linux-kernel - [046/127] KVM: VMX: Fix host userspace gsbase corruption

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Message-Id: <20101208004428.893591835@clark.site>
Date:	Tue, 07 Dec 2010 16:43:52 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org, greg@...ah.com
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	avi@...hat.com, mtosatti@...hat.com
Subject: [046/127] KVM: VMX: Fix host userspace gsbase corruption

2.6.32-stable review patch.  If anyone has any objections, please let us know.

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

From: Ben Hutchings <ben@...adent.org.uk>

commit c8770e7ba63bb5dd8fe5f9d251275a8fa717fb78 upstream.

We now use load_gs_index() to load gs safely; unfortunately this also
changes MSR_KERNEL_GS_BASE, which we managed separately.  This resulted
in confusion and breakage running 32-bit host userspace on a 64-bit kernel.

Fix by
- saving guest MSR_KERNEL_GS_BASE before we we reload the host's gs
- doing the host save/load unconditionally, instead of only when in guest
  long mode

Things can be cleaned up further, but this is the minmal fix for now.

Signed-off-by: Avi Kivity <avi@...hat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
[bwh: Backport to 2.6.32]
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/x86/kvm/vmx.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -654,10 +654,7 @@ static void vmx_save_host_state(struct k
 #endif
 
 #ifdef CONFIG_X86_64
-	if (is_long_mode(&vmx->vcpu))
-		save_msrs(vmx->host_msrs +
-			  vmx->msr_offset_kernel_gs_base, 1);
-
+	save_msrs(vmx->host_msrs + vmx->msr_offset_kernel_gs_base, 1);
 #endif
 	load_msrs(vmx->guest_msrs, vmx->save_nmsrs);
 	load_transition_efer(vmx);
@@ -672,17 +669,26 @@ static void __vmx_load_host_state(struct
 	vmx->host_state.loaded = 0;
 	if (vmx->host_state.fs_reload_needed)
 		loadsegment(fs, vmx->host_state.fs_sel);
+#ifdef CONFIG_X86_64
+	if (is_long_mode(&vmx->vcpu))
+		save_msrs(vmx->guest_msrs + vmx->msr_offset_kernel_gs_base, 1);
+#endif
 	if (vmx->host_state.gs_ldt_reload_needed) {
 		kvm_load_ldt(vmx->host_state.ldt_sel);
 #ifdef CONFIG_X86_64
 		load_gs_index(vmx->host_state.gs_sel);
-		wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gs);
 #else
 		loadsegment(gs, vmx->host_state.gs_sel);
 #endif
 	}
 	reload_tss();
+#ifdef CONFIG_X86_64
+	save_msrs(vmx->guest_msrs, vmx->msr_offset_kernel_gs_base);
+	save_msrs(vmx->guest_msrs + vmx->msr_offset_kernel_gs_base + 1,
+		  vmx->save_nmsrs - vmx->msr_offset_kernel_gs_base - 1);
+#else
 	save_msrs(vmx->guest_msrs, vmx->save_nmsrs);
+#endif
 	load_msrs(vmx->host_msrs, vmx->save_nmsrs);
 	reload_host_efer(vmx);
 	load_gdt(&__get_cpu_var(host_gdt));


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