_shutdown_ex {
* unless psp_init_on_probe module param is set
* @max_snp_asid: When non-zero, enable ciphertext hiding and specify the
* maximum ASID that can be used for an SEV-SNP guest.
+ * @rapl_disable: Whether or not to set the RAPL_DIS bit during SNP_INIT_EX.
*/
struct sev_platform_init_args {
int error;
bool probe;
unsigned int max_snp_asid;
+ bool rapl_disable;
};

/**
--
2.53.0