Re: [PATCH V6 5/7] KVM: selftests: add library for creating/interacting with SEV guests

Sean Christopherson
2023-03-24T18:09:06Z

On Tue, Jan 10, 2023, Peter Gonda wrote:
> Add interfaces to allow tests to create SEV guests. The additional
> requirements for SEV guests PTs and other state is encapsulated by the
> new vm_sev_create_with_one_vcpu() function. This can future be
> generalized for more vCPUs but the first set of SEV selftests in this
> series only uses a single vCPU.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: Vishal Annapurve <vannapurve@google.com>
> Cc: Ackerley Tng <ackerleytng@google.com>
> cc: Andrew Jones <andrew.jones@linux.dev>
> Originally-by: Michael Roth <michael.roth@amd.com>
> Co-developed-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Peter Gonda <pgonda@google.com>
>
> ---
> tools/arch/x86/include/asm/kvm_host.h | 1 +
> tools/testing/selftests/kvm/Makefile | 3 +-
> .../selftests/kvm/include/kvm_util_base.h | 15 +-
> .../selftests/kvm/include/x86_64/processor.h | 1 +
> .../selftests/kvm/include/x86_64/sev.h | 27 ++
> tools/testing/selftests/kvm/lib/kvm_util.c | 8 +-
> .../selftests/kvm/lib/x86_64/processor.c | 45 +++-
> tools/testing/selftests/kvm/lib/x86_64/sev.c | 254 ++++++++++++++++++
> 8 files changed, 343 insertions(+), 11 deletions(-)
> create mode 100644 tools/testing/selftests/kvm/include/x86_64/sev.h
> create mode 100644 tools/testing/selftests/kvm/lib/x86_64/sev.c
>
> diff --git a/tools/arch/x86/include/asm/kvm_host.h b/tools/arch/x86/include/asm/kvm_host.h
> index d8f48fe835fb..c95041e92fb5 100644
> --- a/tools/arch/x86/include/asm/kvm_host.h
> +++ b/tools/arch/x86/include/asm/kvm_host.h
> @@ -8,6 +8,7 @@
> struct kvm_vm_arch {
> uint64_t c_bit;
> uint64_t s_bit;
> + bool is_pt_protected;

Leftover crud from a previous version, no? I.e. can't this just use vm->protected?

> };
>
> #endif // _TOOLS_LINUX_ASM_X86_KVM_HOST_H
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 1750f91dd936..b7cfb15712d1 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -39,6 +39,7 @@ LIBKVM_x86_64 += lib/x86_64/processor.c
> LIBKVM_x86_64 += lib/x86_64/svm.c
> LIBKVM_x86_64 += lib/x86_64/ucall.c
> LIBKVM_x86_64 += lib/x86_64/vmx.c
> +LIBKVM_x86_64 += lib/x86_64/sev.c
>
> LIBKVM_aarch64 += lib/aarch64/gic.c
> LIBKVM_aarch64 += lib/aarch64/gic_v3.c
> @@ -199,7 +200,7 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
> -fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
> -I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
> -I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \
> - $(KHDR_INCLUDES)
> + $(KHDR_INCLUDES) -static -gdwarf-4

Spurious stuff from your environment, which by the way can just use EXTRA_CFLAGS,
e.g. I build selftests with

EXTRA_CFLAGS="$static -Werror -gdwarf-4"

where $static varies based on the host.

> no-pie-option := $(call try-run, echo 'int main(void) { return 0; }' | \
> $(CC) -Werror $(CFLAGS) -no-pie -x c - -o "$$TMP", -no-pie)
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index 5f3150ecfbbf..b5283bcc1d02 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -89,6 +89,13 @@ enum kvm_mem_region_type {
> NR_MEM_REGIONS,
> };
>
> +/* VM protection policy/configuration. */
> +struct protected_vm {
> + bool enabled;
> + bool has_protected_bit;
> + int8_t protected_bit;
> +};

More leftover crud.

> +
> struct kvm_vm {
> int mode;
> unsigned long type;
> @@ -711,6 +718,10 @@ static inline vm_paddr_t vm_phy_pages_alloc(struct kvm_vm *vm, size_t num,
> return _vm_phy_pages_alloc(vm, num, paddr_min, memslot, vm->protected);
> }
>
> +uint64_t vm_nr_pages_required(enum vm_guest_mode mode,
> + uint32_t nr_runnable_vcpus,
> + uint64_t extra_mem_pages);
> +

Making vm_nr_pages_required() globally visible is no longer needed (upstream
changed).

> +#endif /* SELFTEST_KVM_SEV_H */
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 0d0a7ad7632d..99983a5c5558 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -151,6 +151,7 @@ const char *vm_guest_mode_string(uint32_t i)
> [VM_MODE_P40V48_16K] = "PA-bits:40, VA-bits:48, 16K pages",
> [VM_MODE_P40V48_64K] = "PA-bits:40, VA-bits:48, 64K pages",
> [VM_MODE_PXXV48_4K] = "PA-bits:ANY, VA-bits:48, 4K pages",
> + [VM_MODE_PXXV48_4K_SEV] = "PA-bits:ANY, VA-bits:48, 4K pages",
> [VM_MODE_P47V64_4K] = "PA-bits:47, VA-bits:64, 4K pages",
> [VM_MODE_P44V64_4K] = "PA-bits:44, VA-bits:64, 4K pages",
> [VM_MODE_P36V48_4K] = "PA-bits:36, VA-bits:48, 4K pages",
> @@ -176,6 +177,7 @@ const struct vm_guest_mode_params vm_guest_mode_params[] = {
> [VM_MODE_P40V48_16K] = { 40, 48, 0x4000, 14 },
> [VM_MODE_P40V48_64K] = { 40, 48, 0x10000, 16 },
> [VM_MODE_PXXV48_4K] = { 0, 0, 0x1000, 12 },
> + [VM_MODE_PXXV48_4K_SEV] = { 0, 0, 0x1000, 12 },

Aha! An excuse to use my "mode overloading" idea[*]. Similar to concerns I had with
the UPM restricted memory stuff, adding dedicated enums for modifier is going to
be a maintenance problem. So rather than have VM_MODE_PXXV48_4K_SEV, I propose we
split @mode into a set of masks and then have a "primary mode" and a "vm type".

Note, Andrew requested using a struct, so this may need a fair bit of massaging.

[*] https://lore.kernel.org/all/YtrqVwSK42KbKckf@google.com

> +static void assert_supported_guest_mode(struct kvm_vm *vm)
> +{
> + TEST_ASSERT(vm->mode == VM_MODE_PXXV48_4K || vm->mode == VM_MODE_PXXV48_4K_SEV,
> + "Attempt to use unknown or unsupported guest mode, mode: 0x%x",
> + vm->mode);

These changes all go away if we use a modifier for the VM type.

> +}
> +
> void virt_arch_pgd_alloc(struct kvm_vm *vm)
> {
> - TEST_ASSERT(vm->mode == VM_MODE_PXXV48_4K, "Attempt to use "
> - "unknown or unsupported guest mode, mode: 0x%x", vm->mode);
> + assert_supported_guest_mode(vm);
>
> /* If needed, create page map l4 table. */
> if (!vm->pgd_created) {
> @@ -186,8 +193,7 @@ void __virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr, int level)
> uint64_t *pml4e, *pdpe, *pde;
> uint64_t *pte;
>
> - TEST_ASSERT(vm->mode == VM_MODE_PXXV48_4K,
> - "Unknown or unsupported guest mode, mode: 0x%x", vm->mode);
> + assert_supported_guest_mode(vm);
>
> TEST_ASSERT((vaddr % pg_size) == 0,
> "Virtual address not aligned,\n"
> @@ -273,11 +279,14 @@ uint64_t *__vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr,
> {
> uint64_t *pml4e, *pdpe, *pde;
>
> + TEST_ASSERT(
> + !vm->arch.is_pt_protected,
> + "Protected guests have their page tables protected so gva2gpa conversions are not possible.");

Eww, Google3 C++ "readability".

TEST_ASSERT(!vm->protected,
"Walking page tables of protected guests is impossible");

> @@ -566,6 +576,10 @@ static void vcpu_setup(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
> void kvm_arch_vm_post_create(struct kvm_vm *vm)
> {
> vm_create_irqchip(vm);
> +
> + if (vm->mode == VM_MODE_PXXV48_4K_SEV) {

Unnecesary braces.

> + sev_vm_init(vm);
> + }
> }
>
> struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id,
> @@ -1050,6 +1064,25 @@ void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits)
> }
> }
>
> +static void configure_sev_pte_masks(struct kvm_vm *vm)
> +{
> + uint32_t eax, ebx, ecx, edx, enc_bit;
> +
> + cpuid(CPUID_MEM_ENC_LEAF, &eax, &ebx, &ecx, &edx);
> + enc_bit = ebx & CPUID_EBX_CBIT_MASK;

Add X86_PROPERTY_SEV_C_BIT (or something along those lines).

> +
> + vm->arch.c_bit = 1ULL << enc_bit;
> + vm->protected = true;
> + vm->gpa_protected_mask = vm->arch.c_bit;
> +}
> +
> +void kvm_init_vm_address_properties(struct kvm_vm *vm)
> +{
> + if (vm->mode == VM_MODE_PXXV48_4K_SEV) {

Unnecessary braces as written, but having a helper is just silly.

> + configure_sev_pte_masks(vm);

if (vm->type == VM_TYPE_SEV) {
vm->protected = true;
vm->arch.c_bit = this_cpu_property(X86_PROPERTY_SEV_C_BIT);
vm->gpa_tag_mask = vm->arch.c_bit;
}

> + }
> +}

...

> +static void sev_ioctl(int cmd, void *data)
> +{
> + int ret;
> + struct sev_issue_cmd arg;
> +
> + arg.cmd = cmd;
> + arg.data = (unsigned long)data;
> + ret = ioctl(open_sev_dev_path_or_exit(), SEV_ISSUE_CMD, &arg);
> + TEST_ASSERT(ret == 0, "SEV ioctl %d failed, error: %d, fw_error: %d",
> + cmd, ret, arg.error);

This leaks the fd, and it should use kvm_ioctl(). Yean, it's not technically a
KVM ioctl(), but there's no need to reinvent the wheel.

> +}
> +
> +static void kvm_sev_ioctl(struct kvm_vm *vm, int cmd, void *data)
> +{
> + struct kvm_sev_cmd arg = {0};
> + int ret;
> +
> + arg.id = cmd;
> + arg.sev_fd = open_sev_dev_path_or_exit();
> + arg.data = (__u64)data;

Use a struct initializer:

struct kvm_sev_cmd sev_cmd = {
.id = cmd,
.sev_fd = vm->sev_fd,
.data = (unsigned long)data,
};
> +
> + ret = ioctl(vm->fd, KVM_MEMORY_ENCRYPT_OP, &arg);
> + TEST_ASSERT(
> + ret == 0,
> + "SEV KVM ioctl %d failed, rc: %i errno: %i (%s), fw_error: %d",
> + cmd, ret, errno, strerror(errno), arg.error);

Google3 horrors aside, just use vm_ioctl().

vm_ioctl(vm, KVM_MEMORY_ENCRYPT_OP, &sev_cmd);

> +}
> +
> +static void sev_register_user_region(struct kvm_vm *vm, struct userspace_mem_region *region)
> +{
> + struct kvm_enc_region range = {0};
> + int ret;
> +
> + range.addr = (__u64)region->region.userspace_addr;
> + ;
> + range.size = region->region.memory_size;
> +
> + ret = ioctl(vm->fd, KVM_MEMORY_ENCRYPT_REG_REGION, &range);
> + TEST_ASSERT(ret == 0, "failed to register user range, errno: %i\n",
> + errno);

See above.

> +}
> +
> +static void sev_launch_update_data(struct kvm_vm *vm, vm_paddr_t gpa, uint64_t size)
> +{
> + struct kvm_sev_launch_update_data ksev_update_data = {0};

These are _local_ variables, there's no need to namespace them, i.e. delete kvev_.

> +
> + pr_debug("%s: addr: 0x%lx, size: %lu\n", __func__, gpa, size);
> +
> + ksev_update_data.uaddr = (__u64)addr_gpa2hva(vm, gpa);
> + ksev_update_data.len = size;

Struct initializer.

> +
> + kvm_sev_ioctl(vm, KVM_SEV_LAUNCH_UPDATE_DATA, &ksev_update_data);
> +}
> +
> +
> +/*
> + * Iterate over set ranges within sparsebit @s. In each iteration,
> + * @range_begin and @range_end will take the beginning and end of the set
> + * range, which are of type sparsebit_idx_t.
> + *
> + * For example, if the range [3, 7] (inclusive) is set, within the
> + * iteration,@range_begin will take the value 3 and @range_end will take
> + * the value 7.
> + *
> + * Ensure that there is at least one bit set before using this macro with
> + * sparsebit_any_set(), because sparsebit_first_set() will abort if none
> + * are set.
> + */
> +#define sparsebit_for_each_set_range(s, range_begin, range_end) \
> + for (range_begin = sparsebit_first_set(s), \
> + range_end = \
> + sparsebit_next_clear(s, range_begin) - 1; \
> + range_begin && range_end; \
> + range_begin = sparsebit_next_set(s, range_end), \
> + range_end = \
> + sparsebit_next_clear(s, range_begin) - 1)

This belongs in tools/testing/selftests/kvm/include/sparsebit.h.

> +
> +/*
> + * sparsebit_next_clear() can return 0 if [x, 2**64-1] are all set, and the
> + * -1 would then cause an underflow back to 2**64 - 1. This is expected and
> + * correct.
> + *
> + * If the last range in the sparsebit is [x, y] and we try to iterate,
> + * sparsebit_next_set() will return 0, and sparsebit_next_clear() will try
> + * and find the first range, but that's correct because the condition
> + * expression would cause us to quit the loop.
> + */
> +static void encrypt_region(struct kvm_vm *vm, struct userspace_mem_region *region)
> +{
> + const struct sparsebit *protected_phy_pages =
> + region->protected_phy_pages;

Don't wrap, 3 chars in the case is fine. You didn't wrap two lines below, which
runs over by 2 chars, so spontaneous combustion is unlikely.

> + const vm_paddr_t gpa_base = region->region.guest_phys_addr;
> + const sparsebit_idx_t lowest_page_in_region = gpa_base >> vm->page_shift;
> +
> + sparsebit_idx_t i;
> + sparsebit_idx_t j;
> +
> + if (!sparsebit_any_set(protected_phy_pages))
> + return;
> +
> + sev_register_user_region(vm, region);
> +
> + sparsebit_for_each_set_range(protected_phy_pages, i, j) {
> + const uint64_t size_to_load = (j - i + 1) * vm->page_size;
> + const uint64_t offset = (i - lowest_page_in_region) * vm->page_size;
> + const uint64_t gpa = gpa_base + offset;
> +
> + sev_launch_update_data(vm, gpa, size_to_load);
> + }
> +}
> +
> +static void sev_encrypt(struct kvm_vm *vm)

Open code this in its one caller.

> +{
> + int ctr;
> + struct userspace_mem_region *region;
> +
> + hash_for_each(vm->regions.slot_hash, ctr, region, slot_node) {

> + encrypt_region(vm, region);
> + }
> +
> + vm->arch.is_pt_protected = true;

Ah, that's why is_pt_protected exists. Yeah, no. I despise that SEV doesn't
actually protect guest memory until a magic command is issued. Unless there is a
really, _really_ good reason not to treat the VM as fully protected from time zero,
let's ignore that detail in selftests.

> +}
> +
> +bool is_kvm_sev_supported(void)
> +{
> + struct sev_user_data_status sev_status;
> +
> + sev_ioctl(SEV_PLATFORM_STATUS, &sev_status);
> +
> + if (!(sev_status.api_major > SEV_FW_REQ_VER_MAJOR ||
> + (sev_status.api_major == SEV_FW_REQ_VER_MAJOR &&
> + sev_status.api_minor >= SEV_FW_REQ_VER_MINOR))) {

This needs a comment explaining what on earth the major+minor stuff is, and why
we care.

> + pr_info("SEV FW version too old. Have API %d.%d (build: %d), need %d.%d, skipping test.\n",
> + sev_status.api_major, sev_status.api_minor,
> + sev_status.build, SEV_FW_REQ_VER_MAJOR,
> + SEV_FW_REQ_VER_MINOR);

The pr_info() seems kinda pointless. If someone is running these and the firmware
is too old, I assume they're going to have to do a lot of dirty work to get the
firmware updated. And this is much easier on the eyes:

struct sev_user_data_status sev_status;

sev_ioctl(SEV_PLATFORM_STATUS, &sev_status);

return sev_status.api_major > SEV_FW_REQ_VER_MAJOR ||
(sev_status.api_major == SEV_FW_REQ_VER_MAJOR &&
sev_status.api_minor >= SEV_FW_REQ_VER_MINOR);

If the pr_info() really does add value, then do something like:

supported = sev_status.api_major > SEV_FW_REQ_VER_MAJOR ||
(sev_status.api_major == SEV_FW_REQ_VER_MAJOR &&
sev_status.api_minor >= SEV_FW_REQ_VER_MINOR);
if (!supported)
pr_info();

return supported;
> +static void sev_vm_launch(struct kvm_vm *vm, uint32_t policy)
> +{
> + struct kvm_sev_launch_start ksev_launch_start = {0};
> + struct kvm_sev_guest_status ksev_status;

See above.

> +
> + ksev_launch_start.policy = policy;
> + kvm_sev_ioctl(vm, KVM_SEV_LAUNCH_START, &ksev_launch_start);
> + kvm_sev_ioctl(vm, KVM_SEV_GUEST_STATUS, &ksev_status);
> + TEST_ASSERT(ksev_status.policy == policy, "Incorrect guest policy.");
> + TEST_ASSERT(ksev_status.state == SEV_GSTATE_LUPDATE,
> + "Unexpected guest state: %d", ksev_status.state);

Print the expected vs. actual.

> +
> + ucall_init(vm, 0);
> +
> + sev_encrypt(vm);
> +}
> +
> +static void sev_vm_launch_measure(struct kvm_vm *vm, uint8_t *measurement)
> +{
> + struct kvm_sev_launch_measure ksev_launch_measure;
> + struct kvm_sev_guest_status ksev_guest_status;
> +
> + ksev_launch_measure.len = 256;
> + ksev_launch_measure.uaddr = (__u64)measurement;
> + kvm_sev_ioctl(vm, KVM_SEV_LAUNCH_MEASURE, &ksev_launch_measure);

See above.

> +
> + kvm_sev_ioctl(vm, KVM_SEV_GUEST_STATUS, &ksev_guest_status);
> + TEST_ASSERT(ksev_guest_status.state == SEV_GSTATE_LSECRET,
> + "Unexpected guest state: %d", ksev_guest_status.state);

Expected vs. actual