Message-ID: <20250602224459.41505-1-seanjc@google.com>
Date: Mon,  2 Jun 2025 15:44:57 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Alexander Potapenko <glider@...gle.com>, James Houghton <jthoughton@...gle.com>, 
	Peter Gonda <pgonda@...gle.com>, Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 0/2] KVM: SVM: Fix a NULL VMSA deref with MOVE_ENC_CONTEXT

Fix a NULL VMSA deref bug (which is probably the tip of the iceberg with
respect to what all can go wrong) due to a race between KVM_CREATE_VCPU and
KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM, where a non-SEV-ES vCPU can be created in
an SEV-ES VM.

Found by running syzkaller on a bare metal SEV-ES host.  C repro below.

Sean Christopherson (2):
  KVM: SVM: Reject SEV{-ES} intra host migration if vCPU creation is
    in-flight
  KVM: SVM: Initialize vmsa_pa in VMCB to INVALID_PAGE if VMSA page is
    NULL

 arch/x86/kvm/svm/sev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)


base-commit: 0ff41df1cb268fc69e703a08a57ee14ae967d0ca
-- 
2.49.0.1204.g71687c7c1d-goog

// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <sys/wait.h>

#include <linux/futex.h>
#include <linux/kvm.h>

static unsigned long long procid;

static void sleep_ms(uint64_t ms)
{
  usleep(ms * 1000);
}

static uint64_t current_time_ms(void)
{
  struct timespec ts;
  if (clock_gettime(CLOCK_MONOTONIC, &ts))
    exit(1);
  return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

static void thread_start(void* (*fn)(void*), void* arg)
{
  pthread_t th;
  pthread_attr_t attr;
  pthread_attr_init(&attr);
  pthread_attr_setstacksize(&attr, 128 << 10);
  int i = 0;
  for (; i < 100; i++) {
    if (pthread_create(&th, &attr, fn, arg) == 0) {
      pthread_attr_destroy(&attr);
      return;
    }
    if (errno == EAGAIN) {
      usleep(50);
      continue;
    }
    break;
  }
  exit(1);
}

typedef struct {
  int state;
} event_t;

static void event_init(event_t* ev)
{
  ev->state = 0;
}

static void event_reset(event_t* ev)
{
  ev->state = 0;
}

static void event_set(event_t* ev)
{
  if (ev->state)
    exit(1);
  __atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
  syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}

static void event_wait(event_t* ev)
{
  while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
    syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}

static int event_isset(event_t* ev)
{
  return __atomic_load_n(&ev->state, __ATOMIC_ACQUIRE);
}

static int event_timedwait(event_t* ev, uint64_t timeout)
{
  uint64_t start = current_time_ms();
  uint64_t now = start;
  for (;;) {
    uint64_t remain = timeout - (now - start);
    struct timespec ts;
    ts.tv_sec = remain / 1000;
    ts.tv_nsec = (remain % 1000) * 1000 * 1000;
    syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, &ts);
    if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
      return 1;
    now = current_time_ms();
    if (now - start > timeout)
      return 0;
  }
}

struct thread_t {
  int created, call;
  event_t ready, done;
};

static struct thread_t threads[16];
static void execute_call(int call);
static int running;

static void* thr(void* arg)
{
  struct thread_t* th = (struct thread_t*)arg;
  for (;;) {
    event_wait(&th->ready);
    event_reset(&th->ready);
    execute_call(th->call);
    __atomic_fetch_sub(&running, 1, __ATOMIC_RELAXED);
    event_set(&th->done);
  }
  return 0;
}

static void execute_one(void)
{
  if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {
  }
  int i, call, thread;
  for (call = 0; call < 9; call++) {
    for (thread = 0; thread < (int)(sizeof(threads) / sizeof(threads[0]));
         thread++) {
      struct thread_t* th = &threads[thread];
      if (!th->created) {
        th->created = 1;
        event_init(&th->ready);
        event_init(&th->done);
        event_set(&th->done);
        thread_start(thr, th);
      }
      if (!event_isset(&th->done))
        continue;
      event_reset(&th->done);
      th->call = call;
      __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED);
      event_set(&th->ready);
      if (call == 2 || call == 5 || call == 7)
        break;
      event_timedwait(&th->done, 50);
      break;
    }
  }
  for (i = 0; i < 100 && __atomic_load_n(&running, __ATOMIC_RELAXED); i++)
    sleep_ms(1);
}

static void loop(void)
{
  int iter = 0;
  for (; iter < 100; iter++) {
    int pid = fork();
    if (pid < 0)
      exit(1);
    if (pid == 0) {
      execute_one();
      exit(0);
    }
    int status = 0;
    uint64_t start = current_time_ms();
    for (;;) {
      sleep_ms(10);
      if (waitpid(-1, &status, WNOHANG | __WALL) == pid)
        break;
      if (current_time_ms() - start < 5000)
        continue;
      break;
    }
  }
}

uint64_t r[4] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff,
                 0xffffffffffffffff};

void execute_call(int call)
{
  switch (call) {
  case 0:
    r[1] = syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/KVM_CREATE_VM, /*type=*/0ul);
    break;
  case 3:
    r[3] = syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/KVM_CREATE_VM, /*type=*/0ul);
    break;
  case 5:
    syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/KVM_CREATE_VCPU, /*id=*/0ul);
    for (int i = 0; i < 32; i++) {
      syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/KVM_CREATE_VCPU, /*id=*/0ul);
    }
    break;
  case 6:
    *(uint64_t*)0x200000000040 = 1;
    *(uint32_t*)0x200000000048 = 8;
    *(uint32_t*)0x20000000004c = 0;
    *(uint64_t*)0x200000000050 = 0x5625e9b0;
    *(uint64_t*)0x200000000058 = 0;
    memset((void*)0x200000000060, 0, 16);
    syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/KVM_MEMORY_ENCRYPT_OP,
            /*arg=*/0x200000000040ul);
    for (int i = 0; i < 32; i++) {
      syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/KVM_MEMORY_ENCRYPT_OP,
              /*arg=*/0x200000000040ul);
    }
    break;
  case 7:
    *(uint32_t*)0x200000000080 = KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM;
    *(uint32_t*)0x200000000084 = 0;
    *(uint32_t*)0x200000000088 = r[1];
    syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/KVM_ENABLE_CAP,
            /*arg=*/0x200000000080ul);
    break;
  }
}
int main(void)
{
  syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
          /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul,
          /*fd=*/(intptr_t)-1, /*offset=*/0ul);
  syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul,
          /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/ 7ul,
          /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul,
          /*fd=*/(intptr_t)-1, /*offset=*/0ul);
  syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
          /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul,
          /*fd=*/(intptr_t)-1, /*offset=*/0ul);
  for (procid = 0; procid < 10; procid++) {
    if (fork() == 0) {
      r[0] = open("/dev/kvm", O_RDWR);
      loop();
    }
  }
  sleep(1000000);
  return 0;
}

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