Re: [Xen-devel] [PATCH 1/2] x86/hvm: Don't raise #GP behind the emulators back for CR accesses

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: 02 March 2017 15:00
> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
> <JBeulich@xxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Jun
> Nakajima <jun.nakajima@xxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>;
> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>; Suravee Suthikulpanit
> <suravee.suthikulpanit@xxxxxxx>
> Subject: [PATCH 1/2] x86/hvm: Don't raise #GP behind the emulators back
> for CR accesses
> 
> hvm_set_cr{0,4}() are reachable from the emulator, but use
> hvm_inject_hw_exception() directly.
> 
> Alter the API to make the callers of hvm_set_cr{0,3,4}() responsible for
> raising #GP, and apply this change to all existing callers.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

emulate code...

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> 
> Issues identified which I am purposefully not fixing in this patch:
> 
> (I will try to get around to them, but probably not in the 4.9 timeframe, at
> this point.)
> 
>  * hvm_set_cr3() doesn't handle bad 32bit PAE PDPTRs properly, as it doesn't
>    actually have a path which raises #GP.
>  * There is a lot of redundancy in our HVM CR setting routines, but not
> enough
>    to trivially dedup at this point.
>  * Both nested VT-x and SVM are liable raise #GP with L1, rather than failing
>    the virtual vmentry/vmexit.  This is not a change in behaviour, but is far
>    more obvious now.
>  * The hvm_do_resume() path for vm_event processing has the same bug as
> the
>    MSR side, where exceptions are raised after %rip has moved forwards.  This
>    is also not a change in behaviour.
> ---
>  xen/arch/x86/hvm/emulate.c        | 24 ++++++++++++----
>  xen/arch/x86/hvm/hvm.c            | 59 ++++++++++++++++++++++--------------
> ---
>  xen/arch/x86/hvm/svm/nestedsvm.c  | 14 ++++++++++
>  xen/arch/x86/hvm/vmx/vmx.c        |  7 ++++-
>  xen/arch/x86/hvm/vmx/vvmx.c       | 29 +++++++++++++++----
>  xen/include/asm-x86/hvm/support.h |  6 +++-
>  6 files changed, 101 insertions(+), 38 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
> index 93782d0..1c66010 100644
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -1520,23 +1520,37 @@ static int hvmemul_write_cr(
>      unsigned long val,
>      struct x86_emulate_ctxt *ctxt)
>  {
> +    int rc;
> +
>      HVMTRACE_LONG_2D(CR_WRITE, reg, TRC_PAR_LONG(val));
>      switch ( reg )
>      {
>      case 0:
> -        return hvm_set_cr0(val, 1);
> +        rc = hvm_set_cr0(val, 1);
> +        break;
> +
>      case 2:
>          current->arch.hvm_vcpu.guest_cr[2] = val;
> -        return X86EMUL_OKAY;
> +        rc = X86EMUL_OKAY;
> +        break;
> +
>      case 3:
> -        return hvm_set_cr3(val, 1);
> +        rc = hvm_set_cr3(val, 1);
> +        break;
> +
>      case 4:
> -        return hvm_set_cr4(val, 1);
> +        rc = hvm_set_cr4(val, 1);
> +        break;
> +
>      default:
> +        rc = X86EMUL_UNHANDLEABLE;
>          break;
>      }
> 
> -    return X86EMUL_UNHANDLEABLE;
> +    if ( rc == X86EMUL_EXCEPTION )
> +        x86_emul_hw_exception(TRAP_gp_fault, 0, ctxt);
> +
> +    return rc;
>  }
> 
>  static int hvmemul_read_msr(
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 7432c70..ccfae4f 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -527,19 +527,25 @@ void hvm_do_resume(struct vcpu *v)
> 
>          if ( w->do_write.cr0 )
>          {
> -            hvm_set_cr0(w->cr0, 0);
> +            if ( hvm_set_cr0(w->cr0, 0) == X86EMUL_EXCEPTION )
> +                hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
>              w->do_write.cr0 = 0;
>          }
> 
>          if ( w->do_write.cr4 )
>          {
> -            hvm_set_cr4(w->cr4, 0);
> +            if ( hvm_set_cr4(w->cr4, 0) == X86EMUL_EXCEPTION )
> +                hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
>              w->do_write.cr4 = 0;
>          }
> 
>          if ( w->do_write.cr3 )
>          {
> -            hvm_set_cr3(w->cr3, 0);
> +            if ( hvm_set_cr3(w->cr3, 0) == X86EMUL_EXCEPTION )
> +                hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
>              w->do_write.cr3 = 0;
>          }
>      }
> @@ -2068,6 +2074,7 @@ int hvm_mov_to_cr(unsigned int cr, unsigned int
> gpr)
>  {
>      struct vcpu *curr = current;
>      unsigned long val, *reg;
> +    int rc;
> 
>      if ( (reg = decode_register(gpr, guest_cpu_user_regs(), 0)) == NULL )
>      {
> @@ -2082,16 +2089,20 @@ int hvm_mov_to_cr(unsigned int cr, unsigned int
> gpr)
>      switch ( cr )
>      {
>      case 0:
> -        return hvm_set_cr0(val, 1);
> +        rc = hvm_set_cr0(val, 1);
> +        break;
> 
>      case 3:
> -        return hvm_set_cr3(val, 1);
> +        rc = hvm_set_cr3(val, 1);
> +        break;
> 
>      case 4:
> -        return hvm_set_cr4(val, 1);
> +        rc = hvm_set_cr4(val, 1);
> +        break;
> 
>      case 8:
>          vlapic_set_reg(vcpu_vlapic(curr), APIC_TASKPRI, ((val & 0x0f) << 4));
> +        rc = X86EMUL_OKAY;
>          break;
> 
>      default:
> @@ -2099,7 +2110,10 @@ int hvm_mov_to_cr(unsigned int cr, unsigned int
> gpr)
>          goto exit_and_crash;
>      }
> 
> -    return X86EMUL_OKAY;
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
> +    return rc;
> 
>   exit_and_crash:
>      domain_crash(curr->domain);
> @@ -2199,7 +2213,7 @@ int hvm_set_cr0(unsigned long value, bool_t
> may_defer)
>          HVM_DBG_LOG(DBG_LEVEL_1,
>                      "Guest attempts to set upper 32 bits in CR0: %lx",
>                      value);
> -        goto gpf;
> +        return X86EMUL_EXCEPTION;
>      }
> 
>      value &= ~HVM_CR0_GUEST_RESERVED_BITS;
> @@ -2209,7 +2223,7 @@ int hvm_set_cr0(unsigned long value, bool_t
> may_defer)
> 
>      if ( !nestedhvm_vmswitch_in_progress(v) &&
>           (value & (X86_CR0_PE | X86_CR0_PG)) == X86_CR0_PG )
> -        goto gpf;
> +        return X86EMUL_EXCEPTION;
> 
>      /* A pvh is not expected to change to real mode. */
>      if ( is_pvh_domain(d) &&
> @@ -2217,7 +2231,7 @@ int hvm_set_cr0(unsigned long value, bool_t
> may_defer)
>      {
>          printk(XENLOG_G_WARNING
>                 "PVH attempting to turn off PE/PG. CR0:%lx\n", value);
> -        goto gpf;
> +        return X86EMUL_EXCEPTION;
>      }
> 
>      if ( may_defer && unlikely(v->domain-
> >arch.monitor.write_ctrlreg_enabled &
> @@ -2243,7 +2257,7 @@ int hvm_set_cr0(unsigned long value, bool_t
> may_defer)
>                   !nestedhvm_vmswitch_in_progress(v) )
>              {
>                  HVM_DBG_LOG(DBG_LEVEL_1, "Enable paging before PAE enable");
> -                goto gpf;
> +                return X86EMUL_EXCEPTION;
>              }
>              HVM_DBG_LOG(DBG_LEVEL_1, "Enabling long mode");
>              v->arch.hvm_vcpu.guest_efer |= EFER_LMA;
> @@ -2276,7 +2290,7 @@ int hvm_set_cr0(unsigned long value, bool_t
> may_defer)
>          {
>              HVM_DBG_LOG(DBG_LEVEL_1, "Guest attempts to clear CR0.PG "
>                          "while CR4.PCIDE=1");
> -            goto gpf;
> +            return X86EMUL_EXCEPTION;
>          }
> 
>          /* When CR0.PG is cleared, LMA is cleared immediately. */
> @@ -2310,10 +2324,6 @@ int hvm_set_cr0(unsigned long value, bool_t
> may_defer)
>      }
> 
>      return X86EMUL_OKAY;
> -
> - gpf:
> -    hvm_inject_hw_exception(TRAP_gp_fault, 0);
> -    return X86EMUL_EXCEPTION;
>  }
> 
>  int hvm_set_cr3(unsigned long value, bool_t may_defer)
> @@ -2373,7 +2383,7 @@ int hvm_set_cr4(unsigned long value, bool_t
> may_defer)
>          HVM_DBG_LOG(DBG_LEVEL_1,
>                      "Guest attempts to set reserved bit in CR4: %lx",
>                      value);
> -        goto gpf;
> +        return X86EMUL_EXCEPTION;
>      }
> 
>      if ( !(value & X86_CR4_PAE) )
> @@ -2382,12 +2392,12 @@ int hvm_set_cr4(unsigned long value, bool_t
> may_defer)
>          {
>              HVM_DBG_LOG(DBG_LEVEL_1, "Guest cleared CR4.PAE while "
>                          "EFER.LMA is set");
> -            goto gpf;
> +            return X86EMUL_EXCEPTION;
>          }
>          if ( is_pvh_vcpu(v) )
>          {
>              HVM_DBG_LOG(DBG_LEVEL_1, "32-bit PVH guest cleared CR4.PAE");
> -            goto gpf;
> +            return X86EMUL_EXCEPTION;
>          }
>      }
> 
> @@ -2399,7 +2409,7 @@ int hvm_set_cr4(unsigned long value, bool_t
> may_defer)
>      {
>          HVM_DBG_LOG(DBG_LEVEL_1, "Guest attempts to change CR4.PCIDE
> from "
>                      "0 to 1 while either EFER.LMA=0 or CR3[11:0]!=000H");
> -        goto gpf;
> +        return X86EMUL_EXCEPTION;
>      }
> 
>      if ( may_defer && unlikely(v->domain-
> >arch.monitor.write_ctrlreg_enabled &
> @@ -2434,10 +2444,6 @@ int hvm_set_cr4(unsigned long value, bool_t
> may_defer)
>      }
> 
>      return X86EMUL_OKAY;
> -
> - gpf:
> -    hvm_inject_hw_exception(TRAP_gp_fault, 0);
> -    return X86EMUL_EXCEPTION;
>  }
> 
>  bool_t hvm_virtual_to_linear_addr(
> @@ -3020,7 +3026,10 @@ void hvm_task_switch(
>      if ( hvm_load_segment_selector(x86_seg_ldtr, tss.ldt, 0) )
>          goto out;
> 
> -    if ( hvm_set_cr3(tss.cr3, 1) )
> +    rc = hvm_set_cr3(tss.cr3, 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +    if ( rc != X86EMUL_OKAY )
>          goto out;
> 
>      regs->rip    = tss.eip;
> diff --git a/xen/arch/x86/hvm/svm/nestedsvm.c
> b/xen/arch/x86/hvm/svm/nestedsvm.c
> index f7b7ada..d4fc81f 100644
> --- a/xen/arch/x86/hvm/svm/nestedsvm.c
> +++ b/xen/arch/x86/hvm/svm/nestedsvm.c
> @@ -286,6 +286,8 @@ static int nsvm_vcpu_hostrestore(struct vcpu *v,
> struct cpu_user_regs *regs)
>      /* CR4 */
>      v->arch.hvm_vcpu.guest_cr[4] = n1vmcb->_cr4;
>      rc = hvm_set_cr4(n1vmcb->_cr4, 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      if (rc != X86EMUL_OKAY)
>          gdprintk(XENLOG_ERR, "hvm_set_cr4 failed, rc: %u\n", rc);
> 
> @@ -295,6 +297,8 @@ static int nsvm_vcpu_hostrestore(struct vcpu *v,
> struct cpu_user_regs *regs)
>      v->arch.hvm_vcpu.guest_cr[0] = n1vmcb->_cr0 | X86_CR0_PE;
>      n1vmcb->rflags &= ~X86_EFLAGS_VM;
>      rc = hvm_set_cr0(n1vmcb->_cr0 | X86_CR0_PE, 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      if (rc != X86EMUL_OKAY)
>          gdprintk(XENLOG_ERR, "hvm_set_cr0 failed, rc: %u\n", rc);
>      svm->ns_cr0 = v->arch.hvm_vcpu.guest_cr[0];
> @@ -321,6 +325,8 @@ static int nsvm_vcpu_hostrestore(struct vcpu *v,
> struct cpu_user_regs *regs)
>          /* hvm_set_cr3() below sets v->arch.hvm_vcpu.guest_cr[3] for us. */
>      }
>      rc = hvm_set_cr3(n1vmcb->_cr3, 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      if (rc != X86EMUL_OKAY)
>          gdprintk(XENLOG_ERR, "hvm_set_cr3 failed, rc: %u\n", rc);
> 
> @@ -548,6 +554,8 @@ static int nsvm_vmcb_prepare4vmrun(struct vcpu *v,
> struct cpu_user_regs *regs)
>      /* CR4 */
>      v->arch.hvm_vcpu.guest_cr[4] = ns_vmcb->_cr4;
>      rc = hvm_set_cr4(ns_vmcb->_cr4, 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      if (rc != X86EMUL_OKAY)
>          gdprintk(XENLOG_ERR, "hvm_set_cr4 failed, rc: %u\n", rc);
> 
> @@ -556,6 +564,8 @@ static int nsvm_vmcb_prepare4vmrun(struct vcpu *v,
> struct cpu_user_regs *regs)
>      cr0 = nestedsvm_fpu_vmentry(svm->ns_cr0, ns_vmcb, n1vmcb, n2vmcb);
>      v->arch.hvm_vcpu.guest_cr[0] = ns_vmcb->_cr0;
>      rc = hvm_set_cr0(cr0, 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      if (rc != X86EMUL_OKAY)
>          gdprintk(XENLOG_ERR, "hvm_set_cr0 failed, rc: %u\n", rc);
> 
> @@ -572,6 +582,8 @@ static int nsvm_vmcb_prepare4vmrun(struct vcpu *v,
> struct cpu_user_regs *regs)
> 
>          /* hvm_set_cr3() below sets v->arch.hvm_vcpu.guest_cr[3] for us. */
>          rc = hvm_set_cr3(ns_vmcb->_cr3, 1);
> +        if ( rc == X86EMUL_EXCEPTION )
> +            hvm_inject_hw_exception(TRAP_gp_fault, 0);
>          if (rc != X86EMUL_OKAY)
>              gdprintk(XENLOG_ERR, "hvm_set_cr3 failed, rc: %u\n", rc);
>      } else if (paging_mode_hap(v->domain)) {
> @@ -584,6 +596,8 @@ static int nsvm_vmcb_prepare4vmrun(struct vcpu *v,
> struct cpu_user_regs *regs)
>           */
>          /* hvm_set_cr3() below sets v->arch.hvm_vcpu.guest_cr[3] for us. */
>          rc = hvm_set_cr3(ns_vmcb->_cr3, 1);
> +        if ( rc == X86EMUL_EXCEPTION )
> +            hvm_inject_hw_exception(TRAP_gp_fault, 0);
>          if (rc != X86EMUL_OKAY)
>              gdprintk(XENLOG_ERR, "hvm_set_cr3 failed, rc: %u\n", rc);
>      } else {
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 5b1717d..c2cd12d 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -2459,13 +2459,18 @@ static int vmx_cr_access(unsigned long
> exit_qualification)
>      }
>      case VMX_CONTROL_REG_ACCESS_TYPE_LMSW: {
>          unsigned long value = curr->arch.hvm_vcpu.guest_cr[0];
> +        int rc;
> 
>          /* LMSW can (1) set PE; (2) set or clear MP, EM, and TS. */
>          value = (value & ~(X86_CR0_MP|X86_CR0_EM|X86_CR0_TS)) |
>                  (VMX_CONTROL_REG_ACCESS_DATA(exit_qualification) &
>                   (X86_CR0_PE|X86_CR0_MP|X86_CR0_EM|X86_CR0_TS));
>          HVMTRACE_LONG_1D(LMSW, value);
> -        return hvm_set_cr0(value, 1);
> +
> +        if ( (rc = hvm_set_cr0(value, 1)) == X86EMUL_EXCEPTION )
> +            hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
> +        return rc;
>      }
>      default:
>          BUG();
> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c
> b/xen/arch/x86/hvm/vmx/vvmx.c
> index 0aef7a7..8a486f5 100644
> --- a/xen/arch/x86/hvm/vmx/vvmx.c
> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> @@ -1046,9 +1046,18 @@ static void load_shadow_guest_state(struct vcpu
> *v)
> 
>      nvcpu->guest_cr[0] = get_vvmcs(v, CR0_READ_SHADOW);
>      nvcpu->guest_cr[4] = get_vvmcs(v, CR4_READ_SHADOW);
> -    hvm_set_cr0(get_vvmcs(v, GUEST_CR0), 1);
> -    hvm_set_cr4(get_vvmcs(v, GUEST_CR4), 1);
> -    hvm_set_cr3(get_vvmcs(v, GUEST_CR3), 1);
> +
> +    rc = hvm_set_cr0(get_vvmcs(v, GUEST_CR0), 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
> +    rc = hvm_set_cr4(get_vvmcs(v, GUEST_CR4), 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
> +    rc = hvm_set_cr3(get_vvmcs(v, GUEST_CR3), 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> 
>      control = get_vvmcs(v, VM_ENTRY_CONTROLS);
>      if ( control & VM_ENTRY_LOAD_GUEST_PAT )
> @@ -1237,9 +1246,17 @@ static void load_vvmcs_host_state(struct vcpu *v)
>          __vmwrite(vmcs_h2g_field[i].guest_field, r);
>      }
> 
> -    hvm_set_cr0(get_vvmcs(v, HOST_CR0), 1);
> -    hvm_set_cr4(get_vvmcs(v, HOST_CR4), 1);
> -    hvm_set_cr3(get_vvmcs(v, HOST_CR3), 1);
> +    rc = hvm_set_cr0(get_vvmcs(v, HOST_CR0), 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
> +    rc = hvm_set_cr4(get_vvmcs(v, HOST_CR4), 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> +
> +    rc = hvm_set_cr3(get_vvmcs(v, HOST_CR3), 1);
> +    if ( rc == X86EMUL_EXCEPTION )
> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
> 
>      control = get_vvmcs(v, VM_EXIT_CONTROLS);
>      if ( control & VM_EXIT_LOAD_HOST_PAT )
> diff --git a/xen/include/asm-x86/hvm/support.h b/xen/include/asm-
> x86/hvm/support.h
> index cb41364..632eb90 100644
> --- a/xen/include/asm-x86/hvm/support.h
> +++ b/xen/include/asm-x86/hvm/support.h
> @@ -119,7 +119,11 @@ int __must_check hvm_handle_xsetbv(u32 index,
> u64 new_bv);
> 
>  void hvm_shadow_handle_cd(struct vcpu *v, unsigned long value);
> 
> -/* These functions all return X86EMUL return codes. */
> +/*
> + * These functions all return X86EMUL return codes.  For hvm_set_*(), the
> + * caller is responsible for injecting #GP[0] if X86EMUL_EXCEPTION is
> + * returned.
> + */
>  int hvm_set_efer(uint64_t value);
>  int hvm_set_cr0(unsigned long value, bool_t may_defer);
>  int hvm_set_cr3(unsigned long value, bool_t may_defer);
> --
> 2.1.4


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