Re: [PATCH v3 3/5] sev/i386: Allow AP booting under SEV-ES

[Laszlo Ersek]

Hi Tom,

sorry for the random feedback -- I haven't followed (and don't really
intend to follow) the QEMU side of the feature. Just one style idea:

On 09/15/20 23:29, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> When SEV-ES is enabled, it is not possible modify the guests register
> state after it has been initially created, encrypted and measured.
> 
> Normally, an INIT-SIPI-SIPI request is used to boot the AP. However, the
> hypervisor cannot emulate this because it cannot update the AP register
> state. For the very first boot by an AP, the reset vector CS segment
> value and the EIP value must be programmed before the register has been
> encrypted and measured.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  accel/kvm/kvm-all.c    | 64 ++++++++++++++++++++++++++++++++++++++++++
>  accel/stubs/kvm-stub.c |  5 ++++
>  hw/i386/pc_sysfw.c     | 10 ++++++-
>  include/sysemu/kvm.h   | 16 +++++++++++
>  include/sysemu/sev.h   |  3 ++
>  target/i386/kvm.c      |  2 ++
>  target/i386/sev.c      | 51 +++++++++++++++++++++++++++++++++
>  7 files changed, 150 insertions(+), 1 deletion(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 63ef6af9a1..20725b0368 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -39,6 +39,7 @@
>  #include "qemu/main-loop.h"
>  #include "trace.h"
>  #include "hw/irq.h"
> +#include "sysemu/kvm.h"
>  #include "sysemu/sev.h"
>  #include "qapi/visitor.h"
>  #include "qapi/qapi-types-common.h"
> @@ -120,6 +121,12 @@ struct KVMState
>      /* memory encryption */
>      void *memcrypt_handle;
>      int (*memcrypt_encrypt_data)(void *handle, uint8_t *ptr, uint64_t len);
> +    int (*memcrypt_save_reset_vector)(void *handle, void *flash_ptr,
> +                                      uint64_t flash_size, uint32_t *addr);
> +
> +    unsigned int reset_cs;
> +    unsigned int reset_ip;
> +    bool reset_valid;
>  
>      /* For "info mtree -f" to tell if an MR is registered in KVM */
>      int nr_as;
> @@ -239,6 +246,62 @@ int kvm_memcrypt_encrypt_data(uint8_t *ptr, uint64_t len)
>      return 1;
>  }
>  
> +void kvm_memcrypt_set_reset_vector(CPUState *cpu)
> +{
> +    X86CPU *x86;
> +    CPUX86State *env;
> +
> +    /* Only update if we have valid reset information */
> +    if (!kvm_state->reset_valid) {
> +        return;
> +    }
> +
> +    /* Do not update the BSP reset state */
> +    if (cpu->cpu_index == 0) {
> +        return;
> +    }
> +
> +    x86 = X86_CPU(cpu);
> +    env = &x86->env;
> +
> +    cpu_x86_load_seg_cache(env, R_CS, 0xf000, kvm_state->reset_cs, 0xffff,
> +                           DESC_P_MASK | DESC_S_MASK | DESC_CS_MASK |
> +                           DESC_R_MASK | DESC_A_MASK);
> +
> +    env->eip = kvm_state->reset_ip;
> +}
> +
> +int kvm_memcrypt_save_reset_vector(void *flash_ptr, uint64_t flash_size)
> +{
> +    CPUState *cpu;
> +    uint32_t addr;
> +    int ret;
> +
> +    if (kvm_memcrypt_enabled() &&
> +        kvm_state->memcrypt_save_reset_vector) {
> +
> +        addr = 0;
> +        ret = 
> kvm_state->memcrypt_save_reset_vector(kvm_state->memcrypt_handle,
> +                                                    flash_ptr, flash_size,
> +                                                    &addr);
> +        if (ret) {
> +            return ret;
> +        }
> +
> +        if (addr) {
> +            kvm_state->reset_cs = addr & 0xffff0000;
> +            kvm_state->reset_ip = addr & 0x0000ffff;
> +            kvm_state->reset_valid = true;
> +
> +            CPU_FOREACH(cpu) {
> +                kvm_memcrypt_set_reset_vector(cpu);
> +            }
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  /* Called with KVMMemoryListener.slots_lock held */
>  static KVMSlot *kvm_get_free_slot(KVMMemoryListener *kml)
>  {
> @@ -2193,6 +2256,7 @@ static int kvm_init(MachineState *ms)
>          }
>  
>          kvm_state->memcrypt_encrypt_data = sev_encrypt_data;
> +        kvm_state->memcrypt_save_reset_vector = sev_es_save_reset_vector;
>      }
>  
>      ret = kvm_arch_init(ms, s);
> diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c
> index 82f118d2df..3aece9b513 100644
> --- a/accel/stubs/kvm-stub.c
> +++ b/accel/stubs/kvm-stub.c
> @@ -114,6 +114,11 @@ int kvm_memcrypt_encrypt_data(uint8_t *ptr, uint64_t len)
>    return 1;
>  }
>  
> +int kvm_memcrypt_save_reset_vector(void *flash_ptr, uint64_t flash_size)
> +{
> +    return -ENOSYS;
> +}
> +
>  #ifndef CONFIG_USER_ONLY
>  int kvm_irqchip_add_msi_route(KVMState *s, int vector, PCIDevice *dev)
>  {
> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
> index b6c0822fe3..321ff94261 100644
> --- a/hw/i386/pc_sysfw.c
> +++ b/hw/i386/pc_sysfw.c
> @@ -156,7 +156,8 @@ static void pc_system_flash_map(PCMachineState *pcms,
>      PFlashCFI01 *system_flash;
>      MemoryRegion *flash_mem;
>      void *flash_ptr;
> -    int ret, flash_size;
> +    uint64_t flash_size;
> +    int ret;
>  
>      assert(PC_MACHINE_GET_CLASS(pcms)->pci_enabled);
>  
> @@ -204,6 +205,13 @@ static void pc_system_flash_map(PCMachineState *pcms,
>              if (kvm_memcrypt_enabled()) {
>                  flash_ptr = memory_region_get_ram_ptr(flash_mem);
>                  flash_size = memory_region_size(flash_mem);
> +
> +                ret = kvm_memcrypt_save_reset_vector(flash_ptr, flash_size);
> +                if (ret) {
> +                    error_report("failed to locate and/or save reset 
> vector");
> +                    exit(1);
> +                }
> +
>                  ret = kvm_memcrypt_encrypt_data(flash_ptr, flash_size);
>                  if (ret) {
>                      error_report("failed to encrypt pflash rom");
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index b4174d941c..f74cfa85ab 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -247,6 +247,22 @@ bool kvm_memcrypt_enabled(void);
>   */
>  int kvm_memcrypt_encrypt_data(uint8_t *ptr, uint64_t len);
>  
> +/**
> + * kvm_memcrypt_set_reset_vector - sets the CS/IP value for the AP if SEV-ES
> + *                                 is active.
> + */
> +void kvm_memcrypt_set_reset_vector(CPUState *cpu);
> +
> +/**
> + * kvm_memcrypt_save_reset_vector - locates and saves the reset vector to be
> + *                                  used as the initial CS/IP value for APs
> + *                                  if SEV-ES is active.
> + *
> + * Return: 1 SEV-ES is active and failed to locate a valid reset vector
> + *         0 SEV-ES is not active or successfully located and saved the
> + *           reset vector address
> + */
> +int kvm_memcrypt_save_reset_vector(void *flash_prt, uint64_t flash_size);
>  
>  #ifdef NEED_CPU_H
>  #include "cpu.h"
> diff --git a/include/sysemu/sev.h b/include/sysemu/sev.h
> index 98c1ec8d38..5198e5a621 100644
> --- a/include/sysemu/sev.h
> +++ b/include/sysemu/sev.h
> @@ -18,4 +18,7 @@
>  
>  void *sev_guest_init(const char *id);
>  int sev_encrypt_data(void *handle, uint8_t *ptr, uint64_t len);
> +int sev_es_save_reset_vector(void *handle, void *flash_ptr,
> +                             uint64_t flash_size, uint32_t *addr);
> +
>  #endif
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 6f18d940a5..10eaba8943 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -1912,6 +1912,8 @@ void kvm_arch_reset_vcpu(X86CPU *cpu)
>      }
>      /* enabled by default */
>      env->poll_control_msr = 1;
> +
> +    kvm_memcrypt_set_reset_vector(CPU(cpu));
>  }
>  
>  void kvm_arch_do_init_vcpu(X86CPU *cpu)
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 5055b1fe00..6ddefc65fa 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -70,6 +70,19 @@ struct SevGuestState {
>  #define DEFAULT_GUEST_POLICY    0x1 /* disable debug */
>  #define DEFAULT_SEV_DEVICE      "/dev/sev"
>  
> +/* SEV Information Block GUID = 00f771de-1a7e-4fcb-890e-68c77e2fb44e */
> +#define SEV_INFO_BLOCK_GUID \
> +    "\xde\x71\xf7\x00\x7e\x1a\xcb\x4f\x89\x0e\x68\xc7\x7e\x2f\xb4\x4e"
> +
> +typedef struct __attribute__((__packed__)) SevInfoBlock {
> +    /* SEV-ES Reset Vector Address */
> +    uint32_t reset_addr;
> +
> +    /* SEV Information Block size and GUID */
> +    uint16_t size;
> +    char guid[16];
> +} SevInfoBlock;
> +
>  static SevGuestState *sev_guest;
>  static Error *sev_mig_blocker;
>  

Can we replace "char guid[16]" with "QemuUUID guid"?

Also, can we replace the SEV_INFO_BLOCK_GUID macro with a static const
structure, initialized with UUID_LE()?

Something like

  static const QemuUUID sev_info_block_guid_le = {
      .data = UUID_LE(...)
  };

Thanks
Laszlo

> @@ -833,6 +846,44 @@ sev_encrypt_data(void *handle, uint8_t *ptr, uint64_t 
> len)
>      return 0;
>  }
>  
> +int
> +sev_es_save_reset_vector(void *handle, void *flash_ptr, uint64_t flash_size,
> +                         uint32_t *addr)
> +{
> +    SevInfoBlock *info;
> +
> +    assert(handle);
> +
> +    /*
> +     * Initialize the address to zero. An address of zero with a successful
> +     * return code indicates that SEV-ES is not active.
> +     */
> +    *addr = 0;
> +    if (!sev_es_enabled()) {
> +        return 0;
> +    }
> +
> +    /*
> +     * Extract the AP reset vector for SEV-ES guests by locating the SEV 
> GUID.
> +     * The SEV GUID is located 32 bytes from the end of the flash. Use this
> +     * address to base the SEV information block.
> +     */
> +    info = flash_ptr + flash_size - 0x20 - sizeof(*info);
> +    if (memcmp(info->guid, SEV_INFO_BLOCK_GUID, 16)) {
> +        error_report("SEV information block not found in pflash rom");
> +        return 1;
> +    }
> +
> +    if (!info->reset_addr) {
> +        error_report("SEV-ES reset address is zero");
> +        return 1;
> +    }
> +
> +    *addr = info->reset_addr;
> +
> +    return 0;
> +}
> +
>  static void
>  sev_register_types(void)
>  {
>