Re: [PATCH v5 3/3] KVM: selftests: Add test for user space MSR handling

[Aaron Lewis]

On Fri, Aug 7, 2020 at 8:57 AM Alexander Graf <graf@xxxxxxxxxx> wrote:
>
> Now that we have the ability to handle MSRs from user space and also to
> select which ones we do want to prevent in-kernel KVM code from handling,
> let's add a selftest to show case and verify the API.
>
> Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>
>
> ---
>
> v2 -> v3:
>
>   - s/KVM_CAP_ADD_MSR_ALLOWLIST/KVM_CAP_X86_MSR_ALLOWLIST/g
>   - Add test to clear whitelist
>   - Adjust to reply-less API
>   - Fix asserts
>   - Actually trap on MSR_IA32_POWER_CTL writes
> ---
>  tools/testing/selftests/kvm/Makefile          |   1 +
>  .../selftests/kvm/x86_64/user_msr_test.c      | 221 ++++++++++++++++++
>  2 files changed, 222 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/user_msr_test.c
>

Please add user_msr_test to .gitignore.

> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 4a166588d99f..80d5c348354c 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -55,6 +55,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
>  TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test
>  TEST_GEN_PROGS_x86_64 += x86_64/xss_msr_test
>  TEST_GEN_PROGS_x86_64 += x86_64/debug_regs
> +TEST_GEN_PROGS_x86_64 += x86_64/user_msr_test
>  TEST_GEN_PROGS_x86_64 += clear_dirty_log_test
>  TEST_GEN_PROGS_x86_64 += demand_paging_test
>  TEST_GEN_PROGS_x86_64 += dirty_log_test
> diff --git a/tools/testing/selftests/kvm/x86_64/user_msr_test.c b/tools/testing/selftests/kvm/x86_64/user_msr_test.c
> new file mode 100644
> index 000000000000..7b149424690d
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/user_msr_test.c
> @@ -0,0 +1,221 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * tests for KVM_CAP_X86_USER_SPACE_MSR and KVM_X86_ADD_MSR_ALLOWLIST
> + *
> + * Copyright (C) 2020, Amazon Inc.
> + *
> + * This is a functional test to verify that we can deflect MSR events
> + * into user space.
> + */
> +#define _GNU_SOURCE /* for program_invocation_short_name */
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/ioctl.h>
> +
> +#include "test_util.h"
> +
> +#include "kvm_util.h"
> +#include "processor.h"
> +
> +#define VCPU_ID                  5
> +
> +u32 msr_reads, msr_writes;
> +
> +struct range_desc {
> +       struct kvm_msr_allowlist allow;
> +       void (*populate)(struct kvm_msr_allowlist *range);
> +};
> +
> +static void populate_c0000000_read(struct kvm_msr_allowlist *range)
> +{
> +       u8 *bitmap = range->bitmap;
> +       u32 idx = MSR_SYSCALL_MASK & (KVM_MSR_ALLOWLIST_MAX_LEN - 1);
> +
> +       bitmap[idx / 8] &= ~(1 << (idx % 8));
> +}
> +
> +static void populate_00000000_write(struct kvm_msr_allowlist *range)
> +{
> +       u8 *bitmap = range->bitmap;
> +       u32 idx = MSR_IA32_POWER_CTL & (KVM_MSR_ALLOWLIST_MAX_LEN - 1);
> +
> +       bitmap[idx / 8] &= ~(1 << (idx % 8));
> +}
> +
> +struct range_desc ranges[] = {
> +       {
> +               .allow = {
> +                       .flags = KVM_MSR_ALLOW_READ,
> +                       .base = 0x00000000,
> +                       .nmsrs = KVM_MSR_ALLOWLIST_MAX_LEN * BITS_PER_BYTE,
> +               },
> +       }, {
> +               .allow = {
> +                       .flags = KVM_MSR_ALLOW_WRITE,
> +                       .base = 0x00000000,
> +                       .nmsrs = KVM_MSR_ALLOWLIST_MAX_LEN * BITS_PER_BYTE,
> +               },
> +               .populate = populate_00000000_write,
> +       }, {
> +               .allow = {
> +                       .flags = KVM_MSR_ALLOW_READ | KVM_MSR_ALLOW_WRITE,
> +                       .base = 0x40000000,
> +                       .nmsrs = KVM_MSR_ALLOWLIST_MAX_LEN * BITS_PER_BYTE,
> +               },
> +       }, {
> +               .allow = {
> +                       .flags = KVM_MSR_ALLOW_READ,
> +                       .base = 0xc0000000,
> +                       .nmsrs = KVM_MSR_ALLOWLIST_MAX_LEN * BITS_PER_BYTE,
> +               },
> +               .populate = populate_c0000000_read,
> +       }, {
> +               .allow = {
> +                       .flags = KVM_MSR_ALLOW_WRITE,
> +                       .base = 0xc0000000,
> +                       .nmsrs = KVM_MSR_ALLOWLIST_MAX_LEN * BITS_PER_BYTE,
> +               },
> +       },
> +};
> +
> +static void guest_msr_calls(bool trapped)
> +{
> +       /* This goes into the in-kernel emulation */
> +       wrmsr(MSR_SYSCALL_MASK, 0);
> +
> +       if (trapped) {
> +               /* This goes into user space emulation */
> +               GUEST_ASSERT(rdmsr(MSR_SYSCALL_MASK) == MSR_SYSCALL_MASK);
> +       } else {
> +               GUEST_ASSERT(rdmsr(MSR_SYSCALL_MASK) != MSR_SYSCALL_MASK);
> +       }
> +
> +       /* If trapped == true, this goes into user space emulation */
> +       wrmsr(MSR_IA32_POWER_CTL, 0x1234);
> +
> +       /* This goes into the in-kernel emulation */
> +       rdmsr(MSR_IA32_POWER_CTL);
> +}
> +
> +static void guest_code(void)
> +{
> +       guest_msr_calls(true);
> +
> +       /*
> +        * Disable allow listing, so that the kernel
> +        * handles everything in the next round
> +        */
> +       GUEST_SYNC(0);
> +
> +       guest_msr_calls(false);
> +
> +       GUEST_DONE();
> +}
> +
> +static int handle_ucall(struct kvm_vm *vm)
> +{
> +       struct ucall uc;
> +
> +       switch (get_ucall(vm, VCPU_ID, &uc)) {
> +       case UCALL_ABORT:
> +               TEST_FAIL("Guest assertion not met");
> +               break;
> +       case UCALL_SYNC:
> +               vm_ioctl(vm, KVM_X86_CLEAR_MSR_ALLOWLIST, NULL);
> +               break;
> +       case UCALL_DONE:
> +               return 1;
> +       default:
> +               TEST_FAIL("Unknown ucall %lu", uc.cmd);
> +       }
> +
> +       return 0;
> +}
> +
> +static void handle_rdmsr(struct kvm_run *run)
> +{
> +       run->msr.data = run->msr.index;
> +       msr_reads++;
> +}
> +
> +static void handle_wrmsr(struct kvm_run *run)
> +{
> +       /* ignore */
> +       msr_writes++;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +       struct kvm_enable_cap cap = {
> +               .cap = KVM_CAP_X86_USER_SPACE_MSR,
> +               .args[0] = 1,
> +       };
> +       struct kvm_vm *vm;
> +       struct kvm_run *run;
> +       int rc;
> +       int i;
> +
> +       /* Tell stdout not to buffer its content */
> +       setbuf(stdout, NULL);
> +
> +       /* Create VM */
> +       vm = vm_create_default(VCPU_ID, 0, guest_code);
> +       vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
> +       run = vcpu_state(vm, VCPU_ID);
> +
> +       rc = kvm_check_cap(KVM_CAP_X86_USER_SPACE_MSR);
> +       TEST_ASSERT(rc, "KVM_CAP_X86_USER_SPACE_MSR is available");
> +       vm_enable_cap(vm, &cap);
> +
> +       rc = kvm_check_cap(KVM_CAP_X86_MSR_ALLOWLIST);
> +       TEST_ASSERT(rc, "KVM_CAP_X86_MSR_ALLOWLIST is available");
> +
> +       /* Set up MSR allowlist */
> +       for (i = 0; i < ARRAY_SIZE(ranges); i++) {
> +               struct kvm_msr_allowlist *a = &ranges[i].allow;
> +               u32 bitmap_size = a->nmsrs / BITS_PER_BYTE;
> +               struct kvm_msr_allowlist *range = malloc(sizeof(*a) + bitmap_size);
> +
> +               TEST_ASSERT(range, "range alloc failed (%ld bytes)\n", sizeof(*a) + bitmap_size);
> +
> +               *range = *a;
> +
> +               /* Allow everything by default */
> +               memset(range->bitmap, 0xff, bitmap_size);
> +
> +               if (ranges[i].populate)
> +                       ranges[i].populate(range);
> +
> +               vm_ioctl(vm, KVM_X86_ADD_MSR_ALLOWLIST, range);
> +       }
> +
> +       while (1) {
> +               rc = _vcpu_run(vm, VCPU_ID);
> +
> +               TEST_ASSERT(rc == 0, "vcpu_run failed: %d\n", rc);
> +
> +               switch (run->exit_reason) {
> +               case KVM_EXIT_X86_RDMSR:
> +                       handle_rdmsr(run);
> +                       break;
> +               case KVM_EXIT_X86_WRMSR:
> +                       handle_wrmsr(run);
> +                       break;
> +               case KVM_EXIT_IO:
> +                       if (handle_ucall(vm))
> +                               goto done;
> +                       break;
> +               }
> +
> +       }
> +
> +done:
> +       TEST_ASSERT(msr_reads == 1, "Handled 1 rdmsr in user space");
> +       TEST_ASSERT(msr_writes == 1, "Handled 1 wrmsr in user space");
> +
> +       kvm_vm_free(vm);
> +
> +       return 0;
> +}
> --
> 2.17.1
>
>
>
>
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