x86: introduce a new VMASSIST for architectural behaviour of iopl

The existing vIOPL interface is hard to use, and need not be.

Introduce a VMASSIST with which a guest can opt-in to having vIOPL behaviour
consistenly with native hardware.

Specifically:
 - virtual iopl updated from do_iret() hypercalls.
 - virtual iopl reported in bounce frames.
 - guest kernels assumed to be level 0 for the purpose of iopl checks.

v->arch.pv_vcpu.iopl is altered to store IOPL shifted as it would exist
eflags, for the benefit of the assembly code.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index a4f6db27500f7f35e32fcaee8571711b812a8591..9e436efcefe9cc1fb240dd54be7b9336e1897f8a 100644 (file)
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -994,7 +994,7 @@ int arch_set_info_guest(
     init_int80_direct_trap(v);
 
     /* IOPL privileges are virtualised. */
-    v->arch.pv_vcpu.iopl = (v->arch.user_regs.eflags >> 12) & 3;
+    v->arch.pv_vcpu.iopl = v->arch.user_regs.eflags & X86_EFLAGS_IOPL;
     v->arch.user_regs.eflags &= ~X86_EFLAGS_IOPL;
 
     /* Ensure real hardware interrupts are enabled. */
@@ -1735,8 +1735,10 @@ static void load_segments(struct vcpu *n)
             cs_and_mask = (unsigned short)regs->cs |
                 ((unsigned int)vcpu_info(n, evtchn_upcall_mask) << 16);
             /* Fold upcall mask into RFLAGS.IF. */
-            eflags  = regs->_eflags & ~X86_EFLAGS_IF;
+            eflags  = regs->_eflags & ~(X86_EFLAGS_IF|X86_EFLAGS_IOPL);
             eflags |= !vcpu_info(n, evtchn_upcall_mask) << 9;
+            if ( VM_ASSIST(n->domain, architectural_iopl) )
+                eflags |= n->arch.pv_vcpu.iopl;
 
             if ( !ring_1(regs) )
             {
@@ -1763,7 +1765,8 @@ static void load_segments(struct vcpu *n)
                 vcpu_info(n, evtchn_upcall_mask) = 1;
 
             regs->entry_vector |= TRAP_syscall;
-            regs->_eflags      &= 0xFFFCBEFFUL;
+            regs->_eflags      &= ~(X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT|
+                                    X86_EFLAGS_IOPL|X86_EFLAGS_TF);
             regs->ss            = FLAT_COMPAT_KERNEL_SS;
             regs->_esp          = (unsigned long)(esp-7);
             regs->cs            = FLAT_COMPAT_KERNEL_CS;
@@ -1781,8 +1784,10 @@ static void load_segments(struct vcpu *n)
             ((unsigned long)vcpu_info(n, evtchn_upcall_mask) << 32);
 
         /* Fold upcall mask into RFLAGS.IF. */
-        rflags  = regs->rflags & ~X86_EFLAGS_IF;
+        rflags  = regs->rflags & ~(X86_EFLAGS_IF|X86_EFLAGS_IOPL);
         rflags |= !vcpu_info(n, evtchn_upcall_mask) << 9;
+        if ( VM_ASSIST(n->domain, architectural_iopl) )
+            rflags |= n->arch.pv_vcpu.iopl;
 
         if ( put_user(regs->ss,            rsp- 1) |
              put_user(regs->rsp,           rsp- 2) |
@@ -1806,7 +1811,7 @@ static void load_segments(struct vcpu *n)
 
         regs->entry_vector |= TRAP_syscall;
         regs->rflags       &= ~(X86_EFLAGS_AC|X86_EFLAGS_VM|X86_EFLAGS_RF|
-                                X86_EFLAGS_NT|X86_EFLAGS_TF);
+                                X86_EFLAGS_NT|X86_EFLAGS_IOPL|X86_EFLAGS_TF);
         regs->ss            = FLAT_KERNEL_SS;
         regs->rsp           = (unsigned long)(rsp-11);
         regs->cs            = FLAT_KERNEL_CS;

diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
index 1cb9b585cd8c80e8d5ed8d852b5fec04bebf4706..5a4979677b0b7f7c17db869d6fe3db8ec16d57ba 100644 (file)
--- a/xen/arch/x86/physdev.c
+++ b/xen/arch/x86/physdev.c
@@ -529,7 +529,7 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( set_iopl.iopl > 3 )
             break;
         ret = 0;
-        curr->arch.pv_vcpu.iopl = set_iopl.iopl;
+        curr->arch.pv_vcpu.iopl = MASK_INSR(set_iopl.iopl, X86_EFLAGS_IOPL);
         break;
     }
 

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 8125c53ffff438e725cfc6f8275520cd768da14b..7861a3c366f6a9ad396de917ce2bfa54205be02d 100644 (file)
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1779,6 +1779,17 @@ static int read_gate_descriptor(unsigned int gate_sel,
     return 1;
 }
 
+/* Perform IOPL check between the vcpu's shadowed IOPL, and the assumed cpl. */
+static bool_t iopl_ok(const struct vcpu *v, const struct cpu_user_regs *regs)
+{
+    unsigned int cpl = guest_kernel_mode(v, regs) ?
+        (VM_ASSIST(v->domain, architectural_iopl) ? 0 : 1) : 3;
+
+    ASSERT((v->arch.pv_vcpu.iopl & ~X86_EFLAGS_IOPL) == 0);
+
+    return IOPL(cpl) <= v->arch.pv_vcpu.iopl;
+}
+
 /* Has the guest requested sufficient permission for this I/O access? */
 static int guest_io_okay(
     unsigned int port, unsigned int bytes,
@@ -1788,7 +1799,7 @@ static int guest_io_okay(
     int user_mode = !(v->arch.flags & TF_kernel_mode);
 #define TOGGLE_MODE() if ( user_mode ) toggle_guest_mode(v)
 
-    if ( v->arch.pv_vcpu.iopl >= (guest_kernel_mode(v, regs) ? 1 : 3) )
+    if ( iopl_ok(v, regs) )
         return 1;
 
     if ( v->arch.pv_vcpu.iobmp_limit > (port + bytes) )
@@ -2346,7 +2357,7 @@ static int emulate_privileged_op(struct cpu_user_regs *regs)
 
     case 0xfa: /* CLI */
     case 0xfb: /* STI */
-        if ( v->arch.pv_vcpu.iopl < (guest_kernel_mode(v, regs) ? 1 : 3) )
+        if ( !iopl_ok(v, regs) )
             goto fail;
         /*
          * This is just too dangerous to allow, in my opinion. Consider if the

diff --git a/xen/arch/x86/x86_64/asm-offsets.c b/xen/arch/x86/x86_64/asm-offsets.c
index 447c650b1acedf43cd242a41f3be8c7a88e4104c..fa37ee019eff8438309fa04cf31ad3312ce1d825 100644 (file)
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -86,6 +86,7 @@ void __dummy__(void)
     OFFSET(VCPU_trap_ctxt, struct vcpu, arch.pv_vcpu.trap_ctxt);
     OFFSET(VCPU_kernel_sp, struct vcpu, arch.pv_vcpu.kernel_sp);
     OFFSET(VCPU_kernel_ss, struct vcpu, arch.pv_vcpu.kernel_ss);
+    OFFSET(VCPU_iopl, struct vcpu, arch.pv_vcpu.iopl);
     OFFSET(VCPU_guest_context_flags, struct vcpu, arch.vgc_flags);
     OFFSET(VCPU_nmi_pending, struct vcpu, nmi_pending);
     OFFSET(VCPU_mce_pending, struct vcpu, mce_pending);
@@ -166,4 +167,6 @@ void __dummy__(void)
     OFFSET(MB_flags, multiboot_info_t, flags);
     OFFSET(MB_cmdline, multiboot_info_t, cmdline);
     OFFSET(MB_mem_lower, multiboot_info_t, mem_lower);
+
+    OFFSET(DOMAIN_vm_assist, struct domain, vm_assist);
 }

diff --git a/xen/arch/x86/x86_64/compat/entry.S b/xen/arch/x86/x86_64/compat/entry.S
index fd25e84274f201a76cf902c8f6f66066d38185d2..0ff6818856edf3bbf658e3d4df4a5da34e2fd0be 100644 (file)
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -263,6 +263,7 @@ compat_create_bounce_frame:
         movl  UREGS_rsp+8(%rsp),%esi
 .Lft4:  mov   UREGS_ss+8(%rsp),%fs
 2:
+        movq  VCPU_domain(%rbx),%r8
         subl  $3*4,%esi
         movq  VCPU_vcpu_info(%rbx),%rax
         pushq COMPAT_VCPUINFO_upcall_mask(%rax)
@@ -277,9 +278,13 @@ compat_create_bounce_frame:
         testb %al,%al                   # Bits 0-7: saved_upcall_mask
         setz  %ch                       # %ch == !saved_upcall_mask
         movl  UREGS_eflags+8(%rsp),%eax
-        andl  $~X86_EFLAGS_IF,%eax
+        andl  $~(X86_EFLAGS_IF|X86_EFLAGS_IOPL),%eax
         addb  %ch,%ch                   # Bit 9 (EFLAGS.IF)
         orb   %ch,%ah                   # Fold EFLAGS.IF into %eax
+        xorl  %ecx,%ecx                 # if ( VM_ASSIST(v->domain, architectural_iopl) )
+        testb $1 << VMASST_TYPE_architectural_iopl,DOMAIN_vm_assist(%r8)
+        cmovnzl VCPU_iopl(%rbx),%ecx    # Bits 13:12 (EFLAGS.IOPL)
+        orl   %ecx,%eax                 # Fold EFLAGS.IOPL into %eax
 .Lft6:  movl  %eax,%fs:2*4(%rsi)        # EFLAGS
         movl  UREGS_rip+8(%rsp),%eax
 .Lft7:  movl  %eax,%fs:(%rsi)           # EIP

diff --git a/xen/arch/x86/x86_64/compat/traps.c b/xen/arch/x86/x86_64/compat/traps.c
index bbf18e43dedc600ba4f1442dfce114693d49774d..a6afb2612745824348a0cbd809f2b21d539314eb 100644 (file)
--- a/xen/arch/x86/x86_64/compat/traps.c
+++ b/xen/arch/x86/x86_64/compat/traps.c
@@ -99,6 +99,10 @@ unsigned int compat_iret(void)
         domain_crash(v->domain);
         return 0;
     }
+
+    if ( VM_ASSIST(v->domain, architectural_iopl) )
+        v->arch.pv_vcpu.iopl = eflags & X86_EFLAGS_IOPL;
+
     regs->_eflags = (eflags & ~X86_EFLAGS_IOPL) | X86_EFLAGS_IF;
 
     if ( unlikely(eflags & X86_EFLAGS_VM) )

diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index b0e72577de0bac53a5369ff6bf5532d6a8d42fdf..6866e8f2215f4a49dfe13b9828f7980da61057dd 100644 (file)
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -346,6 +346,7 @@ __UNLIKELY_END(create_bounce_frame_bad_sp)
         subq  $40,%rsi
         movq  UREGS_ss+8(%rsp),%rax
         ASM_STAC
+        movq  VCPU_domain(%rbx),%rdi
 .Lft2:  movq  %rax,32(%rsi)             # SS
         movq  UREGS_rsp+8(%rsp),%rax
 .Lft3:  movq  %rax,24(%rsi)             # RSP
@@ -362,9 +363,13 @@ __UNLIKELY_END(create_bounce_frame_bad_sp)
         testb $0xFF,%al                 # Bits 0-7: saved_upcall_mask
         setz  %ch                       # %ch == !saved_upcall_mask
         movl  UREGS_eflags+8(%rsp),%eax
-        andl  $~X86_EFLAGS_IF,%eax
+        andl  $~(X86_EFLAGS_IF|X86_EFLAGS_IOPL),%eax
         addb  %ch,%ch                   # Bit 9 (EFLAGS.IF)
         orb   %ch,%ah                   # Fold EFLAGS.IF into %eax
+        xorl  %ecx,%ecx                 # if ( VM_ASSIST(v->domain, architectural_iopl) )
+        testb $1 << VMASST_TYPE_architectural_iopl,DOMAIN_vm_assist(%rdi)
+        cmovnzl VCPU_iopl(%rbx),%ecx    # Bits 13:12 (EFLAGS.IOPL)
+        orl   %ecx,%eax                 # Fold EFLAGS.IOPL into %eax
 .Lft5:  movq  %rax,16(%rsi)             # RFLAGS
         movq  UREGS_rip+8(%rsp),%rax
 .Lft6:  movq  %rax,(%rsi)               # RIP

diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index 26e2dd72e6a15c3040e88c4209d5c5a40bee7093..19f58a10cc70276bb85c0d3a150c0a4d43d4ff76 100644 (file)
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -310,6 +310,9 @@ unsigned long do_iret(void)
         toggle_guest_mode(v);
     }
 
+    if ( VM_ASSIST(v->domain, architectural_iopl) )
+        v->arch.pv_vcpu.iopl = iret_saved.rflags & X86_EFLAGS_IOPL;
+
     regs->rip    = iret_saved.rip;
     regs->cs     = iret_saved.cs | 3; /* force guest privilege */
     regs->rflags = ((iret_saved.rflags & ~(X86_EFLAGS_IOPL|X86_EFLAGS_VM))

diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index f6f5a109a5fd1cc154147fe9086b5adb141b6598..c10129d70ce6d2e56347caf90b8fa43eeece5989 100644 (file)
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -331,6 +331,7 @@ extern unsigned long xen_phys_start;
                                   (1UL << VMASST_TYPE_4gb_segments_notify) | \
                                   (1UL << VMASST_TYPE_writable_pagetables) | \
                                   (1UL << VMASST_TYPE_pae_extended_cr3)    | \
+                                  (1UL << VMASST_TYPE_architectural_iopl)  | \
                                   (1UL << VMASST_TYPE_m2p_strict))
 #define VM_ASSIST_VALID          NATIVE_VM_ASSIST_VALID
 #define COMPAT_VM_ASSIST_VALID   (NATIVE_VM_ASSIST_VALID & \

diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index de60def5b7663af28f0b79d9076aedefec40fbff..5f2f27f354759a85438438d4bba42c36a961d1ab 100644 (file)
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -470,7 +470,9 @@ struct pv_vcpu
     /* I/O-port access bitmap. */
     XEN_GUEST_HANDLE(uint8) iobmp; /* Guest kernel vaddr of the bitmap. */
     unsigned int iobmp_limit; /* Number of ports represented in the bitmap. */
-    unsigned int iopl;        /* Current IOPL for this VCPU. */
+#define IOPL(val) MASK_INSR(val, X86_EFLAGS_IOPL)
+    unsigned int iopl;        /* Current IOPL for this VCPU, shifted left by
+                               * 12 to match the eflags register. */
 
     /* Current LDT details. */
     unsigned long shadow_ldt_mapcnt;

diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index 435d78902ad3cedaff4e8911b638ab185bb2d53e..97a5ae5c452b811bf627c384322b2bbdf37512c9 100644 (file)
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -502,6 +502,14 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
 /* x86/PAE guests: support PDPTs above 4GB. */
 #define VMASST_TYPE_pae_extended_cr3     3
 
+/*
+ * x86 guests: Sane behaviour for virtual iopl
+ *  - virtual iopl updated from do_iret() hypercalls.
+ *  - virtual iopl reported in bounce frames.
+ *  - guest kernels assumed to be level 0 for the purpose of iopl checks.
+ */
+#define VMASST_TYPE_architectural_iopl   4
+
 /*
  * x86/64 guests: strictly hide M2P from user mode.
  * This allows the guest to control respective hypervisor behavior: