[Xen-changelog] [xen master] x86/spec_ctrl: Updates to retpoline-safety decision making

[patchbot@xxxxxxx]

commit 1232378bd2fef45f613db049b33852fdf84d7ddf
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Apr 17 12:48:01 2018 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Apr 19 17:28:23 2018 +0100

    x86/spec_ctrl: Updates to retpoline-safety decision making
    
    All of this is as recommended by the Intel whitepaper:
    
    
https://software.intel.com/sites/default/files/managed/1d/46/Retpoline-A-Branch-Target-Injection-Mitigation.pdf
    
    The 'RSB Alternative' bit in MSR_ARCH_CAPABILITIES may be set by a 
hypervisor
    to indicate that the virtual machine may migrate to a processor which isn't
    retpoline-safe.  Introduce a shortened name (to reduce code volume), treat 
it
    as authorative in retpoline_safe(), and print its value along with the other
    ARCH_CAPS bits.
    
    The exact processor models which do have RSB semantics which fall back to 
BTB
    predictions are enumerated, and include Kabylake and Coffeelake.  Leave a
    printk() in the default case to help identify cases which aren't covered.
    
    The exact microcode versions from Broadwell RSB-safety are taken from the
    referenced microcode update file (adjusting for the known-bad microcode
    versions).  Despite the exact wording of the text, it is only Broadwell
    processors which need a microcode check.
    
    In practice, this means that all Broadwell hardware with up-to-date 
microcode
    will use retpoline in preference to IBRS, which will be a performance
    improvement for desktop and server systems which would previously always opt
    for IBRS over retpoline.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/spec_ctrl.c        | 51 +++++++++++++++++++++++++++++++++++------
 xen/include/asm-x86/msr-index.h |  1 +
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 5b5ec90fd8..bab859583f 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -113,12 +113,13 @@ static void __init print_details(enum ind_thunk thunk)
     printk(XENLOG_DEBUG "Speculative mitigation facilities:\n");
 
     /* Hardware features which pertain to speculative mitigations. */
-    printk(XENLOG_DEBUG "  Hardware features:%s%s%s%s%s\n",
+    printk(XENLOG_DEBUG "  Hardware features:%s%s%s%s%s%s\n",
            (_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ? " IBRS/IBPB" : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_STIBP)) ? " STIBP"     : "",
            (e8b  & cpufeat_mask(X86_FEATURE_IBPB))  ? " IBPB"      : "",
            (caps & ARCH_CAPABILITIES_IBRS_ALL)      ? " IBRS_ALL"  : "",
-           (caps & ARCH_CAPABILITIES_RDCL_NO)       ? " RDCL_NO"   : "");
+           (caps & ARCH_CAPABILITIES_RDCL_NO)       ? " RDCL_NO"   : "",
+           (caps & ARCH_CAPS_RSBA)                  ? " RBSA"      : "");
 
     /* Compiled-in support which pertains to BTI mitigations. */
     if ( IS_ENABLED(CONFIG_INDIRECT_THUNK) )
@@ -151,6 +152,20 @@ static bool __init retpoline_safe(void)
          boot_cpu_data.x86 != 6 )
         return false;
 
+    if ( boot_cpu_has(X86_FEATURE_ARCH_CAPS) )
+    {
+        uint64_t caps;
+
+        rdmsrl(MSR_ARCH_CAPABILITIES, caps);
+
+        /*
+         * RBSA may be set by a hypervisor to indicate that we may move to a
+         * processor which isn't retpoline-safe.
+         */
+        if ( caps & ARCH_CAPS_RSBA )
+            return false;
+    }
+
     switch ( boot_cpu_data.x86_model )
     {
     case 0x17: /* Penryn */
@@ -177,18 +192,40 @@ static bool __init retpoline_safe(void)
          * versions.
          */
     case 0x3d: /* Broadwell */
-        return ucode_rev >= 0x28;
+        return ucode_rev >= 0x2a;
     case 0x47: /* Broadwell H */
-        return ucode_rev >= 0x1b;
+        return ucode_rev >= 0x1d;
     case 0x4f: /* Broadwell EP/EX */
-        return ucode_rev >= 0xb000025;
+        return ucode_rev >= 0xb000021;
     case 0x56: /* Broadwell D */
-        return false; /* TBD. */
+        switch ( boot_cpu_data.x86_mask )
+        {
+        case 2:  return ucode_rev >= 0x15;
+        case 3:  return ucode_rev >= 0x7000012;
+        case 4:  return ucode_rev >= 0xf000011;
+        case 5:  return ucode_rev >= 0xe000009;
+        default:
+            printk("Unrecognised CPU stepping %#x - assuming not reptpoline 
safe\n",
+                   boot_cpu_data.x86_mask);
+            return false;
+        }
+        break;
 
         /*
-         * Skylake and later processors are not retpoline-safe.
+         * Skylake, Kabylake and Cannonlake processors are not retpoline-safe.
          */
+    case 0x4e:
+    case 0x55:
+    case 0x5e:
+    case 0x66:
+    case 0x67:
+    case 0x8e:
+    case 0x9e:
+        return false;
+
     default:
+        printk("Unrecognised CPU model %#x - assuming not reptpoline safe\n",
+               boot_cpu_data.x86_model);
         return false;
     }
 }
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index 8416756f02..c9f44ebdb3 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -42,6 +42,7 @@
 #define MSR_ARCH_CAPABILITIES          0x0000010a
 #define ARCH_CAPABILITIES_RDCL_NO      (_AC(1, ULL) << 0)
 #define ARCH_CAPABILITIES_IBRS_ALL     (_AC(1, ULL) << 1)
+#define ARCH_CAPS_RSBA                 (_AC(1, ULL) << 2)
 
 /* Intel MSRs. Some also available on other CPUs */
 #define MSR_IA32_PERFCTR0              0x000000c1
--
generated by git-patchbot for /home/xen/git/xen.git#master

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