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crypto: ccp - Do not initialize SNP for ioctl(SNP_CONFIG)

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Sashiko notes:

> if SEV initialization fails and KVM is actively running normal VMs, could a
> userspace process trigger this code path via /dev/sev ioctls (e.g.,
> SEV_PDH_GEN) and zero out MSR_VM_HSAVE_PA globally? Would the next VMRUN
> execution for an active VM trigger a general protection fault and crash the
> host?

Refuse to re-try initialization if SNP is not already initialized for
SNP_CONFIG.

This is technically an ABI break: before if SNP initialization failed it
could be transparently retriggered by this ioctl, and if no VMs were
running, everything worked fine. Hopefully this is enough of a corner case
that nobody will notice, but someone does, there are a few options:

* do something like symbol_get() for kvm and refuse to initialize if KVM is
  loaded
* check each cpu's HSAVE_PA for non-zero data before re-initializing
* once initialization has failed, continue to refuse to initialize until
  the ccp module is unloaded

Fixes: ceac7fb89e ("crypto: ccp - Ensure implicit SEV/SNP init and shutdown in ioctls")
Reported-by: Sashiko
Assisted-by: Gemini:gemini-3.1-pro-preview
Link: https://sashiko.dev/#/patchset/20260324161301.1353976-1-tycho%40kernel.org
CC: <stable@vger.kernel.org>
Signed-off-by: Tycho Andersen (AMD) <tycho@kernel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Tycho Andersen (AMD) 2026-05-04 10:51:47 -06:00 committed by Herbert Xu
parent f91e9dbb58
commit 08f0e65e78
1 changed files with 4 additions and 29 deletions
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33
drivers/crypto/ccp/sev-dev.c
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@ -1730,21 +1730,6 @@ static int sev_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_req
return 0;
}
static int snp_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_required)
{
int error, rc;
rc = __sev_snp_init_locked(&error, 0);
if (rc) {
argp->error = SEV_RET_INVALID_PLATFORM_STATE;
return rc;
}
*shutdown_required = true;
return 0;
}
static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
{
int state, rc;
@ -2454,8 +2439,6 @@ static int sev_ioctl_do_snp_set_config(struct sev_issue_cmd *argp, bool writable
{
struct sev_device *sev = psp_master->sev_data;
struct sev_user_data_snp_config config;
bool shutdown_required = false;
int ret, error;
if (!argp->data)
return -EINVAL;
@ -2463,21 +2446,13 @@ static int sev_ioctl_do_snp_set_config(struct sev_issue_cmd *argp, bool writable
if (!writable)
return -EPERM;
if (!sev->snp_initialized)
return -ENODEV;
if (copy_from_user(&config, (void __user *)argp->data, sizeof(config)))
return -EFAULT;
if (!sev->snp_initialized) {
ret = snp_move_to_init_state(argp, &shutdown_required);
if (ret)
return ret;
}
ret = __sev_do_cmd_locked(SEV_CMD_SNP_CONFIG, &config, &argp->error);
if (shutdown_required)
__sev_snp_shutdown_locked(&error, false);
return ret;
return __sev_do_cmd_locked(SEV_CMD_SNP_CONFIG, &config, &argp->error);
}
static int sev_ioctl_do_snp_vlek_load(struct sev_issue_cmd *argp, bool writable)