On Thu, May 22, 2025 at 12:21:37PM +0300, Elena Reshetova wrote:
> All running enclaves and cryptographic assets (such as internal SGX
> encryption keys) are assumed to be compromised whenever an SGX-related
> microcode update occurs. To mitigate this assumed compromise the new
> supervisor SGX instruction ENCLS[EUPDATESVN] can generate fresh
> cryptographic assets.
>
> Before executing EUPDATESVN, all SGX memory must be marked as unused.
> This requirement ensures that no potentially compromised enclave
> survives the update and allows the system to safely regenerate
> cryptographic assets.
>
> Add the method to perform ENCLS[EUPDATESVN].
>
> Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
> ---
> arch/x86/kernel/cpu/sgx/encls.h | 5 +++
> arch/x86/kernel/cpu/sgx/main.c | 67 +++++++++++++++++++++++++++++++++
> 2 files changed, 72 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
> index 99004b02e2ed..d9160c89a93d 100644
> --- a/arch/x86/kernel/cpu/sgx/encls.h
> +++ b/arch/x86/kernel/cpu/sgx/encls.h
> @@ -233,4 +233,9 @@ static inline int __eaug(struct sgx_pageinfo *pginfo,
> void *addr)
> return __encls_2(EAUG, pginfo, addr);
> }
>
> +/* Attempt to update CPUSVN at runtime. */
> +static inline int __eupdatesvn(void)
> +{
> + return __encls_ret_1(EUPDATESVN, "");
> +}
> #endif /* _X86_ENCLS_H */
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index a018b01b8736..109d40c89fe8 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -16,6 +16,7 @@
> #include <linux/vmalloc.h>
> #include <asm/msr.h>
> #include <asm/sgx.h>
> +#include <asm/archrandom.h>
> #include "driver.h"
> #include "encl.h"
> #include "encls.h"
> @@ -920,6 +921,72 @@ EXPORT_SYMBOL_GPL(sgx_set_attribute);
> /* Counter to count the active SGX users */
> static atomic64_t sgx_usage_count;
>
> +/**
> + * sgx_updatesvn() - Attempt to call ENCLS[EUPDATESVN].
> + * This instruction attempts to update CPUSVN to the
> + * currently loaded microcode update SVN and generate new
> + * cryptographic assets. Must be called when EPC is empty.
> + * Most of the time, there will be no update and that's OK.
> + * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
> + * operation can be safely retried. In other failure cases,
> + * the retry should not be attempted.
> + *
> + * Return:
> + * 0: Success or not supported
> + * -EAGAIN: Can be safely retried, failure is due to lack of
> + * entropy in RNG.
> + * -EIO: Unexpected error, retries are not advisable.
> + */
> +static int sgx_update_svn(void)
> +{
> + int ret;
> +
> + /*
> + * If EUPDATESVN is not available, it is ok to
> + * silently skip it to comply with legacy behavior.
> + */
> + if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
> + return 0;
> +
> + for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
> + ret = __eupdatesvn();
> +
> + /* Stop on success or unexpected errors: */
> + if (ret != SGX_INSUFFICIENT_ENTROPY)
> + break;
> + }
> +
> + /*
> + * SVN was already up-to-date. This is the most
> + * common case.
> + */
> + if (ret == SGX_NO_UPDATE)
> + return 0;
> +
> + /*
> + * SVN update failed due to lack of entropy in DRNG.
> + * Indicate to userspace that it should retry.
> + */
> + if (ret == SGX_INSUFFICIENT_ENTROPY)
> + return -EAGAIN;
> +
> + if (!ret) {
> + /*
> + * SVN successfully updated.
> + * Let users know when the update was successful.
> + */
> + pr_info("SVN updated successfully\n");
> + return 0;
> + }
> +
> + /*
> + * EUPDATESVN was called when EPC is empty, all other error
> + * codes are unexpected.
> + */
> + ENCLS_WARN(ret, "EUPDATESVN");
> + return -EIO;
> +}
Even if unlikely() was not used I still don't agree with the order i.e.,
dealing with the success case in the middle. So I stand with my earlier
suggestion, except unlikely() (since that was a problem for David, not
going to fight over it).
BR, Jarkko
