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

[Tom Lendacky]

On 9/16/20 4:23 AM, Laszlo Ersek wrote:
> Hi Tom,

Hi Laszlo,

> 
> 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(...)
>   };
> 

Can do.

Thanks,
Tom

> 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)
>>  {
>>
>