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KVM: Fix fs/gs reload oops with invalid ldt

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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@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Avi Kivity 2010-10-19 16:46:55 +02:00 committed by Marcelo Tosatti
parent 2b666ca4a6
commit 9581d442b9
3 changed files with 19 additions and 44 deletions
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24
arch/x86/include/asm/kvm_host.h
View File

@ -652,20 +652,6 @@ 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;
@ -673,16 +659,6 @@ 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));

15
arch/x86/kvm/svm.c
View File

@ -3163,8 +3163,8 @@ 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;
/* required for live migration with NPT */
@ -3251,10 +3251,15 @@ 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);

24
arch/x86/kvm/vmx.c
View File

@ -803,7 +803,7 @@ 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;
@ -811,7 +811,7 @@ 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 {
@ -841,27 +841,21 @@ 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
@ -2589,8 +2583,8 @@ 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);