linux-kernel - [PATCH 3.2 037/104] kvm: vmx: Scrub hardware GPRs at VM-exit

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Message-ID: <lsq.1520823814.174970866@decadent.org.uk>
Date:   Mon, 12 Mar 2018 03:03:34 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Andrew Honig" <ahonig@...gle.com>,
        "Benjamin Serebrin" <serebrin@...gle.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Eric Northup" <digitaleric@...gle.com>,
        "Jim Mattson" <jmattson@...gle.com>
Subject: [PATCH 3.2 037/104] kvm: vmx: Scrub hardware GPRs at VM-exit

3.2.101-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jim Mattson <jmattson@...gle.com>

commit 0cb5b30698fdc8f6b4646012e3acb4ddce430788 upstream.

Guest GPR values are live in the hardware GPRs at VM-exit.  Do not
leave any guest values in hardware GPRs after the guest GPR values are
saved to the vcpu_vmx structure.

This is a partial mitigation for CVE 2017-5715 and CVE 2017-5753.
Specifically, it defeats the Project Zero PoC for CVE 2017-5715.

Suggested-by: Eric Northup <digitaleric@...gle.com>
Signed-off-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: Eric Northup <digitaleric@...gle.com>
Reviewed-by: Benjamin Serebrin <serebrin@...gle.com>
Reviewed-by: Andrew Honig <ahonig@...gle.com>
[Paolo: Add AMD bits, Signed-off-by: Tom Lendacky <thomas.lendacky@....com>]
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/svm.c | 19 +++++++++++++++++++
 arch/x86/kvm/vmx.c | 14 +++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3748,6 +3748,25 @@ static void svm_vcpu_run(struct kvm_vcpu
 		"mov %%r14, %c[r14](%[svm]) \n\t"
 		"mov %%r15, %c[r15](%[svm]) \n\t"
 #endif
+		/*
+		* Clear host registers marked as clobbered to prevent
+		* speculative use.
+		*/
+		"xor %%" _ASM_BX ", %%" _ASM_BX " \n\t"
+		"xor %%" _ASM_CX ", %%" _ASM_CX " \n\t"
+		"xor %%" _ASM_DX ", %%" _ASM_DX " \n\t"
+		"xor %%" _ASM_SI ", %%" _ASM_SI " \n\t"
+		"xor %%" _ASM_DI ", %%" _ASM_DI " \n\t"
+#ifdef CONFIG_X86_64
+		"xor %%r8, %%r8 \n\t"
+		"xor %%r9, %%r9 \n\t"
+		"xor %%r10, %%r10 \n\t"
+		"xor %%r11, %%r11 \n\t"
+		"xor %%r12, %%r12 \n\t"
+		"xor %%r13, %%r13 \n\t"
+		"xor %%r14, %%r14 \n\t"
+		"xor %%r15, %%r15 \n\t"
+#endif
 		"pop %%" _ASM_BP
 		:
 		: [svm]"a"(svm),
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6228,6 +6228,7 @@ static void __noclone vmx_vcpu_run(struc
 		/* Save guest registers, load host registers, keep flags */
 		"mov %0, %c[wordsize](%%" _ASM_SP ") \n\t"
 		"pop %0 \n\t"
+		"setbe %c[fail](%0)\n\t"
 		"mov %%" _ASM_AX ", %c[rax](%0) \n\t"
 		"mov %%" _ASM_BX ", %c[rbx](%0) \n\t"
 		__ASM_SIZE(pop) " %c[rcx](%0) \n\t"
@@ -6244,12 +6245,23 @@ static void __noclone vmx_vcpu_run(struc
 		"mov %%r13, %c[r13](%0) \n\t"
 		"mov %%r14, %c[r14](%0) \n\t"
 		"mov %%r15, %c[r15](%0) \n\t"
+		"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
 		"mov %%cr2, %%" _ASM_AX "   \n\t"
 		"mov %%" _ASM_AX ", %c[cr2](%0) \n\t"
 
+		"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"
-		"setbe %c[fail](%0) \n\t"
 	      : : "c"(vmx), "d"((unsigned long)HOST_RSP),
 		[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
 		[fail]"i"(offsetof(struct vcpu_vmx, fail)),