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[Xen-changelog] [xen staging-4.9] x86/pv: Introduce and use x86emul_write_dr()



commit d674b6ea010abd809c1c5efcd828235a89416890
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri May 18 11:54:43 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 18 11:54:43 2018 +0200

    x86/pv: Introduce and use x86emul_write_dr()
    
    set_debugreg() has several bugs:
    
     * %dr4/5 should function correctly as aliases of %dr6/7 when CR4.DE is 
clear.
     * Attempting to set the upper 32 bits of %dr6/7 should fail with #GP[0]
       rather than be silently corrected and complete.
     * For emulation, the #UD and #GP[0] cases need properly distinguishing.  
Use
       -ENODEV for #UD cases, leaving -EINVAL (bad bits) and -EPERM (not 
allowed to
       use that valid bit) as before for hypercall callers.
     * A write which clears %dr7.L/G leaves the IO shadow intact, meaning that
       subsequent reads of %dr7 will see stale IO watchpoint configuration.
    
    Implement x86emul_write_dr() as a thin wrapper around set_debugreg().
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: f539ae27061c6811fd5e80e0755bf0514e22b977
    master date: 2018-04-17 15:12:36 +0100
---
 xen/arch/x86/traps.c                   | 41 ++++++++++++++++++++++++++--------
 xen/arch/x86/x86_emulate.c             | 24 ++++++++++++++++++++
 xen/arch/x86/x86_emulate/x86_emulate.h |  2 ++
 3 files changed, 58 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 1f3881e5b3..6b7d075d9f 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -2494,13 +2494,6 @@ static int priv_op_write_cr(unsigned int reg, unsigned 
long val,
     return X86EMUL_UNHANDLEABLE;
 }
 
-static int priv_op_write_dr(unsigned int reg, unsigned long val,
-                            struct x86_emulate_ctxt *ctxt)
-{
-    return do_set_debugreg(reg, val) == 0
-           ? X86EMUL_OKAY : X86EMUL_UNHANDLEABLE;
-}
-
 static inline uint64_t guest_misc_enable(uint64_t val)
 {
     val &= ~(MSR_IA32_MISC_ENABLE_PERF_AVAIL |
@@ -3011,7 +3004,7 @@ static const struct x86_emulate_ops priv_op_ops = {
     .read_cr             = priv_op_read_cr,
     .write_cr            = priv_op_write_cr,
     .read_dr             = x86emul_read_dr,
-    .write_dr            = priv_op_write_dr,
+    .write_dr            = x86emul_write_dr,
     .read_msr            = priv_op_read_msr,
     .write_msr           = priv_op_write_msr,
     .cpuid               = pv_emul_cpuid,
@@ -4187,6 +4180,12 @@ void activate_debugregs(const struct vcpu *curr)
     }
 }
 
+/*
+ * Used by hypercalls and the emulator.
+ *  -ENODEV => #UD
+ *  -EINVAL => #GP Invalid bit
+ *  -EPERM  => #GP Valid bit, but not permitted to use
+ */
 long set_debugreg(struct vcpu *v, unsigned int reg, unsigned long value)
 {
     int i;
@@ -4218,7 +4217,17 @@ long set_debugreg(struct vcpu *v, unsigned int reg, 
unsigned long value)
         if ( v == curr ) 
             write_debugreg(3, value);
         break;
+
+    case 4:
+        if ( v->arch.pv_vcpu.ctrlreg[4] & X86_CR4_DE )
+            return -ENODEV;
+
+        /* Fallthrough */
     case 6:
+        /* The upper 32 bits are strictly reserved. */
+        if ( value != (uint32_t)value )
+            return -EINVAL;
+
         /*
          * DR6: Bits 4-11,16-31 reserved (set to 1).
          *      Bit 12 reserved (set to 0).
@@ -4228,7 +4237,17 @@ long set_debugreg(struct vcpu *v, unsigned int reg, 
unsigned long value)
         if ( v == curr ) 
             write_debugreg(6, value);
         break;
+
+    case 5:
+        if ( v->arch.pv_vcpu.ctrlreg[4] & X86_CR4_DE )
+            return -ENODEV;
+
+        /* Fallthrough */
     case 7:
+        /* The upper 32 bits are strictly reserved. */
+        if ( value != (uint32_t)value )
+            return -EINVAL;
+
         /*
          * DR7: Bit 10 reserved (set to 1).
          *      Bits 11-12,14-15 reserved (set to 0).
@@ -4241,6 +4260,10 @@ long set_debugreg(struct vcpu *v, unsigned int reg, 
unsigned long value)
          */
         if ( value & DR_GENERAL_DETECT )
             return -EPERM;
+
+        /* Zero the IO shadow before recalculating the real %dr7 */
+        v->arch.debugreg[5] = 0;
+
         /* DR7.{G,L}E = 0 => debugging disabled for this domain. */
         if ( value & DR7_ACTIVE_MASK )
         {
@@ -4273,7 +4296,7 @@ long set_debugreg(struct vcpu *v, unsigned int reg, 
unsigned long value)
             write_debugreg(7, value);
         break;
     default:
-        return -EINVAL;
+        return -ENODEV;
     }
 
     v->arch.debugreg[reg] = value;
diff --git a/xen/arch/x86/x86_emulate.c b/xen/arch/x86/x86_emulate.c
index d3155a09d5..9125c67c9e 100644
--- a/xen/arch/x86/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate.c
@@ -14,6 +14,7 @@
 #include <asm/processor.h> /* current_cpu_info */
 #include <asm/xstate.h>
 #include <asm/amd.h> /* cpu_has_amd_erratum() */
+#include <asm/debugreg.h>
 
 /* Avoid namespace pollution. */
 #undef cmpxchg
@@ -81,6 +82,29 @@ int x86emul_read_dr(unsigned int reg, unsigned long *val,
     return X86EMUL_OKAY;
 }
 
+int x86emul_write_dr(unsigned int reg, unsigned long val,
+                     struct x86_emulate_ctxt *ctxt)
+{
+    struct vcpu *curr = current;
+
+    /* HVM support requires a bit more plumbing before it will work. */
+    ASSERT(is_pv_vcpu(curr));
+
+    switch ( set_debugreg(curr, reg, val) )
+    {
+    case 0:
+        return X86EMUL_OKAY;
+
+    case -ENODEV:
+        x86_emul_hw_exception(TRAP_invalid_op, X86_EVENT_NO_EC, ctxt);
+        return X86EMUL_EXCEPTION;
+
+    default:
+        x86_emul_hw_exception(TRAP_gp_fault, 0, ctxt);
+        return X86EMUL_EXCEPTION;
+    }
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h 
b/xen/arch/x86/x86_emulate/x86_emulate.h
index 1c9331c897..d1f9b85f3b 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -654,6 +654,8 @@ void x86_emulate_free_state(struct x86_emulate_state 
*state);
 
 int x86emul_read_dr(unsigned int reg, unsigned long *val,
                     struct x86_emulate_ctxt *ctxt);
+int x86emul_write_dr(unsigned int reg, unsigned long val,
+                     struct x86_emulate_ctxt *ctxt);
 
 #endif
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.9

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