From: Borislav Petkov (AMD) bp@alien8.de
commit bee6cf1a80b54548a039e224c651bb15b644a480 upstream.
Tao Liu reported a boot hang on an Intel Atom machine due to an unmapped EFI config table. The reason being that the CC blob which contains the CPUID page for AMD SNP guests is parsed for before even checking whether the machine runs on AMD hardware.
Usually that's not a problem on !AMD hw - it simply won't find the CC blob's GUID and return. However, if any parts of the config table pointers array is not mapped, the kernel will #PF very early in the decompressor stage without any opportunity to recover.
Therefore, do a superficial CPUID check before poking for the CC blob. This will fix the current issue on real hardware. It would also work as a guest on a non-lying hypervisor.
For the lying hypervisor, the check is done again, *after* parsing the CC blob as the real CPUID page will be present then.
Clear the #VC handler in case SEV-{ES,SNP} hasn't been detected, as a precaution.
Fixes: c01fce9cef84 ("x86/compressed: Add SEV-SNP feature detection/setup") Reported-by: Tao Liu ltao@redhat.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Acked-by: Tom Lendacky thomas.lendacky@amd.com Tested-by: Tao Liu ltao@redhat.com Cc: stable@kernel.org Link: https://lore.kernel.org/r/20230601072043.24439-1-ltao@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/boot/compressed/idt_64.c | 9 ++++++++- arch/x86/boot/compressed/sev.c | 37 +++++++++++++++++++++++++++++++++++-- 2 files changed, 43 insertions(+), 3 deletions(-)
--- a/arch/x86/boot/compressed/idt_64.c +++ b/arch/x86/boot/compressed/idt_64.c @@ -63,7 +63,14 @@ void load_stage2_idt(void) set_idt_entry(X86_TRAP_PF, boot_page_fault);
#ifdef CONFIG_AMD_MEM_ENCRYPT - set_idt_entry(X86_TRAP_VC, boot_stage2_vc); + /* + * Clear the second stage #VC handler in case guest types + * needing #VC have not been detected. + */ + if (sev_status & BIT(1)) + set_idt_entry(X86_TRAP_VC, boot_stage2_vc); + else + set_idt_entry(X86_TRAP_VC, NULL); #endif
load_boot_idt(&boot_idt_desc); --- a/arch/x86/boot/compressed/sev.c +++ b/arch/x86/boot/compressed/sev.c @@ -353,12 +353,45 @@ void sev_enable(struct boot_params *bp) bp->cc_blob_address = 0;
/* + * Do an initial SEV capability check before snp_init() which + * loads the CPUID page and the same checks afterwards are done + * without the hypervisor and are trustworthy. + * + * If the HV fakes SEV support, the guest will crash'n'burn + * which is good enough. + */ + + /* Check for the SME/SEV support leaf */ + eax = 0x80000000; + ecx = 0; + native_cpuid(&eax, &ebx, &ecx, &edx); + if (eax < 0x8000001f) + return; + + /* + * Check for the SME/SEV feature: + * CPUID Fn8000_001F[EAX] + * - Bit 0 - Secure Memory Encryption support + * - Bit 1 - Secure Encrypted Virtualization support + * CPUID Fn8000_001F[EBX] + * - Bits 5:0 - Pagetable bit position used to indicate encryption + */ + eax = 0x8000001f; + ecx = 0; + native_cpuid(&eax, &ebx, &ecx, &edx); + /* Check whether SEV is supported */ + if (!(eax & BIT(1))) + return; + + /* * Setup/preliminary detection of SNP. This will be sanity-checked * against CPUID/MSR values later. */ snp = snp_init(bp);
- /* Check for the SME/SEV support leaf */ + /* Now repeat the checks with the SNP CPUID table. */ + + /* Recheck the SME/SEV support leaf */ eax = 0x80000000; ecx = 0; native_cpuid(&eax, &ebx, &ecx, &edx); @@ -366,7 +399,7 @@ void sev_enable(struct boot_params *bp) return;
/* - * Check for the SME/SEV feature: + * Recheck for the SME/SEV feature: * CPUID Fn8000_001F[EAX] * - Bit 0 - Secure Memory Encryption support * - Bit 1 - Secure Encrypted Virtualization support