Re: [RFC 07/16] KVM: selftests: add SEV boot tests

[Michael Roth <michael.roth@amd.com>]

On Fri, Oct 15, 2021 at 07:55:53PM -0700, Krish Sadhukhan wrote:
> 
> On 10/6/21 1:37 PM, Michael Roth wrote:
> > A common aspect of booting SEV guests is checking related CPUID/MSR
> > bits and accessing shared/private memory. Add a basic test to cover
> > this.
> > 
> > This test will be expanded to cover basic boot of SEV-ES and SEV-SNP in
> > subsequent patches.
> > 
> > Signed-off-by: Michael Roth <michael.roth@amd.com>
> > ---
> >   tools/testing/selftests/kvm/.gitignore        |   1 +
> >   tools/testing/selftests/kvm/Makefile          |   1 +
> >   .../selftests/kvm/x86_64/sev_all_boot_test.c  | 252 ++++++++++++++++++
> >   3 files changed, 254 insertions(+)
> >   create mode 100644 tools/testing/selftests/kvm/x86_64/sev_all_boot_test.c
> > 
> > diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
> > index 0709af0144c8..824f100bec2a 100644
> > --- a/tools/testing/selftests/kvm/.gitignore
> > +++ b/tools/testing/selftests/kvm/.gitignore
> > @@ -38,6 +38,7 @@
> >   /x86_64/xen_vmcall_test
> >   /x86_64/xss_msr_test
> >   /x86_64/vmx_pmu_msrs_test
> > +/x86_64/sev_all_boot_test
> >   /access_tracking_perf_test
> >   /demand_paging_test
> >   /dirty_log_test
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index c7a5e1c69e0c..aa8901bdbd22 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -72,6 +72,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/tsc_msrs_test
> >   TEST_GEN_PROGS_x86_64 += x86_64/vmx_pmu_msrs_test
> >   TEST_GEN_PROGS_x86_64 += x86_64/xen_shinfo_test
> >   TEST_GEN_PROGS_x86_64 += x86_64/xen_vmcall_test
> > +TEST_GEN_PROGS_x86_64 += x86_64/sev_all_boot_test
> >   TEST_GEN_PROGS_x86_64 += access_tracking_perf_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/sev_all_boot_test.c b/tools/testing/selftests/kvm/x86_64/sev_all_boot_test.c
> > new file mode 100644
> > index 000000000000..8df7143ac17d
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/x86_64/sev_all_boot_test.c
> > @@ -0,0 +1,252 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Basic SEV boot tests.
> > + *
> > + * Copyright (C) 2021 Advanced Micro Devices
> > + */
> > +#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"
> > +#include "svm_util.h"
> > +#include "linux/psp-sev.h"
> > +#include "sev.h"
> > +
> > +#define VCPU_ID			2
> > +#define PAGE_SIZE		4096
> > +#define PAGE_STRIDE		32
> > +
> > +#define SHARED_PAGES		8192
> > +#define SHARED_VADDR_MIN	0x1000000
> > +
> > +#define PRIVATE_PAGES		2048
> > +#define PRIVATE_VADDR_MIN	(SHARED_VADDR_MIN + SHARED_PAGES * PAGE_SIZE)
> > +
> > +#define TOTAL_PAGES		(512 + SHARED_PAGES + PRIVATE_PAGES)
> > +
> > +static void fill_buf(uint8_t *buf, size_t pages, size_t stride, uint8_t val)
> > +{
> > +	int i, j;
> > +
> > +	for (i = 0; i < pages; i++)
> > +		for (j = 0; j < PAGE_SIZE; j += stride)
> > +			buf[i * PAGE_SIZE + j] = val;
> > +}
> > +
> > +static bool check_buf(uint8_t *buf, size_t pages, size_t stride, uint8_t val)
> > +{
> > +	int i, j;
> > +
> > +	for (i = 0; i < pages; i++)
> > +		for (j = 0; j < PAGE_SIZE; j += stride)
> > +			if (buf[i * PAGE_SIZE + j] != val)
> > +				return false;
> > +
> > +	return true;
> > +}
> > +
> > +static void guest_test_start(struct sev_sync_data *sync)
> > +{
> > +	/* Initial guest check-in. */
> > +	sev_guest_sync(sync, 1, 0);
> > +}
> > +
> > +static void check_test_start(struct kvm_vm *vm, struct sev_sync_data *sync)
> > +{
> > +	struct kvm_run *run;
> > +
> > +	run = vcpu_state(vm, VCPU_ID);
> > +	vcpu_run(vm, VCPU_ID);
> > +
> > +	/* Initial guest check-in. */
> > +	sev_check_guest_sync(run, sync, 1);
> > +}
> > +
> > +static void
> > +guest_test_common(struct sev_sync_data *sync, uint8_t *shared_buf, uint8_t *private_buf)
> > +{
> > +	bool success;
> > +
> > +	/* Initial check-in for common. */
> > +	sev_guest_sync(sync, 100, 0);
> > +
> > +	/* Ensure initial shared pages are intact. */
> > +	success = check_buf(shared_buf, SHARED_PAGES, PAGE_STRIDE, 0x41);
> > +	SEV_GUEST_ASSERT(sync, 103, success);
> > +
> > +	/* Ensure initial private pages are intact/encrypted. */
> > +	success = check_buf(private_buf, PRIVATE_PAGES, PAGE_STRIDE, 0x42);
> > +	SEV_GUEST_ASSERT(sync, 104, success);
> > +
> > +	/* Ensure host userspace can't read newly-written encrypted data. */
> > +	fill_buf(private_buf, PRIVATE_PAGES, PAGE_STRIDE, 0x43);
> > +
> > +	sev_guest_sync(sync, 200, 0);
> > +
> > +	/* Ensure guest can read newly-written shared data from host. */
> > +	success = check_buf(shared_buf, SHARED_PAGES, PAGE_STRIDE, 0x44);
> > +	SEV_GUEST_ASSERT(sync, 201, success);
> > +
> > +	/* Ensure host can read newly-written shared data from guest. */
> > +	fill_buf(shared_buf, SHARED_PAGES, PAGE_STRIDE, 0x45);
> > +
> > +	sev_guest_sync(sync, 300, 0);
> > +}
> > +
> > +static void
> > +check_test_common(struct kvm_vm *vm, struct sev_sync_data *sync,
> > +		  uint8_t *shared_buf, uint8_t *private_buf)
> > +{
> > +	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
> > +	bool success;
> > +
> > +	/* Initial guest check-in. */
> > +	vcpu_run(vm, VCPU_ID);
> > +	sev_check_guest_sync(run, sync, 100);
> > +
> > +	/* Ensure initial private pages are intact/encrypted. */
> > +	success = check_buf(private_buf, PRIVATE_PAGES, PAGE_STRIDE, 0x42);
> > +	TEST_ASSERT(!success, "Initial guest memory not encrypted!");
> > +
> > +	vcpu_run(vm, VCPU_ID);
> > +	sev_check_guest_sync(run, sync, 200);
> > +
> > +	/* Ensure host userspace can't read newly-written encrypted data. */
> > +	success = check_buf(private_buf, PRIVATE_PAGES, PAGE_STRIDE, 0x43);
> > +	TEST_ASSERT(!success, "Modified guest memory not encrypted!");
> > +
> > +	/* Ensure guest can read newly-written shared data from host. */
> > +	fill_buf(shared_buf, SHARED_PAGES, PAGE_STRIDE, 0x44);
> > +
> > +	vcpu_run(vm, VCPU_ID);
> > +	sev_check_guest_sync(run, sync, 300);
> > +
> > +	/* Ensure host can read newly-written shared data from guest. */
> > +	success = check_buf(shared_buf, SHARED_PAGES, PAGE_STRIDE, 0x45);
> > +	TEST_ASSERT(success, "Host can't read shared guest memory!");
> > +}
> > +
> > +static void
> > +guest_test_done(struct sev_sync_data *sync)
> > +{
> > +	sev_guest_done(sync, 10000, 0);
> > +}
> > +
> > +static void
> > +check_test_done(struct kvm_vm *vm, struct sev_sync_data *sync)
> > +{
> > +	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
> > +
> > +	vcpu_run(vm, VCPU_ID);
> > +	sev_check_guest_done(run, sync, 10000);
> > +}
> > +
> > +static void __attribute__((__flatten__))
> > +guest_sev_code(struct sev_sync_data *sync, uint8_t *shared_buf, uint8_t *private_buf)
> > +{
> > +	uint32_t eax, ebx, ecx, edx;
> > +	uint64_t sev_status;
> > +
> > +	guest_test_start(sync);
> > +
> > +	/* Check SEV CPUID bit. */
> > +	eax = 0x8000001f;
> > +	ecx = 0;
> > +	cpuid(&eax, &ebx, &ecx, &edx);
> > +	SEV_GUEST_ASSERT(sync, 2, eax & (1 << 1));
> > +
> > +	/* Check SEV MSR bit. */
> > +	sev_status = rdmsr(MSR_AMD64_SEV);
> > +	SEV_GUEST_ASSERT(sync, 3, (sev_status & 0x1) == 1);
> > +
> Is there any need to do the cpuid and MSR tests every time the guest code is
> executed ?

It seems like a good sanity check that KVM is setting the expected bits
(via KVM_GET_SUPPORTED_CPUID) for SEV guests. This is also a fairly
common example of the sort of things a guest would do during boot to
detect/initialize SEV-related functionality.

It becomes a little more useful for the SEV-ES/SEV-SNP tests, where cpuid
instructions cause a #VC exception, which in turn leads to a VMGExit and
exercises the host KVM's handling of host-guest communiction via GHCB
MSR/GHCB page.

> > +	guest_test_common(sync, shared_buf, private_buf);
> > +
> > +	guest_test_done(sync);
> > +}
> > +
> > +static void
> > +setup_test_common(struct sev_vm *sev, void *guest_code, vm_vaddr_t *sync_vaddr,
> > +		  vm_vaddr_t *shared_vaddr, vm_vaddr_t *private_vaddr)
> > +{
> > +	struct kvm_vm *vm = sev_get_vm(sev);
> > +	uint8_t *shared_buf, *private_buf;
> > +
> > +	/* Set up VCPU and initial guest kernel. */
> > +	vm_vcpu_add_default(vm, VCPU_ID, guest_code);
> > +	kvm_vm_elf_load(vm, program_invocation_name);
> > +
> > +	/* Set up shared sync buffer. */
> > +	*sync_vaddr = vm_vaddr_alloc_shared(vm, PAGE_SIZE, 0);
> > +
> > +	/* Set up buffer for reserved shared memory. */
> > +	*shared_vaddr = vm_vaddr_alloc_shared(vm, SHARED_PAGES * PAGE_SIZE,
> > +					      SHARED_VADDR_MIN);
> > +	shared_buf = addr_gva2hva(vm, *shared_vaddr);
> > +	fill_buf(shared_buf, SHARED_PAGES, PAGE_STRIDE, 0x41);
> > +
> > +	/* Set up buffer for reserved private memory. */
> > +	*private_vaddr = vm_vaddr_alloc(vm, PRIVATE_PAGES * PAGE_SIZE,
> > +					PRIVATE_VADDR_MIN);
> > +	private_buf = addr_gva2hva(vm, *private_vaddr);
> > +	fill_buf(private_buf, PRIVATE_PAGES, PAGE_STRIDE, 0x42);
> > +}
> > +
> > +static void test_sev(void *guest_code, uint64_t policy)
> > +{
> > +	vm_vaddr_t sync_vaddr, shared_vaddr, private_vaddr;
> > +	uint8_t *shared_buf, *private_buf;
> > +	struct sev_sync_data *sync;
> > +	uint8_t measurement[512];
> > +	struct sev_vm *sev;
> > +	struct kvm_vm *vm;
> > +	int i;
> > +
> > +	sev = sev_vm_create(policy, TOTAL_PAGES);
> > +	if (!sev)
> > +		return;
> > +	vm = sev_get_vm(sev);
> > +
> > +	setup_test_common(sev, guest_code, &sync_vaddr, &shared_vaddr, &private_vaddr);
> > +
> > +	/* Set up guest params. */
> > +	vcpu_args_set(vm, VCPU_ID, 4, sync_vaddr, shared_vaddr, private_vaddr);
> > +
> > +	sync = addr_gva2hva(vm, sync_vaddr);
> > +	shared_buf = addr_gva2hva(vm, shared_vaddr);
> > +	private_buf = addr_gva2hva(vm, private_vaddr);
> > +
> > +	/* Allocations/setup done. Encrypt initial guest payload. */
> > +	sev_vm_launch(sev);
> > +
> > +	/* Dump the initial measurement. A test to actually verify it would be nice. */
> > +	sev_vm_measure(sev, measurement);
> > +	pr_info("guest measurement: ");
> > +	for (i = 0; i < 32; ++i)
> > +		pr_info("%02x", measurement[i]);
> > +	pr_info("\n");
> > +
> > +	sev_vm_launch_finish(sev);
> Since the above section of this function is actually setup code and is not
> running the test yet, it is best placed in a setup function. My suggestion
> is that you place the above section into a function called
> setup_test_common() and within that function you further separate out the
> SEV-related setup into a function called setup_test_sev() or something
> similar. Then call the top-level setup function from within main().

That makes sense. I'll try to rework this according to your suggestions.

> > +
> > +	/* Guest is ready to run. Do the tests. */
> > +	check_test_start(vm, sync);
> > +	check_test_common(vm, sync, shared_buf, private_buf);
> > +	check_test_done(vm, sync);
> 
> These function names can be better. These functions are not just checking
> the result, they are actually running the guest code. So, may be, calling
> them 'test_start, test_common and test_done are better. I would just

Will do.

> collapse them and place their code in test_sev() only if you separate the
> out the setup code as I suggested above.

Hmm, I did it that way because in the guest_{sev,sev_es,sev_snp}_code
routines there are some type-specific checks that happen before
guest_test_done(), so it made sense to have that in a separate routine,
and seemed more readable to then also have check_test_done() separate to
pair with it. But I'll see if I can rework that a bit.

> 
> > +
> > +	sev_vm_free(sev);
> > +}
> > +
> > +int main(int argc, char *argv[])
> > +{
> > +	/* SEV tests */
> > +	test_sev(guest_sev_code, SEV_POLICY_NO_DBG);
> > +	test_sev(guest_sev_code, 0);
> > +
> > +	return 0;
> > +}