kvm reloads the host's fs and gs blindly, however the underlying segment
descriptors may be invalid due to the user modifying the ldt after loading
them.
Fix by using the safe accessors (loadsegment() and load_gs_index()) instead
of home grown unsafe versions.
This is CVE-2010-3698.
KVM-Stable-Tag.
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 24 ------------------------
arch/x86/kvm/svm.c | 15 ++++++++++-----
arch/x86/kvm/vmx.c | 24 +++++++++---------------
3 files changed, 19 insertions(+), 44 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d2fa951..1be0058 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -732,20 +732,6 @@ static inline struct kvm_mmu_page *page_header(hpa_t shadow_page)
return (struct kvm_mmu_page *)page_private(page);
}
-static inline u16 kvm_read_fs(void)
-{
- u16 seg;
- asm("mov %%fs, %0" : "=g"(seg));
- return seg;
-}
-
-static inline u16 kvm_read_gs(void)
-{
- u16 seg;
- asm("mov %%gs, %0" : "=g"(seg));
- return seg;
-}
-
static inline u16 kvm_read_ldt(void)
{
u16 ldt;
@@ -753,16 +739,6 @@ static inline u16 kvm_read_ldt(void)
return ldt;
}
-static inline void kvm_load_fs(u16 sel)
-{
- asm("mov %0, %%fs" : : "rm"(sel));
-}
-
-static inline void kvm_load_gs(u16 sel)
-{
- asm("mov %0, %%gs" : : "rm"(sel));
-}
-
static inline void kvm_load_ldt(u16 sel)
{
asm("lldt %0" : : "rm"(sel));
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 9fa27a5..f931a28 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3332,8 +3332,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
sync_lapic_to_cr8(vcpu);
save_host_msrs(vcpu);
- fs_selector = kvm_read_fs();
- gs_selector = kvm_read_gs();
+ savesegment(fs, fs_selector);
+ savesegment(gs, gs_selector);
ldt_selector = kvm_read_ldt();
svm->vmcb->save.cr2 = vcpu->arch.cr2;
@@ -3417,10 +3417,15 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
vcpu->arch.regs[VCPU_REGS_RSP] = svm->vmcb->save.rsp;
vcpu->arch.regs[VCPU_REGS_RIP] = svm->vmcb->save.rip;
- kvm_load_fs(fs_selector);
- kvm_load_gs(gs_selector);
- kvm_load_ldt(ldt_selector);
load_host_msrs(vcpu);
+ loadsegment(fs, fs_selector);
+#ifdef CONFIG_X86_64
+ load_gs_index(gs_selector);
+ wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gs);
+#else
+ loadsegment(gs, gs_selector);
+#endif
+ kvm_load_ldt(ldt_selector);
reload_tss(vcpu);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c6b872f..8da0e45 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -796,7 +796,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
*/
vmx->host_state.ldt_sel = kvm_read_ldt();
vmx->host_state.gs_ldt_reload_needed = vmx->host_state.ldt_sel;
- vmx->host_state.fs_sel = kvm_read_fs();
+ savesegment(fs, vmx->host_state.fs_sel);
if (!(vmx->host_state.fs_sel & 7)) {
vmcs_write16(HOST_FS_SELECTOR, vmx->host_state.fs_sel);
vmx->host_state.fs_reload_needed = 0;
@@ -804,7 +804,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
vmcs_write16(HOST_FS_SELECTOR, 0);
vmx->host_state.fs_reload_needed = 1;
}
- vmx->host_state.gs_sel = kvm_read_gs();
+ savesegment(gs, vmx->host_state.gs_sel);
if (!(vmx->host_state.gs_sel & 7))
vmcs_write16(HOST_GS_SELECTOR, vmx->host_state.gs_sel);
else {
@@ -834,27 +834,21 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
static void __vmx_load_host_state(struct vcpu_vmx *vmx)
{
- unsigned long flags;
-
if (!vmx->host_state.loaded)
return;
++vmx->vcpu.stat.host_state_reload;
vmx->host_state.loaded = 0;
if (vmx->host_state.fs_reload_needed)
- kvm_load_fs(vmx->host_state.fs_sel);
+ loadsegment(fs, vmx->host_state.fs_sel);
if (vmx->host_state.gs_ldt_reload_needed) {
kvm_load_ldt(vmx->host_state.ldt_sel);
- /*
- * If we have to reload gs, we must take care to
- * preserve our gs base.
- */
- local_irq_save(flags);
- kvm_load_gs(vmx->host_state.gs_sel);
#ifdef CONFIG_X86_64
- wrmsrl(MSR_GS_BASE, vmcs_readl(HOST_GS_BASE));
+ 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
- local_irq_restore(flags);
}
reload_tss();
#ifdef CONFIG_X86_64
@@ -2563,8 +2557,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmcs_write16(HOST_CS_SELECTOR, __KERNEL_CS); /* 22.2.4 */
vmcs_write16(HOST_DS_SELECTOR, __KERNEL_DS); /* 22.2.4 */
vmcs_write16(HOST_ES_SELECTOR, __KERNEL_DS); /* 22.2.4 */
- vmcs_write16(HOST_FS_SELECTOR, kvm_read_fs()); /* 22.2.4 */
- vmcs_write16(HOST_GS_SELECTOR, kvm_read_gs()); /* 22.2.4 */
+ vmcs_write16(HOST_FS_SELECTOR, 0); /* 22.2.4 */
+ vmcs_write16(HOST_GS_SELECTOR, 0); /* 22.2.4 */
vmcs_write16(HOST_SS_SELECTOR, __KERNEL_DS); /* 22.2.4 */
#ifdef CONFIG_X86_64
rdmsrl(MSR_FS_BASE, a);
--
1.7.3.1
--
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