x86/sev: Check SME/SEV support in CPUID first

commit 009767dbf42ac0dbe3cf48c1ee224f6b778aa85a upstream.

The first two bits of the CPUID leaf 0x8000001F EAX indicate whether SEV
or SME is supported, respectively. It's better to check whether SEV or
SME is actually supported before accessing the MSR_AMD64_SEV to check
whether SEV or SME is enabled.

This is both a bare-metal issue and a guest/VM issue. Since the first
generation Hygon Dhyana CPU doesn't support the MSR_AMD64_SEV, reading that
MSR results in a #GP - either directly from hardware in the bare-metal
case or via the hypervisor (because the RDMSR is actually intercepted)
in the guest/VM case, resulting in a failed boot. And since this is very
early in the boot phase, rdmsrl_safe()/native_read_msr_safe() can't be
used.

So check the CPUID bits first, before accessing the MSR.

 [ tlendacky: Expand and improve commit message. ]
 [ bp: Massage commit message. ]

Fixes: eab696d8e8b9 ("x86/sev: Do not require Hypervisor CPUID bit for SEV guests")
Signed-off-by: Pu Wen <puwen@hygon.cn>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@vger.kernel.org> # v5.10+
Link: https://lkml.kernel.org/r/20210602070207.2480-1-puwen@hygon.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index a19374d2610132ee94d78ee5f675d7004236aaa0..65f599e9075bc358dfbba84bfb96dddd045d01a5 100644 (file)
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -504,10 +504,6 @@ void __init sme_enable(struct boot_params *bp)
 #define AMD_SME_BIT    BIT(0)
 #define AMD_SEV_BIT    BIT(1)
 
-       /* Check the SEV MSR whether SEV or SME is enabled */
-       sev_status   = __rdmsr(MSR_AMD64_SEV);
-       feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
-
        /*
         * Check for the SME/SEV feature:
         *   CPUID Fn8000_001F[EAX]
@@ -519,11 +515,16 @@ void __init sme_enable(struct boot_params *bp)
        eax = 0x8000001f;
        ecx = 0;
        native_cpuid(&eax, &ebx, &ecx, &edx);
-       if (!(eax & feature_mask))
+       /* Check whether SEV or SME is supported */
+       if (!(eax & (AMD_SEV_BIT | AMD_SME_BIT)))
                return;
 
        me_mask = 1UL << (ebx & 0x3f);
 
+       /* Check the SEV MSR whether SEV or SME is enabled */
+       sev_status   = __rdmsr(MSR_AMD64_SEV);
+       feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
+
        /* Check if memory encryption is enabled */
        if (feature_mask == AMD_SME_BIT) {
                /*