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A malicious hypervisor could disable the CPUID intercept for an SEV or SEV-ES guest and trick it into the no-SEV boot path, where it could potentially reveal secrets. This is not an issue for SEV-SNP guests, as the CPUID intercept can't be disabled for those. Remove the Hypervisor CPUID bit check from the SEV detection code to protect against this kind of attack and add a Hypervisor bit equals zero check to the SME detection path to prevent non-encrypted guests from trying to enable SME. This handles the following cases: 1) SEV(-ES) guest where CPUID intercept is disabled. The guest will still see leaf 0x8000001f and the SEV bit. It can retrieve the C-bit and boot normally. 2) Non-encrypted guests with intercepted CPUID will check the SEV_STATUS MSR and find it 0 and will try to enable SME. This will fail when the guest finds MSR_K8_SYSCFG to be zero, as it is emulated by KVM. But we can't rely on that, as there might be other hypervisors which return this MSR with bit 23 set. The Hypervisor bit check will prevent that the guest tries to enable SME in this case. 3) Non-encrypted guests on SEV capable hosts with CPUID intercept disabled (by a malicious hypervisor) will try to boot into the SME path. This will fail, but it is also not considered a problem because non-encrypted guests have no protection against the hypervisor anyway. [ bp: s/non-SEV/non-encrypted/g ] Signed-off-by: Joerg Roedel <jroedel@suse.de> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lkml.kernel.org/r/20210312123824.306-3-joro@8bytes.org |
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| compressed | ||
| tools | ||
| .gitignore | ||
| a20.c | ||
| apm.c | ||
| bioscall.S | ||
| bitops.h | ||
| boot.h | ||
| cmdline.c | ||
| copy.S | ||
| cpu.c | ||
| cpucheck.c | ||
| cpuflags.c | ||
| cpuflags.h | ||
| ctype.h | ||
| early_serial_console.c | ||
| edd.c | ||
| genimage.sh | ||
| header.S | ||
| install.sh | ||
| main.c | ||
| Makefile | ||
| memory.c | ||
| mkcpustr.c | ||
| mtools.conf.in | ||
| pm.c | ||
| pmjump.S | ||
| printf.c | ||
| regs.c | ||
| setup.ld | ||
| string.c | ||
| string.h | ||
| tty.c | ||
| version.c | ||
| vesa.h | ||
| video-bios.c | ||
| video-mode.c | ||
| video-vesa.c | ||
| video-vga.c | ||
| video.c | ||
| video.h | ||