Re: [PATCH v12 40/46] x86/sev: add sev=debug cmdline option to dump SNP CPUID table

Borislav Petkov
2022-03-25T09:24:57Z

On Mon, Mar 07, 2022 at 03:33:50PM -0600, Brijesh Singh wrote:
> From: Michael Roth <michael.roth@amd.com>
>
> For debugging purposes it is very useful to have a way to see the full
> contents of the SNP CPUID table provided to a guest. Add an sev=debug
> kernel command-line option to do so.
>
> Also introduce some infrastructure so that additional options can be
> specified via sev=option1[,option2] over time in a consistent manner.
>
> Suggested-by: Borislav Petkov <bp@alien8.de>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
> .../admin-guide/kernel-parameters.txt | 2 +
> Documentation/x86/x86_64/boot-options.rst | 14 +++++
> arch/x86/kernel/sev.c | 58 +++++++++++++++++++
> 3 files changed, 74 insertions(+)

I simplified the string parsing:

---
From: Michael Roth <michael.roth@amd.com>
Date: Mon, 7 Mar 2022 15:33:50 -0600
Subject: [PATCH] x86/sev: Add a sev= cmdline option

For debugging purposes it is very useful to have a way to see the full
contents of the SNP CPUID table provided to a guest. Add an sev=debug
kernel command-line option to do so.

Also introduce some infrastructure so that additional options can be
specified via sev=option1[,option2] over time in a consistent manner.

[ bp: Massage, simplify string parsing. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-41-brijesh.singh@amd.com
---
.../admin-guide/kernel-parameters.txt | 2 +
Documentation/x86/x86_64/boot-options.rst | 14 ++++++
arch/x86/kernel/sev.c | 44 +++++++++++++++++++
3 files changed, 60 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7123524a86b8..5f7fa7c141dc 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5229,6 +5229,8 @@

serialnumber [BUGS=X86-32]

+ sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst
+
shapers= [NET]
Maximal number of shapers.

diff --git a/Documentation/x86/x86_64/boot-options.rst b/Documentation/x86/x86_64/boot-options.rst
index ccb7e86bf8d9..eaecb5d89167 100644
--- a/Documentation/x86/x86_64/boot-options.rst
+++ b/Documentation/x86/x86_64/boot-options.rst
@@ -317,3 +317,17 @@ Miscellaneous
Do not use GB pages for kernel direct mappings.
gbpages
Use GB pages for kernel direct mappings.
+
+
+AMD SEV (Secure Encrypted Virtualization)
+=========================================
+Options relating to AMD SEV, specified via the following format:
+
+::
+
+ sev=option1[,option2]
+
+The available options are:
+
+ debug
+ Enable debug messages.
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index c8733725d8bf..70ecc6e2f251 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -112,6 +112,13 @@ DEFINE_STATIC_KEY_FALSE(sev_es_enable_key);

static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);

+struct sev_config {
+ __u64 debug : 1,
+ __reserved : 63;
+};
+
+static struct sev_config sev_cfg __read_mostly;
+
static __always_inline bool on_vc_stack(struct pt_regs *regs)
{
unsigned long sp = regs->sp;
@@ -2042,6 +2049,23 @@ void __init snp_abort(void)
sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
}

+static void dump_cpuid_table(void)
+{
+ const struct snp_cpuid_table *cpuid_table = snp_cpuid_get_table();
+ int i = 0;
+
+ pr_info("count=%d reserved=0x%x reserved2=0x%llx\n",
+ cpuid_table->count, cpuid_table->__reserved1, cpuid_table->__reserved2);
+
+ for (i = 0; i < SNP_CPUID_COUNT_MAX; i++) {
+ const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];
+
+ pr_info("index=%3d fn=0x%08x subfn=0x%08x: eax=0x%08x ebx=0x%08x ecx=0x%08x edx=0x%08x xcr0_in=0x%016llx xss_in=0x%016llx reserved=0x%016llx\n",
+ i, fn->eax_in, fn->ecx_in, fn->eax, fn->ebx, fn->ecx,
+ fn->edx, fn->xcr0_in, fn->xss_in, fn->__reserved);
+ }
+}
+
/*
* It is useful from an auditing/testing perspective to provide an easy way
* for the guest owner to know that the CPUID table has been initialized as
@@ -2059,6 +2083,26 @@ static int __init report_cpuid_table(void)
pr_info("Using SNP CPUID table, %d entries present.\n",
cpuid_table->count);

+ if (sev_cfg.debug)
+ dump_cpuid_table();
+
return 0;
}
arch_initcall(report_cpuid_table);
+
+static int __init init_sev_config(char *str)
+{
+ char *s;
+
+ while ((s = strsep(&str, ","))) {
+ if (!strcmp(s, "debug")) {
+ sev_cfg.debug = true;
+ continue;
+ }
+
+ pr_info("SEV command-line option '%s' was not recognized\n", s);
+ }
+
+ return 1;
+}
+__setup("sev=", init_sev_config);
--
2.35.1

--
Regards/Gruss,
Boris.

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