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

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 9/17/20 11:46 AM, Dr. David Alan Gilbert wrote:
> * Tom Lendacky (thomas.lendacky@xxxxxxx) wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> >
> > 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@xxxxxxx>
> > ---
> >   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;
>
> uint32_t's ?

I can change those.

> > +    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;
> > +
>
> Is that all signed off and happy from the OVMF guys?

Yes, upstream already.

> >   static SevGuestState *sev_guest;
> >   static Error *sev_mig_blocker;
> >   
> > @@ -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.
>
> It surprises me a bit it's at a fixed offset.

It's based on the end of flash having fixed offsets for the reset vector 
code. So going just before those results in a fixed offset for the first 
GUID entry. After that, more entries can be included and accessed based on 
the size value of the structure.

Thanks,
Tom

> Dave
>
> > +     */
> > +    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)
> >   {
> > --
> > 2.28.0