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Subject[PATCH 3.10 054/123] KVM: x86: Check non-canonical addresses upon WRMSR
Date
3.10-stable review patch.  If anyone has any objections, please let me know.

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

From: Nadav Amit <namit@cs.technion.ac.il>

commit 854e8bb1aa06c578c2c9145fa6bfe3680ef63b23 upstream.

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.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/kvm_host.h | 14 ++++++++++++++
arch/x86/kvm/svm.c | 2 +-
arch/x86/kvm/vmx.c | 2 +-
arch/x86/kvm/x86.c | 27 ++++++++++++++++++++++++++-
4 files changed, 42 insertions(+), 3 deletions(-)

--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -953,6 +953,20 @@ static inline void kvm_inject_gp(struct
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)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3196,7 +3196,7 @@ static int wrmsr_interception(struct vcp
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 {
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5065,7 +5065,7 @@ static int handle_wrmsr(struct kvm_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;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -925,7 +925,6 @@ 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.
@@ -933,8 +932,34 @@ 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



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