Re: [PATCH v2] x86: Add a test for AMD SEV-ES #VC handling

[Tom Lendacky]

On 5/31/21 12:27 PM, Varad Gautam wrote:
> Some vmexits on a SEV-ES guest need special handling within the guest
> before exiting to the hypervisor. This must happen within the guest's
> \#VC exception handler, triggered on every non automatic exit.
> 
> Add a KUnit based test to validate Linux's VC handling. The test:
> 1. installs a kretprobe on the #VC handler (sev_es_ghcb_hv_call, to
>    access GHCB before/after the resulting VMGEXIT).
> 2. tiggers an NAE.
> 3. checks that the kretprobe was hit with the right exit_code available
>    in GHCB.
> 
> Since relying on kprobes, the test does not cover NMI contexts.

I'm not very familiar with these types of tests, so just general feedback
below.

> 
> Signed-off-by: Varad Gautam <varad.gautam@xxxxxxxx>
> ---
> v2: Add a testcase for MMIO read/write.
> 
>  arch/x86/Kconfig              |   9 ++
>  arch/x86/kernel/Makefile      |   5 ++
>  arch/x86/kernel/sev-test-vc.c | 155 ++++++++++++++++++++++++++++++++++
>  3 files changed, 169 insertions(+)
>  create mode 100644 arch/x86/kernel/sev-test-vc.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0045e1b441902..0a3c3f31813f1 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1543,6 +1543,15 @@ config AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
>  	  If set to N, then the encryption of system memory can be
>  	  activated with the mem_encrypt=on command line option.
>  
> +config AMD_MEM_ENCRYPT_TEST_VC
> +	bool "Test for AMD Secure Memory Encryption (SME) support"

I would change this to indicate that this is specifically for testing
SEV-ES support. We messed up and didn't update the AMD_MEM_ENCRYPT entry
when the SEV support was submitted.

Thanks,
Tom

> +	depends on AMD_MEM_ENCRYPT
> +	select KUNIT
> +	select FUNCTION_TRACER
> +	help
> +	  Enable KUnit-based testing for the encryption of system memory
> +	  using AMD SEV-ES. Currently only tests #VC handling.
> +
>  # Common NUMA Features
>  config NUMA
>  	bool "NUMA Memory Allocation and Scheduler Support"
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 0f66682ac02a6..360c5d33580ca 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -23,6 +23,10 @@ CFLAGS_REMOVE_head64.o = -pg
>  CFLAGS_REMOVE_sev.o = -pg
>  endif
>  
> +ifdef CONFIG_AMD_MEM_ENCRYPT_TEST_VC
> +CFLAGS_sev.o	+= -fno-ipa-sra
> +endif

Maybe add something in the commit message as to why this is needed.

> +
>  KASAN_SANITIZE_head$(BITS).o				:= n
>  KASAN_SANITIZE_dumpstack.o				:= n
>  KASAN_SANITIZE_dumpstack_$(BITS).o			:= n
> @@ -149,6 +153,7 @@ obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
>  obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
>  
>  obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
> +obj-$(CONFIG_AMD_MEM_ENCRYPT_TEST_VC)	+= sev-test-vc.o
>  ###
>  # 64 bit specific files
>  ifeq ($(CONFIG_X86_64),y)
> diff --git a/arch/x86/kernel/sev-test-vc.c b/arch/x86/kernel/sev-test-vc.c
> new file mode 100644
> index 0000000000000..2475270b844e8
> --- /dev/null
> +++ b/arch/x86/kernel/sev-test-vc.c
> @@ -0,0 +1,155 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2021 SUSE
> + *
> + * Author: Varad Gautam <varad.gautam@xxxxxxxx>
> + */
> +
> +#include <asm/cpufeature.h>
> +#include <asm/debugreg.h>
> +#include <asm/io.h>
> +#include <asm/sev-common.h>
> +#include <asm/svm.h>
> +#include <kunit/test.h>
> +#include <linux/kprobes.h>
> +
> +static struct kretprobe hv_call_krp;
> +
> +static int hv_call_krp_entry(struct kretprobe_instance *krpi,
> +				    struct pt_regs *regs)

Align with the argument above.

> +{
> +	unsigned long ghcb_vaddr = regs_get_kernel_argument(regs, 0);
> +	*((unsigned long *) krpi->data) = ghcb_vaddr;
> +
> +	return 0;
> +}
> +
> +static int hv_call_krp_ret(struct kretprobe_instance *krpi,
> +				    struct pt_regs *regs)

Align with the argument above.

> +{
> +	unsigned long ghcb_vaddr = *((unsigned long *) krpi->data);
> +	struct ghcb *ghcb = (struct ghcb *) ghcb_vaddr;
> +	struct kunit *test = current->kunit_test;
> +
> +	if (test && strstr(test->name, "sev_es_") && test->priv)
> +		cmpxchg((unsigned long *) test->priv, ghcb->save.sw_exit_code, 1);
> +
> +	return 0;
> +}
> +
> +int sev_test_vc_init(struct kunit *test)
> +{
> +	int ret;
> +
> +	if (!sev_es_active()) {
> +		pr_err("Not a SEV-ES guest. Skipping.");

Should this be a pr_info vs a pr_err?

Should you define a pr_fmt above for the pr_ messages?

> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	memset(&hv_call_krp, 0, sizeof(hv_call_krp));
> +	hv_call_krp.entry_handler = hv_call_krp_entry;
> +	hv_call_krp.handler = hv_call_krp_ret;
> +	hv_call_krp.maxactive = 100;
> +	hv_call_krp.data_size = sizeof(unsigned long);
> +	hv_call_krp.kp.symbol_name = "sev_es_ghcb_hv_call";
> +	hv_call_krp.kp.addr = 0;
> +
> +	ret = register_kretprobe(&hv_call_krp);
> +	if (ret < 0) {

Should this just be "if (ret) {"? Can a positive number be returned and if
so, what does it mean?

> +		pr_err("Could not register kretprobe. Skipping.");
> +		goto out;
> +	}
> +
> +	test->priv = kunit_kzalloc(test, sizeof(unsigned long), GFP_KERNEL);
> +	if (!test->priv) {
> +		ret = -ENOMEM;
> +		pr_err("Could not allocate. Skipping.");
> +		goto out;
> +	}
> +
> +out:
> +	return ret;
> +}
> +
> +void sev_test_vc_exit(struct kunit *test)
> +{
> +	if (test->priv)
> +		kunit_kfree(test, test->priv);
> +
> +	if (hv_call_krp.kp.addr)
> +		unregister_kretprobe(&hv_call_krp);
> +}
> +
> +#define guarded_op(kt, ec, op)				\
> +do {							\
> +	struct kunit *t = (struct kunit *) kt;		\
> +	smp_store_release((typeof(ec) *) t->priv, ec);	\
> +	op;						\
> +	KUNIT_EXPECT_EQ(t, (typeof(ec)) 1, 		\
> +		(typeof(ec)) smp_load_acquire((typeof(ec) *) t->priv));	\

I usually like seeing all the '\' characters lined up, rather than having
just the one hanging out.

Thanks,
Tom

> +} while(0)
> +
> +static void sev_es_nae_cpuid(struct kunit *test)
> +{
> +	unsigned int cpuid_fn = 0x8000001f;
> +
> +	guarded_op(test, SVM_EXIT_CPUID, native_cpuid_eax(cpuid_fn));
> +}
> +
> +static void sev_es_nae_wbinvd(struct kunit *test)
> +{
> +	guarded_op(test, SVM_EXIT_WBINVD, wbinvd());
> +}
> +
> +static void sev_es_nae_msr(struct kunit *test)
> +{
> +	guarded_op(test, SVM_EXIT_MSR, __rdmsr(MSR_IA32_TSC));
> +}
> +
> +static void sev_es_nae_dr7_rw(struct kunit *test)
> +{
> +	guarded_op(test, SVM_EXIT_WRITE_DR7,
> +		   native_set_debugreg(7, native_get_debugreg(7)));
> +}
> +
> +static void sev_es_nae_ioio(struct kunit *test)
> +{
> +	unsigned long port = 0x80;
> +	char val = 0;
> +
> +	guarded_op(test, SVM_EXIT_IOIO, val = inb(port));
> +	guarded_op(test, SVM_EXIT_IOIO, outb(val, port));
> +	guarded_op(test, SVM_EXIT_IOIO, insb(port, &val, sizeof(val)));
> +	guarded_op(test, SVM_EXIT_IOIO, outsb(port, &val, sizeof(val)));
> +}
> +
> +static void sev_es_nae_mmio(struct kunit *test)
> +{
> +	unsigned long lapic_ver_pa = 0xfee00030; /* APIC_DEFAULT_PHYS_BASE + APIC_LVR */
> +	unsigned __iomem *lapic = ioremap(lapic_ver_pa, 0x4);
> +	unsigned lapic_version = 0;
> +
> +	guarded_op(test, SVM_VMGEXIT_MMIO_READ, lapic_version = *lapic);
> +	guarded_op(test, SVM_VMGEXIT_MMIO_WRITE, *lapic = lapic_version);
> +
> +	iounmap(lapic);
> +}
> +
> +static struct kunit_case sev_test_vc_testcases[] = {
> +	KUNIT_CASE(sev_es_nae_cpuid),
> +	KUNIT_CASE(sev_es_nae_wbinvd),
> +	KUNIT_CASE(sev_es_nae_msr),
> +	KUNIT_CASE(sev_es_nae_dr7_rw),
> +	KUNIT_CASE(sev_es_nae_ioio),
> +	KUNIT_CASE(sev_es_nae_mmio),
> +	{}
> +};
> +
> +static struct kunit_suite sev_vc_test_suite = {
> +	.name = "sev_test_vc",
> +	.init = sev_test_vc_init,
> +	.exit = sev_test_vc_exit,
> +	.test_cases = sev_test_vc_testcases,
> +};
> +kunit_test_suite(sev_vc_test_suite);
>