linux-kernel - [PATCH] KVM: x86: zero IDT limit on entry to SMM

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-next>] [day] [month] [year] [list]

Message-Id: <1438944883-3796-1-git-send-email-pbonzini@redhat.com>
Date:	Fri,  7 Aug 2015 12:54:43 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	rkrcmar@...hat.com, dgilbert@...hat.com
Subject: [PATCH] KVM: x86: zero IDT limit on entry to SMM

The recent BlackHat 2015 presentation "The Memory Sinkhole"
mentions that the IDT limit is zeroed on entry to SMM.

This is not documented, and must have changed some time after 2010
(see http://www.ssi.gouv.fr/uploads/IMG/pdf/IT_Defense_2010_final.pdf).
KVM was not doing it, but the fix is easy.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5ef2560075bf..c5e88a881899 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6327,6 +6327,7 @@ static void process_smi_save_state_64(struct kvm_vcpu *vcpu, char *buf)
 static void process_smi(struct kvm_vcpu *vcpu)
 {
 	struct kvm_segment cs, ds;
+	struct desc_ptr dt;
 	char buf[512];
 	u32 cr0;
 
@@ -6359,6 +6360,10 @@ static void process_smi(struct kvm_vcpu *vcpu)
 
 	kvm_x86_ops->set_cr4(vcpu, 0);
 
+	/* Undocumented: IDT limit is set to zero on entry to SMM.  */
+	dt.address = dt.size = 0;
+	kvm_x86_ops->set_idt(vcpu, &dt);
+
 	__kvm_set_dr(vcpu, 7, DR7_FIXED_1);
 
 	cs.selector = (vcpu->arch.smbase >> 4) & 0xffff;
-- 
1.8.3.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/