From: Joerg Roedel <joro@8bytes.org>
To: x86@kernel.org
Cc: Joerg Roedel <joro@8bytes.org>, Joerg Roedel <jroedel@suse.de>,
hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Jiri Slaby <jslaby@suse.cz>,
Dan Williams <dan.j.williams@intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Juergen Gross <jgross@suse.com>,
Kees Cook <keescook@chromium.org>,
David Rientjes <rientjes@google.com>,
Cfir Cohen <cfir@google.com>, Erdem Aktas <erdemaktas@google.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mike Stunes <mstunes@vmware.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Martin Radev <martin.b.radev@gmail.com>,
Arvind Sankar <nivedita@alum.mit.edu>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: [PATCH 5/7] x86/boot/compressed/64: Add CPUID sanity check to 32-bit boot-path
Date: Wed, 10 Feb 2021 11:21:33 +0100 [thread overview]
Message-ID: <20210210102135.30667-6-joro@8bytes.org> (raw)
In-Reply-To: <20210210102135.30667-1-joro@8bytes.org>
From: Joerg Roedel <jroedel@suse.de>
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@suse.de>
---
arch/x86/boot/compressed/mem_encrypt.S | 36 ++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
index 350ecb56c7e4..091502cde070 100644
--- a/arch/x86/boot/compressed/mem_encrypt.S
+++ b/arch/x86/boot/compressed/mem_encrypt.S
@@ -126,6 +126,34 @@ SYM_CODE_START(startup32_vc_handler)
SEV_ES_REQ_CPUID fn=%ebx reg=3
movl %edx, (%esp)
+ /*
+ * Sanity check CPUID results from the Hypervisor. See comment in
+ * do_vc_no_ghcb() for more details on why this is necessary.
+ */
+
+ /* Fail if Hypervisor bit not set in CPUID[1].ECX[31] */
+ cmpl $1, %ebx
+ jne .Lcheck_leaf
+ btl $31, 4(%esp)
+ jnc .Lfail
+ jmp .Ldone
+
+.Lcheck_leaf:
+ /* 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
@@ -139,6 +167,14 @@ 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)
--
2.30.0
next prev parent reply other threads:[~2021-02-10 10:33 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-10 10:21 [PATCH 0/7] x86/seves: Support 32-bit boot path and other updates Joerg Roedel
2021-02-10 10:21 ` [PATCH 1/7] x86/boot/compressed/64: Cleanup exception handling before booting kernel Joerg Roedel
2021-02-10 10:21 ` [PATCH 2/7] x86/boot/compressed/64: Reload CS in startup_32 Joerg Roedel
2021-02-10 10:21 ` [PATCH 3/7] x86/boot/compressed/64: Setup IDT in startup_32 boot path Joerg Roedel
2021-02-24 10:49 ` Borislav Petkov
2021-02-10 10:21 ` [PATCH 4/7] x86/boot/compressed/64: Add 32-bit boot #VC handler Joerg Roedel
2021-02-25 12:13 ` Borislav Petkov
2021-02-10 10:21 ` Joerg Roedel [this message]
2021-02-10 10:21 ` [PATCH 6/7] x86/boot/compressed/64: Check SEV encryption in 32-bit boot-path Joerg Roedel
2021-02-10 16:25 ` Dave Hansen
2021-02-10 16:46 ` Joerg Roedel
2021-02-10 16:47 ` Dave Hansen
2021-02-10 20:44 ` Tom Lendacky
2021-03-02 19:43 ` Borislav Petkov
2021-03-09 10:02 ` Joerg Roedel
2021-02-10 10:21 ` [PATCH 7/7] x86/sev-es: Replace open-coded hlt-loops with sev_es_terminate() Joerg Roedel
2021-02-10 14:58 ` [PATCH 0/7] x86/seves: Support 32-bit boot path and other updates Konrad Rzeszutek Wilk
2021-02-10 15:12 ` Joerg Roedel
2021-02-10 15:19 ` Konrad Rzeszutek Wilk
2021-02-10 15:27 ` Joerg Roedel
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