The following commit has been merged into the x86/seves branch of tip: Commit-ID: e927e62d8e370ebfc0d702fec22bc752249ebcef Gitweb: https://git.kernel.org/tip/e927e62d8e370ebfc0d702fec22bc752249ebcef Author: Joerg Roedel <jroedel@xxxxxxx> AuthorDate: Fri, 12 Mar 2021 13:38:22 +01:00 Committer: Borislav Petkov <bp@xxxxxxx> CommitterDate: Thu, 18 Mar 2021 23:04:12 +01:00 x86/boot/compressed/64: Add CPUID sanity check to 32-bit boot-path The 32-bit #VC handler has no GHCB and can only handle CPUID exit codes. It is needed by the early boot code to handle #VC exceptions raised in verify_cpu() and to get the position of the C-bit. But the CPUID information comes from the hypervisor which is untrusted and might return results which trick the guest into the no-SEV boot path with no C-bit set in the page-tables. All data written to memory would then be unencrypted and could leak sensitive data to the hypervisor. Add sanity checks to the 32-bit boot #VC handler to make sure the hypervisor does not pretend that SEV is not enabled. Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Link: https://lkml.kernel.org/r/20210312123824.306-7-joro@xxxxxxxxxx --- arch/x86/boot/compressed/mem_encrypt.S | 28 +++++++++++++++++++++++++- 1 file changed, 28 insertions(+) diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S index ebc4a29..c1e81a8 100644 --- a/arch/x86/boot/compressed/mem_encrypt.S +++ b/arch/x86/boot/compressed/mem_encrypt.S @@ -139,6 +139,26 @@ SYM_CODE_START(startup32_vc_handler) jnz .Lfail movl %edx, 0(%esp) # Store result + /* + * Sanity check CPUID results from the Hypervisor. See comment in + * do_vc_no_ghcb() for more details on why this is necessary. + */ + + /* Fail if SEV leaf not available in CPUID[0x80000000].EAX */ + cmpl $0x80000000, %ebx + jne .Lcheck_sev + cmpl $0x8000001f, 12(%esp) + jb .Lfail + jmp .Ldone + +.Lcheck_sev: + /* Fail if SEV bit not set in CPUID[0x8000001f].EAX[1] */ + cmpl $0x8000001f, %ebx + jne .Ldone + btl $1, 12(%esp) + jnc .Lfail + +.Ldone: popl %edx popl %ecx popl %ebx @@ -152,6 +172,14 @@ SYM_CODE_START(startup32_vc_handler) iret .Lfail: + /* Send terminate request to Hypervisor */ + movl $0x100, %eax + xorl %edx, %edx + movl $MSR_AMD64_SEV_ES_GHCB, %ecx + wrmsr + rep; vmmcall + + /* If request fails, go to hlt loop */ hlt jmp .Lfail SYM_CODE_END(startup32_vc_handler)
|