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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Xen-devel <xen-devel@lists.xen.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Jan Beulich <JBeulich@suse.com>,
	Andy Lutomirski <luto@amacapital.net>
Subject: [PATCH 2/2] xen/x86: Introduce a new VMASSIST for architectural behaviour of iopl
Date: Wed, 16 Mar 2016 20:05:49 +0000	[thread overview]
Message-ID: <1458158749-21846-3-git-send-email-andrew.cooper3@citrix.com> (raw)
In-Reply-To: <1458158749-21846-1-git-send-email-andrew.cooper3@citrix.com>

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.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/arch/x86/domain.c              | 10 +++++++---
 xen/arch/x86/physdev.c             |  2 +-
 xen/arch/x86/traps.c               |  8 ++++++--
 xen/arch/x86/x86_64/asm-offsets.c  |  3 +++
 xen/arch/x86/x86_64/compat/entry.S |  7 ++++++-
 xen/arch/x86/x86_64/compat/traps.c |  4 ++++
 xen/arch/x86/x86_64/entry.S        |  7 ++++++-
 xen/arch/x86/x86_64/traps.c        |  3 +++
 xen/include/asm-x86/config.h       |  1 +
 xen/include/asm-x86/domain.h       |  3 ++-
 xen/include/public/xen.h           |  8 ++++++++
 11 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index a6d721b..36b9aaa 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1001,7 +1001,7 @@ 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. */
@@ -1742,8 +1742,10 @@ 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) )
             {
@@ -1788,8 +1790,10 @@ 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) |
diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
index 1cb9b58..5a49796 100644
--- 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 564a107..9754a2f 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1806,7 +1806,9 @@ static int guest_io_okay(
 #define TOGGLE_MODE() if ( user_mode ) toggle_guest_mode(v)
 
     if ( !vm86_mode(regs) &&
-         (v->arch.pv_vcpu.iopl >= (guest_kernel_mode(v, regs) ? 1 : 3)) )
+         (MASK_EXTR(v->arch.pv_vcpu.iopl, X86_EFLAGS_IOPL) >=
+          (guest_kernel_mode(v, regs) ?
+           (VM_ASSIST(v->domain, architectural_iopl) ? 0 : 1) : 3)) )
         return 1;
 
     if ( v->arch.pv_vcpu.iobmp_limit > (port + bytes) )
@@ -2367,7 +2369,9 @@ 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 ( MASK_EXTR(v->arch.pv_vcpu.iopl, X86_EFLAGS_IOPL) <
+             (guest_kernel_mode(v, regs) ?
+              (VM_ASSIST(v->domain, architectural_iopl) ? 0 : 1) : 3) )
             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 447c650..fa37ee0 100644
--- 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 36a8eae..45efd33 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -277,9 +277,14 @@ 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
+        movq  VCPU_domain(%rbx),%rcx    # if ( VM_ASSIST(v->domain, architectural_iopl) )
+        testb $1 << VMASST_TYPE_architectural_iopl,DOMAIN_vm_assist(%rcx)
+        jz    .Lft6
+        movzwl 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 bbf18e4..a6afb26 100644
--- 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 221de01..1d6dedc 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -362,9 +362,14 @@ __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
+        movq  VCPU_domain(%rbx),%rcx    # if ( VM_ASSIST(v->domain, architectural_iopl) )
+        testb $1 << VMASST_TYPE_architectural_iopl,DOMAIN_vm_assist(%rcx)
+        jz    .Lft5
+        movzwl 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 26e2dd7..19f58a1 100644
--- 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 4527ce3..4fe8a94 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -332,6 +332,7 @@ 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 de60def..a6cbae0 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -470,7 +470,8 @@ 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. */
+    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 64ba7ab..4f73ded 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -502,6 +502,14 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
 #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:
  * - when not set, L4 tables get created with the respective slot blank,
-- 
2.1.4


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  parent reply	other threads:[~2016-03-16 20:05 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-16 20:05 [PATCH 0/2] XSA-171 Followup work Andrew Cooper
2016-03-16 20:05 ` [PATCH 1/2] xen/x86: Don't hold TRAPBOUNCE_flags in %cl during create_bounce_frame Andrew Cooper
2016-03-16 20:05 ` Andrew Cooper [this message]
2016-03-17 10:25   ` [PATCH 2/2] xen/x86: Introduce a new VMASSIST for architectural behaviour of iopl Jan Beulich
2016-03-17 10:45     ` Andrew Cooper
2016-03-17 11:00       ` Jan Beulich
2016-03-17 11:05         ` Andrew Cooper

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