linux-kernel - [PATCH v2 2/3] kvm, vmx: move register clearing out of assembly path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <33085f6c98496ed8094ce68855b49851abb86406.1540822350.git.jsteckli@amazon.de>
Date:   Mon, 29 Oct 2018 16:40:43 +0100
From:   Julian Stecklina <jsteckli@...zon.de>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Julian Stecklina <jsteckli@...zon.de>,
        Julian Stecklina <js@...en8.de>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] kvm, vmx: move register clearing out of assembly path

Split the security related register clearing out of the large inline
assembly VM entry path. This results in two slightly less complicated
inline assembly statements, where it is clearer what each one does.

Signed-off-by: Julian Stecklina <jsteckli@...zon.de>
Reviewed-by: Jan H. Schönherr <jschoenh@...zon.de>
Reviewed-by: Konrad Jan Miller <kjm@...zon.de>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/kvm/vmx.c | 45 ++++++++++++++++++++++++++++-----------------
 1 file changed, 28 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a6e5a5c..29a2ee7 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11281,24 +11281,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 		"mov %%r13, %c[r13](%0) \n\t"
 		"mov %%r14, %c[r14](%0) \n\t"
 		"mov %%r15, %c[r15](%0) \n\t"
-		/*
-		* Clear host registers marked as clobbered to prevent
-		* speculative use.
-		*/
-		"xor %%r8d,  %%r8d \n\t"
-		"xor %%r9d,  %%r9d \n\t"
-		"xor %%r10d, %%r10d \n\t"
-		"xor %%r11d, %%r11d \n\t"
-		"xor %%r12d, %%r12d \n\t"
-		"xor %%r13d, %%r13d \n\t"
-		"xor %%r14d, %%r14d \n\t"
-		"xor %%r15d, %%r15d \n\t"
 #endif
-
-		"xor %%eax, %%eax \n\t"
-		"xor %%ebx, %%ebx \n\t"
-		"xor %%esi, %%esi \n\t"
-		"xor %%edi, %%edi \n\t"
 		"pop  %%" _ASM_BP "; pop  %%" _ASM_DX " \n\t"
 		".pushsection .rodata \n\t"
 		".global vmx_return \n\t"
@@ -11336,6 +11319,34 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	      );
 
 	/*
+	 * Don't let guest register values survive. Registers that cannot
+	 * contain guest values anymore are not touched.
+	 */
+	asm volatile (
+		"xor %%eax, %%eax \n\t"
+		"xor %%ebx, %%ebx \n\t"
+		"xor %%esi, %%esi \n\t"
+		"xor %%edi, %%edi \n\t"
+#ifdef CONFIG_X86_64
+		"xor %%r8d,  %%r8d \n\t"
+		"xor %%r9d,  %%r9d \n\t"
+		"xor %%r10d, %%r10d \n\t"
+		"xor %%r11d, %%r11d \n\t"
+		"xor %%r12d, %%r12d \n\t"
+		"xor %%r13d, %%r13d \n\t"
+		"xor %%r14d, %%r14d \n\t"
+		"xor %%r15d, %%r15d \n\t"
+#endif
+		::: "cc"
+#ifdef CONFIG_X86_64
+		 , "rax", "rbx", "rsi", "rdi"
+		 , "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
+#else
+		 , "eax", "ebx", "esi", "edi"
+#endif
+		);
+
+	/*
 	 * We do not use IBRS in the kernel. If this vCPU has used the
 	 * SPEC_CTRL MSR it may have left it on; save the value and
 	 * turn it off. This is much more efficient than blindly adding
-- 
2.7.4