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KVM: x86: Check non-canonical addresses upon WRMSR

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Upon WRMSR, the CPU should inject #GP if a non-canonical value (address) is
written to certain MSRs. The behavior is "almost" identical for AMD and Intel
(ignoring MSRs that are not implemented in either architecture since they would
anyhow #GP). However, IA32_SYSENTER_ESP and IA32_SYSENTER_EIP cause #GP if
non-canonical address is written on Intel but not on AMD (which ignores the top
32-bits).

Accordingly, this patch injects a #GP on the MSRs which behave identically on
Intel and AMD.  To eliminate the differences between the architecutres, the
value which is written to IA32_SYSENTER_ESP and IA32_SYSENTER_EIP is turned to
canonical value before writing instead of injecting a #GP.

Some references from Intel and AMD manuals:

According to Intel SDM description of WRMSR instruction #GP is expected on
WRMSR "If the source register contains a non-canonical address and ECX
specifies one of the following MSRs: IA32_DS_AREA, IA32_FS_BASE, IA32_GS_BASE,
IA32_KERNEL_GS_BASE, IA32_LSTAR, IA32_SYSENTER_EIP, IA32_SYSENTER_ESP."

According to AMD manual instruction manual:
LSTAR/CSTAR (SYSCALL): "The WRMSR instruction loads the target RIP into the
LSTAR and CSTAR registers.  If an RIP written by WRMSR is not in canonical
form, a general-protection exception (#GP) occurs."
IA32_GS_BASE and IA32_FS_BASE (WRFSBASE/WRGSBASE): "The address written to the
base field must be in canonical form or a #GP fault will occur."
IA32_KERNEL_GS_BASE (SWAPGS): "The address stored in the KernelGSbase MSR must
be in canonical form."

This patch fixes CVE-2014-3610.

Cc: stable@vger.kernel.org
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Nadav Amit 2014-09-16 03:24:05 +03:00 committed by Paolo Bonzini
parent c3351dfabf
commit 854e8bb1aa
4 changed files with 42 additions and 3 deletions
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14
arch/x86/include/asm/kvm_host.h
View File

@ -989,6 +989,20 @@ static inline void kvm_inject_gp(struct kvm_vcpu *vcpu, u32 error_code)
kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
}
static inline u64 get_canonical(u64 la)
{
return ((int64_t)la << 16) >> 16;
}
static inline bool is_noncanonical_address(u64 la)
{
#ifdef CONFIG_X86_64
return get_canonical(la) != la;
#else
return false;
#endif
}
#define TSS_IOPB_BASE_OFFSET 0x66
#define TSS_BASE_SIZE 0x68
#define TSS_IOPB_SIZE (65536 / 8)

2
arch/x86/kvm/svm.c
View File

@ -3251,7 +3251,7 @@ static int wrmsr_interception(struct vcpu_svm *svm)
msr.host_initiated = false;
svm->next_rip = kvm_rip_read(&svm->vcpu) + 2;
if (svm_set_msr(&svm->vcpu, &msr)) {
if (kvm_set_msr(&svm->vcpu, &msr)) {
trace_kvm_msr_write_ex(ecx, data);
kvm_inject_gp(&svm->vcpu, 0);
} else {

2
arch/x86/kvm/vmx.c
View File

@ -5291,7 +5291,7 @@ static int handle_wrmsr(struct kvm_vcpu *vcpu)
msr.data = data;
msr.index = ecx;
msr.host_initiated = false;
if (vmx_set_msr(vcpu, &msr) != 0) {
if (kvm_set_msr(vcpu, &msr) != 0) {
trace_kvm_msr_write_ex(ecx, data);
kvm_inject_gp(vcpu, 0);
return 1;

27
arch/x86/kvm/x86.c
View File

@ -987,7 +987,6 @@ void kvm_enable_efer_bits(u64 mask)
}
EXPORT_SYMBOL_GPL(kvm_enable_efer_bits);
/*
* Writes msr value into into the appropriate "register".
* Returns 0 on success, non-0 otherwise.
@ -995,8 +994,34 @@ EXPORT_SYMBOL_GPL(kvm_enable_efer_bits);
*/
int kvm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
{
switch (msr->index) {
case MSR_FS_BASE:
case MSR_GS_BASE:
case MSR_KERNEL_GS_BASE:
case MSR_CSTAR:
case MSR_LSTAR:
if (is_noncanonical_address(msr->data))
return 1;
break;
case MSR_IA32_SYSENTER_EIP:
case MSR_IA32_SYSENTER_ESP:
/*
* IA32_SYSENTER_ESP and IA32_SYSENTER_EIP cause #GP if
* non-canonical address is written on Intel but not on
* AMD (which ignores the top 32-bits, because it does
* not implement 64-bit SYSENTER).
*
* 64-bit code should hence be able to write a non-canonical
* value on AMD. Making the address canonical ensures that
* vmentry does not fail on Intel after writing a non-canonical
* value, and that something deterministic happens if the guest
* invokes 64-bit SYSENTER.
*/
msr->data = get_canonical(msr->data);
}
return kvm_x86_ops->set_msr(vcpu, msr);
}
EXPORT_SYMBOL_GPL(kvm_set_msr);
/*
* Adapt set_msr() to msr_io()'s calling convention