Subject: x86/spec-ctrl: CPUID/MSR definitions for Special Register Buffer Data Sampling
From: Andrew Cooper <[email-masked]>

This is part of XSA-320 / CVE-2020-0543

Signed-off-by: Andrew Cooper <[email-masked]>
Reviewed-by: Jan Beulich <[email-masked]>
Acked-by: Wei Liu <[email-masked]>

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 2d4d9639d6..b7c2b99298 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -504,10 +504,10 @@ accounting for hardware capabilities as enumerated via CPUID.
 
 Currently accepted:
 
-The Speculation Control hardware features `md-clear`, `ibrsb`, `stibp`, `ibpb`,
-`l1d-flush` and `ssbd` are used by default if available and applicable.  They can
-be ignored, e.g. `no-ibrsb`, at which point Xen won't use them itself, and
-won't offer them to guests.
+The Speculation Control hardware features `srbds-ctrl`, `md-clear`, `ibrsb`,
+`stibp`, `ibpb`, `l1d-flush` and `ssbd` are used by default if available and
+applicable.  They can be ignored, e.g. `no-ibrsb`, at which point Xen won't
+use them itself, and won't offer them to guests.
 
 `rdrand` can be used to override the default disabling of the feature on certain
 AMD systems.  Its negative form can of course also be used to suppress use and
diff --git a/tools/libxl/libxl_cpuid.c b/tools/libxl/libxl_cpuid.c
index c31dd1f304..4e4852ddeb 100644
--- a/tools/libxl/libxl_cpuid.c
+++ b/tools/libxl/libxl_cpuid.c
@@ -214,6 +214,7 @@ int libxl_cpuid_parse_config(libxl_cpuid_policy_list *cpuid, const char* str)
 
         {"avx512-4vnniw",0x00000007,  0, CPUID_REG_EDX,  2,  1},
         {"avx512-4fmaps",0x00000007,  0, CPUID_REG_EDX,  3,  1},
+        {"srbds-ctrl",   0x00000007,  0, CPUID_REG_EDX,  9,  1},
         {"md-clear",     0x00000007,  0, CPUID_REG_EDX, 10,  1},
         {"serialize",    0x00000007,  0, CPUID_REG_EDX, 14,  1},
         {"cet-ibt",      0x00000007,  0, CPUID_REG_EDX, 20,  1},
diff --git a/tools/misc/xen-cpuid.c b/tools/misc/xen-cpuid.c
index 8578077545..8d8f3532a2 100644
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -160,6 +160,7 @@ static const char *const str_7d0[32] =
     [ 2] = "avx512_4vnniw", [ 3] = "avx512_4fmaps",
     [ 4] = "fsrm",
 
+    /*  8 */                [ 9] = "srbds-ctrl",
     [10] = "md-clear",
     /* 12 */                [13] = "tsx-force-abort",
     [14] = "serialize",
diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index dcacae58de..0bfb5839b2 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -167,6 +167,7 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
     case MSR_CORE_CAPABILITIES:
     case MSR_TSX_FORCE_ABORT:
     case MSR_TSX_CTRL:
+    case MSR_MCU_OPT_CTRL:
     case MSR_U_CET:
     case MSR_S_CET:
     case MSR_PL0_SSP ... MSR_INTERRUPT_SSP_TABLE:
@@ -327,6 +328,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
     case MSR_TEST_CTRL:
     case MSR_TSX_FORCE_ABORT:
     case MSR_TSX_CTRL:
+    case MSR_MCU_OPT_CTRL:
     case MSR_U_CET:
     case MSR_S_CET:
     case MSR_PL0_SSP ... MSR_INTERRUPT_SSP_TABLE:
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index a94be2d594..a5dfff80c5 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -312,12 +312,13 @@ static void __init print_details(enum ind_thunk thunk, uint64_t caps)
     printk("Speculative mitigation facilities:\n");
 
     /* Hardware features which pertain to speculative mitigations. */
-    printk("  Hardware features:%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
+    printk("  Hardware features:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s\n",
            (_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ? " IBRS/IBPB" : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_STIBP)) ? " STIBP"     : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_L1D_FLUSH)) ? " L1D_FLUSH" : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_SSBD))  ? " SSBD"      : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_MD_CLEAR)) ? " MD_CLEAR" : "",
+           (_7d0 & cpufeat_mask(X86_FEATURE_SRBDS_CTRL)) ? " SRBDS_CTRL" : "",
            (e8b  & cpufeat_mask(X86_FEATURE_IBPB))  ? " IBPB"      : "",
            (caps & ARCH_CAPS_IBRS_ALL)              ? " IBRS_ALL"  : "",
            (caps & ARCH_CAPS_RDCL_NO)               ? " RDCL_NO"   : "",
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index a4dc48f51f..b328a47ed8 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -66,6 +66,9 @@
 #define  TSX_CTRL_RTM_DISABLE               (_AC(1, ULL) <<  0)
 #define  TSX_CTRL_CPUID_CLEAR               (_AC(1, ULL) <<  1)
 
+#define MSR_MCU_OPT_CTRL                    0x00000123
+#define  MCU_OPT_CTRL_RNGDS_MITG_DIS        (_AC(1, ULL) <<  0)
+
 #define MSR_U_CET                           0x000006a0
 #define MSR_S_CET                           0x000006a2
 #define  CET_SHSTK_EN                       (_AC(1, ULL) <<  0)
diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index 8347a405ac..5ca35d9d97 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -259,6 +259,7 @@ XEN_CPUFEATURE(AMD_PPIN,      8*32+23) /*   Protected Processor Inventory Number
 /* Intel-defined CPU features, CPUID level 0x00000007:0.edx, word 9 */
 XEN_CPUFEATURE(AVX512_4VNNIW, 9*32+ 2) /*A  AVX512 Neural Network Instructions */
 XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A  AVX512 Multiply Accumulation Single Precision */
+XEN_CPUFEATURE(SRBDS_CTRL,    9*32+ 9) /*   MSR_MCU_OPT_CTRL and RNGDS_MITG_DIS. */
 XEN_CPUFEATURE(MD_CLEAR,      9*32+10) /*A  VERW clears microarchitectural buffers */
 XEN_CPUFEATURE(TSX_FORCE_ABORT, 9*32+13) /* MSR_TSX_FORCE_ABORT.RTM_ABORT */
 XEN_CPUFEATURE(SERIALIZE,     9*32+14) /*a  SERIALIZE insn */