Re: [PATCH v2 08/10] i386/sev: Implement ConfidentialGuestSupport functions for SEV

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Apr 03, 2024 at 12:11:39PM +0100, Roy Hopkins wrote:
> The ConfidentialGuestSupport object defines a number of virtual
> functions that are called during processing of IGVM directives to query
> or configure initial guest state. In order to support processing of IGVM
> files, these functions need to be implemented by relevant isolation
> hardware support code such as SEV.
> 
> This commit implements the required functions for SEV-ES and adds
> support for processing IGVM files for configuring the guest.
> 
> Signed-off-by: Roy Hopkins <roy.hopkins@suse.com>
> ---
>  target/i386/sev.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 137 insertions(+)
> 
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 31dfdc3fe5..46313e7024 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -37,6 +37,7 @@
>  #include "qapi/qapi-commands-misc-target.h"
>  #include "exec/confidential-guest-support.h"
>  #include "hw/i386/pc.h"
> +#include "hw/i386/e820_memory_layout.h"
>  #include "exec/address-spaces.h"
>  
>  #define TYPE_SEV_GUEST "sev-guest"
> @@ -170,6 +171,9 @@ static const char *const sev_fw_errlist[] = {
>  
>  #define SEV_FW_MAX_ERROR      ARRAY_SIZE(sev_fw_errlist)
>  
> +static int sev_launch_update_data(SevGuestState *sev_guest, uint8_t *addr,
> +                                  uint64_t len);
> +
>  static int
>  sev_ioctl(int fd, int cmd, void *data, int *error)
>  {
> @@ -304,6 +308,14 @@ sev_guest_finalize(Object *obj)
>  {
>  }
>  
> +static int cgs_check_support(ConfidentialGuestPlatformType platform,
> +                             uint16_t platform_version, uint8_t highest_vtl,
> +                             uint64_t shared_gpa_boundary)
> +{
> +    return (((platform == CGS_PLATFORM_SEV_ES) && sev_es_enabled()) ||
> +            ((platform == CGS_PLATFORM_SEV) && sev_enabled())) ? 1 : 0;
> +}
> +
>  static void sev_apply_cpu_context(CPUState *cpu)
>  {
>      SevGuestState *sev_guest = SEV_GUEST(MACHINE(qdev_get_machine())->cgs);
> @@ -384,6 +396,54 @@ static void sev_apply_cpu_context(CPUState *cpu)
>      }
>  }
>  
> +static int check_vmsa_supported(const struct sev_es_save_area *vmsa)
> +{
> +    struct sev_es_save_area vmsa_check;
> +    size_t i;
> +    /*
> +     * Clear all supported fields so we can then check the entire structure
> +     * is zero.
> +     */
> +    memcpy(&vmsa_check, vmsa, sizeof(struct sev_es_save_area));
> +    memset(&vmsa_check.es, 0, sizeof(vmsa_check.es));
> +    memset(&vmsa_check.cs, 0, sizeof(vmsa_check.cs));
> +    memset(&vmsa_check.ss, 0, sizeof(vmsa_check.ss));
> +    memset(&vmsa_check.ds, 0, sizeof(vmsa_check.ds));
> +    memset(&vmsa_check.fs, 0, sizeof(vmsa_check.fs));
> +    memset(&vmsa_check.gs, 0, sizeof(vmsa_check.gs));
> +    vmsa_check.efer = 0;
> +    vmsa_check.cr0 = 0;
> +    vmsa_check.cr3 = 0;
> +    vmsa_check.cr4 = 0;
> +    vmsa_check.xcr0 = 0;
> +    vmsa_check.dr6 = 0;
> +    vmsa_check.dr7 = 0;
> +    vmsa_check.rax = 0;
> +    vmsa_check.rcx = 0;
> +    vmsa_check.rdx = 0;
> +    vmsa_check.rbx = 0;
> +    vmsa_check.rsp = 0;
> +    vmsa_check.rbp = 0;
> +    vmsa_check.rsi = 0;
> +    vmsa_check.rdi = 0;
> +    vmsa_check.r8 = 0;
> +    vmsa_check.r9 = 0;
> +    vmsa_check.r10 = 0;
> +    vmsa_check.r11 = 0;
> +    vmsa_check.r12 = 0;
> +    vmsa_check.r13 = 0;
> +    vmsa_check.r14 = 0;
> +    vmsa_check.r15 = 0;
> +    vmsa_check.rip = 0;
> +
> +    for (i = 0; i < sizeof(vmsa_check); ++i) {
> +        if (((uint8_t *)&vmsa_check)[i]) {
> +            return 0;
> +        }
> +    }
> +    return 1;

Can this just be:

   return !buffer_is_zero(vmsa_check, sizeof(vmsa_check))


> +}
> +
>  static int sev_set_cpu_context(uint16_t cpu_index, const void *ctx,
>                                 uint32_t ctx_len, hwaddr gpa)
>  {
> @@ -446,6 +506,77 @@ static int sev_set_cpu_context(uint16_t cpu_index, const void *ctx,
>      return 0;
>  }
>  
> +static int cgs_set_guest_state(hwaddr gpa, uint8_t *ptr, uint64_t len,
> +                               ConfidentialGuestPageType memory_type,
> +                               uint16_t cpu_index, Error **errp)
> +{
> +    SevGuestState *sev = SEV_GUEST(MACHINE(qdev_get_machine())->cgs);
> +    int ret = 1;

This results in a return '1' in some errors, but several of the callers
are checking '< 0' for the error condition. This variable is redundant
anyway, i'd suggest just putting 'return -1' calls after error_setg

> +
> +    if (!sev_enabled()) {
> +        error_setg(errp, "%s: attempt to configure guest memory, but SEV "
> +                     "is not enabled",
> +                     __func__);
> +    } else if (memory_type == CGS_PAGE_TYPE_VMSA) {
> +        if (!sev_es_enabled()) {
> +            error_setg(errp,
> +                       "%s: attempt to configure initial VMSA, but SEV-ES "
> +                       "is not supported",
> +                       __func__);
> +        } else {
> +            if (!check_vmsa_supported((const struct sev_es_save_area *)ptr)) {
> +                error_setg(errp,
> +                           "%s: The VMSA contains fields that are not "
> +                           "synchronized with KVM. Continuing would result in "
> +                           "either unpredictable guest behavior, or a "
> +                           "mismatched launch measurement.",
> +                           __func__);
> +            } else {
> +                ret = sev_set_cpu_context(cpu_index, ptr, len, gpa);

This needs to set 'errp' if 'ret' is non-zero, or assert
that it is always zer0.

> +            }
> +        }
> +    } else if ((memory_type == CGS_PAGE_TYPE_ZERO) ||
> +               (memory_type == CGS_PAGE_TYPE_NORMAL)) {
> +        ret = sev_launch_update_data(sev, ptr, len);

Likewise needs to set 'errp' or assert.

> +    } else if (memory_type != CGS_PAGE_TYPE_UNMEASURED) {
> +        error_setg(
> +            errp,
> +            "%s: attempted to configure guest memory to use memory_type %d, "
> +            "but this type is not supported",
> +            __func__, (int)memory_type);
> +    }
> +    return ret;
> +}

With regards,
Daniel
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