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Date: Wed, 26 Apr 2023 09:31:40 +0800
From: Yuan Yao <yuan.yao@...ux.intel.com>
To: Zeng Guang <guang.zeng@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
H Peter Anvin <hpa@...or.com>, kvm@...r.kernel.org,
x86@...nel.org, linux-kernel@...r.kernel.org,
Gao Chao <chao.gao@...el.com>
Subject: Re: [PATCH 4/6] KVM: x86: LASS protection on KVM emulation when LASS
enabled
On Thu, Apr 20, 2023 at 09:37:22PM +0800, Zeng Guang wrote:
> Do LASS violation check for instructions emulated by KVM. Note that for
> instructions executed in the guest directly, hardware will perform the
> check.
>
> Not all instruction emulation leads to accesses to guest linear addresses
> because 1) some instrutions like CPUID, RDMSR, don't take memory as
> operands 2) instruction fetch in most cases is already done inside the
> guest.
>
> Four cases in which kvm may access guest linear addresses are identified
> by code inspection:
> - KVM emulator uses segmented address for instruction fetches or data
> accesses.
> - For implicit data access, KVM emulator gets address to a system data
> structure(GDT/LDT/IDT/TR).
> - For VMX instruction emulation, KVM gets the address from "VM-exit
> instruction information" field in VMCS.
> - For SGX ENCLS instruction emulation, KVM gets the address from registers.
>
> LASS violation check applies to these linear address so as to enforce
> mode-based protections as hardware behaves.
>
> As exceptions, the target memory address of emulation of invlpg, branch
> and call instructions doesn't require LASS violation check.
>
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> ---
> arch/x86/kvm/emulate.c | 36 +++++++++++++++++++++++++++++++-----
> arch/x86/kvm/vmx/nested.c | 3 +++
> arch/x86/kvm/vmx/sgx.c | 2 ++
> 3 files changed, 36 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 5cc3efa0e21c..a9a022fd712e 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -687,7 +687,8 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
> struct segmented_address addr,
> unsigned *max_size, unsigned size,
> bool write, bool fetch,
> - enum x86emul_mode mode, ulong *linear)
> + enum x86emul_mode mode, ulong *linear,
> + u64 flags)
> {
> struct desc_struct desc;
> bool usable;
> @@ -695,6 +696,7 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
> u32 lim;
> u16 sel;
> u8 va_bits;
> + u64 access = fetch ? PFERR_FETCH_MASK : 0;
>
> la = seg_base(ctxt, addr.seg) + addr.ea;
> *max_size = 0;
> @@ -740,6 +742,10 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
> }
> break;
> }
> +
> + if (ctxt->ops->check_lass(ctxt, access, *linear, flags))
> + goto bad;
> +
> if (la & (insn_alignment(ctxt, size) - 1))
> return emulate_gp(ctxt, 0);
> return X86EMUL_CONTINUE;
> @@ -757,7 +763,7 @@ static int linearize(struct x86_emulate_ctxt *ctxt,
> {
> unsigned max_size;
> return __linearize(ctxt, addr, &max_size, size, write, false,
> - ctxt->mode, linear);
> + ctxt->mode, linear, 0);
> }
>
> static inline int assign_eip(struct x86_emulate_ctxt *ctxt, ulong dst)
> @@ -770,7 +776,10 @@ static inline int assign_eip(struct x86_emulate_ctxt *ctxt, ulong dst)
>
> if (ctxt->op_bytes != sizeof(unsigned long))
> addr.ea = dst & ((1UL << (ctxt->op_bytes << 3)) - 1);
> - rc = __linearize(ctxt, addr, &max_size, 1, false, true, ctxt->mode, &linear);
> +
> + /* LASS doesn't apply to address for branch and call instructions */
> + rc = __linearize(ctxt, addr, &max_size, 1, false, true, ctxt->mode,
> + &linear, KVM_X86_EMULFLAG_SKIP_LASS);
The emulator.c is common part of x86, so may more common
abstraction like permiession_check_before_paging better ?
Let's also wait other guy's input for this.
> if (rc == X86EMUL_CONTINUE)
> ctxt->_eip = addr.ea;
> return rc;
> @@ -845,6 +854,13 @@ static inline int jmp_rel(struct x86_emulate_ctxt *ctxt, int rel)
> static int linear_read_system(struct x86_emulate_ctxt *ctxt, ulong linear,
> void *data, unsigned size)
> {
> + if (ctxt->ops->check_lass(ctxt, PFERR_IMPLICIT_ACCESS, linear, 0)) {
> + ctxt->exception.vector = GP_VECTOR;
> + ctxt->exception.error_code = 0;
> + ctxt->exception.error_code_valid = true;
> + return X86EMUL_PROPAGATE_FAULT;
> + }
> +
> return ctxt->ops->read_std(ctxt, linear, data, size, &ctxt->exception, true);
> }
>
> @@ -852,6 +868,13 @@ static int linear_write_system(struct x86_emulate_ctxt *ctxt,
> ulong linear, void *data,
> unsigned int size)
> {
> + if (ctxt->ops->check_lass(ctxt, PFERR_IMPLICIT_ACCESS, linear, 0)) {
> + ctxt->exception.vector = GP_VECTOR;
> + ctxt->exception.error_code = 0;
> + ctxt->exception.error_code_valid = true;
> + return X86EMUL_PROPAGATE_FAULT;
> + }
> +
> return ctxt->ops->write_std(ctxt, linear, data, size, &ctxt->exception, true);
> }
>
> @@ -907,7 +930,7 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
> * against op_size.
> */
> rc = __linearize(ctxt, addr, &max_size, 0, false, true, ctxt->mode,
> - &linear);
> + &linear, 0);
> if (unlikely(rc != X86EMUL_CONTINUE))
> return rc;
>
> @@ -3432,8 +3455,11 @@ static int em_invlpg(struct x86_emulate_ctxt *ctxt)
> {
> int rc;
> ulong linear;
> + unsigned max_size;
>
> - rc = linearize(ctxt, ctxt->src.addr.mem, 1, false, &linear);
> + /* LASS doesn't apply to the memory address for invlpg */
> + rc = __linearize(ctxt, ctxt->src.addr.mem, &max_size, 1, false, false,
> + ctxt->mode, &linear, KVM_X86_EMULFLAG_SKIP_LASS);
> if (rc == X86EMUL_CONTINUE)
> ctxt->ops->invlpg(ctxt, linear);
> /* Disable writeback. */
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index c8ae9d0e59b3..55c88c4593a6 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4974,6 +4974,9 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
> * destination for long mode!
> */
> exn = is_noncanonical_address(*ret, vcpu);
> +
> + if (!exn)
> + exn = __vmx_check_lass(vcpu, 0, *ret, 0);
> } else {
> /*
> * When not in long mode, the virtual/linear address is
> diff --git a/arch/x86/kvm/vmx/sgx.c b/arch/x86/kvm/vmx/sgx.c
> index b12da2a6dec9..30cb5d0980be 100644
> --- a/arch/x86/kvm/vmx/sgx.c
> +++ b/arch/x86/kvm/vmx/sgx.c
> @@ -37,6 +37,8 @@ static int sgx_get_encls_gva(struct kvm_vcpu *vcpu, unsigned long offset,
> fault = true;
> } else if (likely(is_long_mode(vcpu))) {
> fault = is_noncanonical_address(*gva, vcpu);
> + if (!fault)
> + fault = __vmx_check_lass(vcpu, 0, *gva, 0);
> } else {
> *gva &= 0xffffffff;
> fault = (s.unusable) ||
> --
> 2.27.0
>
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