# Commit 0d703a701cc4bc47773986b2796eebd28b1439b5
# Date 2018-01-16 17:45:50 +0000
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/feature: Definitions for Indirect Branch Controls

Contemporary processors are gaining Indirect Branch Controls via microcode
updates.  Intel are introducing one bit to indicate IBRS and IBPB support, and
a second bit for STIBP.  AMD are introducing IBPB only, so enumerate it with a
separate bit.

Furthermore, depending on compiler and microcode availability, we may want to
run Xen with IBRS set, or clear.

To use these facilities, we synthesise separate IBRS and IBPB bits for
internal use.  A lot of infrastructure is required before these features are
safe to offer to guests.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -540,13 +540,15 @@ static void xc_cpuid_hvm_policy(xc_inter
         {
             regs[1] = info->featureset[featureword_of(X86_FEATURE_FSGSBASE)];
             regs[2] = info->featureset[featureword_of(X86_FEATURE_PREFETCHWT1)];
+            regs[3] = info->featureset[featureword_of(X86_FEATURE_IBRSB)];
         }
         else
         {
             regs[1] = 0;
             regs[2] = 0;
+            regs[3] = 0;
         }
-        regs[0] = regs[3] = 0;
+        regs[0] = 0;
         break;
 
     case 0x0000000d:
@@ -625,13 +627,15 @@ static void xc_cpuid_pv_policy(xc_interf
         {
             regs[1] = info->featureset[featureword_of(X86_FEATURE_FSGSBASE)];
             regs[2] = info->featureset[featureword_of(X86_FEATURE_PREFETCHWT1)];
+            regs[3] = info->featureset[featureword_of(X86_FEATURE_IBRSB)];
         }
         else
         {
             regs[1] = 0;
             regs[2] = 0;
+            regs[3] = 0;
         }
-        regs[0] = regs[3] = 0;
+        regs[0] = 0;
         break;
 
     case 0x0000000d:
--- a/tools/libxl/libxl_cpuid.c
+++ b/tools/libxl/libxl_cpuid.c
@@ -158,6 +158,8 @@ int libxl_cpuid_parse_config(libxl_cpuid
         {"de",           0x00000001, NA, CPUID_REG_EDX,  2,  1},
         {"vme",          0x00000001, NA, CPUID_REG_EDX,  1,  1},
         {"fpu",          0x00000001, NA, CPUID_REG_EDX,  0,  1},
+        {"ibrsb",        0x00000007,  0, CPUID_REG_EDX, 26,  1},
+        {"stibp",        0x00000007,  0, CPUID_REG_EDX, 27,  1},
         {"topoext",      0x80000001, NA, CPUID_REG_ECX, 22,  1},
         {"tbm",          0x80000001, NA, CPUID_REG_ECX, 21,  1},
         {"nodeid",       0x80000001, NA, CPUID_REG_ECX, 19,  1},
@@ -187,6 +189,7 @@ int libxl_cpuid_parse_config(libxl_cpuid
         {"nx",           0x80000001, NA, CPUID_REG_EDX, 20,  1},
         {"syscall",      0x80000001, NA, CPUID_REG_EDX, 11,  1},
         {"procpkg",      0x00000004,  0, CPUID_REG_EAX, 26,  6},
+        {"ibpb",         0x80000008, NA, CPUID_REG_EBX, 12,  1},
         {"apicidsize",   0x80000008, NA, CPUID_REG_ECX, 12,  4},
         {"nc",           0x80000008, NA, CPUID_REG_ECX,  0,  8},
         {"svm_npt",      0x8000000a, NA, CPUID_REG_EDX,  0,  1},
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -140,7 +140,20 @@ static const char *str_e8b[32] =
 {
     [ 0] = "clzero",
 
-    [1 ... 31] = "REZ",
+    [1 ... 11] = "REZ",
+
+    [12] = "ibpb",
+
+    [13 ... 31] = "REZ",
+};
+
+static const char *str_7d0[32] =
+{
+    [0 ... 25] = "REZ",
+
+    [26] = "ibrsb",         [27] = "stibp",
+
+    [28 ... 31] = "REZ",
 };
 
 static struct {
@@ -158,6 +171,7 @@ static struct {
     { "0x00000007:0.ecx", "7c0", str_7c0 },
     { "0x80000007.edx",   "e7d", str_e7d },
     { "0x80000008.ebx",   "e8b", str_e8b },
+    { "0x00000007:0.edx", "7d0", str_7d0 },
 };
 
 #define COL_ALIGN "18"
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -321,7 +321,7 @@ static void generic_identify(struct cpui
 		cpuid_count(0x00000007, 0, &tmp,
 			    &c->x86_capability[cpufeat_word(X86_FEATURE_FSGSBASE)],
 			    &c->x86_capability[cpufeat_word(X86_FEATURE_PKU)],
-			    &tmp);
+			    &c->x86_capability[cpufeat_word(X86_FEATURE_IBRSB)]);
 }
 
 /*
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -67,8 +67,25 @@ custom_param("bti", parse_bti);
 
 static void __init print_details(enum ind_thunk thunk)
 {
+    unsigned int _7d0 = 0, e8b = 0, tmp;
+
+    /* Collect diagnostics about available mitigations. */
+    if ( boot_cpu_data.cpuid_level >= 7 )
+        cpuid_count(7, 0, &tmp, &tmp, &tmp, &_7d0);
+    if ( boot_cpu_data.extended_cpuid_level >= 0x80000008 )
+        cpuid(0x80000008, &tmp, &e8b, &tmp, &tmp);
+
     printk(XENLOG_DEBUG "Speculative mitigation facilities:\n");
 
+    /* Hardware features which pertain to speculative mitigations. */
+    if ( (_7d0 & (cpufeat_mask(X86_FEATURE_IBRSB) |
+                  cpufeat_mask(X86_FEATURE_STIBP))) ||
+         (e8b & cpufeat_mask(X86_FEATURE_IBPB)) )
+        printk(XENLOG_DEBUG "  Hardware features:%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"      : "");
+
     /* Compiled-in support which pertains to BTI mitigations. */
     if ( IS_ENABLED(CONFIG_INDIRECT_THUNK) )
         printk(XENLOG_DEBUG "  Compiled-in support: INDIRECT_THUNK\n");
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -21,6 +21,9 @@ XEN_CPUFEATURE(MFENCE_RDTSC,    (FSCAPIN
 XEN_CPUFEATURE(LFENCE_DISPATCH, (FSCAPINTS+0)*32+ 11) /* lfence set as Dispatch Serialising */
 XEN_CPUFEATURE(IND_THUNK_LFENCE,(FSCAPINTS+0)*32+ 12) /* Use IND_THUNK_LFENCE */
 XEN_CPUFEATURE(IND_THUNK_JMP,   (FSCAPINTS+0)*32+ 13) /* Use IND_THUNK_JMP */
+XEN_CPUFEATURE(XEN_IBPB,        (FSCAPINTS+0)*32+ 14) /* IBRSB || IBPB */
+XEN_CPUFEATURE(XEN_IBRS_SET,    (FSCAPINTS+0)*32+ 15) /* IBRSB && IRBS set in Xen */
+XEN_CPUFEATURE(XEN_IBRS_CLEAR,  (FSCAPINTS+0)*32+ 16) /* IBRSB && IBRS clear in Xen */
 
 #define NCAPINTS (FSCAPINTS + 1) /* N 32-bit words worth of info */
 
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -31,6 +31,14 @@
 #define EFER_LMSLE		(1<<_EFER_LMSLE)
 #define EFER_FFXSE		(1<<_EFER_FFXSE)
 
+/* Speculation Controls. */
+#define MSR_SPEC_CTRL			0x00000048
+#define SPEC_CTRL_IBRS			(_AC(1, ULL) << 0)
+#define SPEC_CTRL_STIBP			(_AC(1, ULL) << 1)
+
+#define MSR_PRED_CMD			0x00000049
+#define PRED_CMD_IBPB			(_AC(1, ULL) << 0)
+
 /* Intel MSRs. Some also available on other CPUs */
 #define MSR_IA32_PERFCTR0		0x000000c1
 #define MSR_IA32_A_PERFCTR0		0x000004c1
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -224,6 +224,11 @@ XEN_CPUFEATURE(EFRO,          7*32+10) /
 
 /* AMD-defined CPU features, CPUID level 0x80000008.ebx, word 8 */
 XEN_CPUFEATURE(CLZERO,        8*32+ 0) /*A  CLZERO instruction */
+XEN_CPUFEATURE(IBPB,          8*32+12) /*   IBPB support only (no IBRS, used by AMD) */
+
+/* Intel-defined CPU features, CPUID level 0x00000007:0.edx, word 9 */
+XEN_CPUFEATURE(IBRSB,         9*32+26) /*   IBRS and IBPB support (used by Intel) */
+XEN_CPUFEATURE(STIBP,         9*32+27) /*   STIBP */
 
 #endif /* XEN_CPUFEATURE */
 
--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -244,6 +244,11 @@ def crunch_numbers(state):
         # AMD K6-2+ and K6-III processors shipped with 3DNow+, beyond the
         # standard 3DNow in the earlier K6 processors.
         _3DNOW: [_3DNOWEXT],
+
+        # Single Thread Indirect Branch Predictors enumerates a new bit in the
+        # MSR enumerated by Indirect Branch Restricted Speculation/Indirect
+        # Branch Prediction Barrier enumeration.
+        IBRSB: [STIBP],
     }
 
     deep_features = tuple(sorted(deps.keys()))
