From: Nadav Amit Date: Fri, 24 Oct 2014 17:07:12 +0200 Subject: [PATCH] KVM: x86: Check non-canonical addresses upon WRMSR 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 Signed-off-by: Paolo Bonzini --- 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(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 7d603a71ab3a..ccc94de4ac49 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -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) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 65510f624dfe..00bed2c5e948 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -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 { diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 0acac81f198b..148020a7dd98 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -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; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 34c8f94331f8..5a7195573a32 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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 -- 1.9.3