x86/Intel: Mitigations for GPZ SP4 - Speculative Store Bypass

To combat GPZ SP4 "Speculative Store Bypass", Intel have extended their
speculative sidechannel mitigations specification as follows:

 * A feature bit to indicate that Speculative Store Bypass Disable is
   supported.
 * A new bit in MSR_SPEC_CTRL which, when set, disables memory disambiguation
   in the pipeline.
 * A new bit in MSR_ARCH_CAPABILITIES, which will be set in future hardware,
   indicating that the hardware is not susceptible to Speculative Store Bypass
   sidechannels.

For contemporary processors, this interface will be implemented via a
microcode update.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 9df52a25e0e95a0b9971aa2fc26c5c6a5cbdf4ef
master date: 2018-05-21 14:20:06 +0100

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index e2f4ae35d5e45706a1929f2f506db47db833c2b8..3d54bafd3d30f012d694743c79e7587796d01ab9 100644 (file)
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -440,9 +440,10 @@ accounting for hardware capabilities as enumerated via CPUID.
 
 Currently accepted:
 
-The Speculation Control hardware features `ibrsb`, `stibp`, `ibpb` are used by
-default if avaiable.  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 `ibrsb`, `stibp`, `ibpb`, `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.
 
 ### cpuid\_mask\_cpu (AMD only)
 > `= fam_0f_rev_c | fam_0f_rev_d | fam_0f_rev_e | fam_0f_rev_f | fam_0f_rev_g | fam_10_rev_b | fam_10_rev_c | fam_11_rev_b`
@@ -1424,7 +1425,7 @@ protect itself, and Xen's ability to virtualise support for guests to use.
   respectively.
 * `msr-sc=` offers control over Xen's support for manipulating MSR\_SPEC\_CTRL
   on entry and exit.  These blocks are necessary to virtualise support for
-  guests and if disabled, guests will be unable to use IBRS/STIBP/etc.
+  guests and if disabled, guests will be unable to use IBRS/STIBP/SSBD/etc.
 * `rsb=` offers control over whether to overwrite the Return Stack Buffer /
   Return Address Stack on entry to Xen.
 
@@ -1446,7 +1447,8 @@ prediction barriers on vcpu context switches.
 On hardware supporting SSBD (Speculative Store Bypass Disable), the `ssbd=`
 option can be used to force or prevent Xen using the feature itself.  On AMD
 hardware, this is a global option applied at boot, and not virtualised for
-guest use.
+guest use.  On Intel hardware, the feature is virtualised for guests,
+independently of Xen's choice of setting.
 
 ### sync\_console
 > `= <boolean>`

diff --git a/tools/libxl/libxl_cpuid.c b/tools/libxl/libxl_cpuid.c
index 17e9f0f54980251bc68f2d951d87a56456caf70b..6a28fec97f191acc9aa509d3fc379b10d02247a9 100644 (file)
--- a/tools/libxl/libxl_cpuid.c
+++ b/tools/libxl/libxl_cpuid.c
@@ -160,6 +160,7 @@ int libxl_cpuid_parse_config(libxl_cpuid_policy_list *cpuid, const char* str)
         {"fpu",          0x00000001, NA, CPUID_REG_EDX,  0,  1},
         {"ibrsb",        0x00000007,  0, CPUID_REG_EDX, 26,  1},
         {"stibp",        0x00000007,  0, CPUID_REG_EDX, 27,  1},
+        {"ssbd",         0x00000007,  0, CPUID_REG_EDX, 31,  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},

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 67f75b9ff0bf3c417673af281c1f70e88e02feff..11839f3e80dcb5df436b8bbb95e86b1377b30149 100644 (file)
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4625,7 +4625,8 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, unsigned int *ebx,
         if ( count == 0 )
         {
             if ( !boot_cpu_has(X86_FEATURE_SC_MSR_HVM) )
-                *edx &= ~cpufeat_mask(X86_FEATURE_IBRSB);
+                *edx &= ~(cpufeat_mask(X86_FEATURE_IBRSB) |
+                          cpufeat_mask(X86_FEATURE_SSBD));
 
             /*
              * Override STIBP to match IBRS.  Guests can safely use STIBP

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index c3adee57cd0bcf66c45dbedb8e70bf5be22eff60..f3831e0575a94b10c528c72c808b04254c3a48f1 100644 (file)
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -135,6 +135,11 @@ static int __init parse_xen_cpuid(const char *s)
             if ( !val )
                 setup_clear_cpu_cap(X86_FEATURE_STIBP);
         }
+        else if ( (val = parse_boolean("ssbd", s, ss)) >= 0 )
+        {
+            if ( !val )
+                setup_clear_cpu_cap(X86_FEATURE_SSBD);
+        }
         else
             rc = -EINVAL;
 

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index ae9f830b5114f1ebcca96bb737d2323806bff5a5..c88e7597246620e9078b36281f0b6a8ecb5d9cf4 100644 (file)
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -192,13 +192,15 @@ 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\n",
+    printk("  Hardware features:%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_SSBD))  ? " SSBD"      : "",
            (e8b  & cpufeat_mask(X86_FEATURE_IBPB))  ? " IBPB"      : "",
            (caps & ARCH_CAPABILITIES_IBRS_ALL)      ? " IBRS_ALL"  : "",
            (caps & ARCH_CAPABILITIES_RDCL_NO)       ? " RDCL_NO"   : "",
-           (caps & ARCH_CAPS_RSBA)                  ? " RSBA"      : "");
+           (caps & ARCH_CAPS_RSBA)                  ? " RSBA"      : "",
+           (caps & ARCH_CAPS_SSB_NO)                ? " SSB_NO"    : "");
 
     /* Compiled-in support which pertains to BTI mitigations. */
 #ifdef CONFIG_INDIRECT_THUNK
@@ -206,13 +208,16 @@ static void __init print_details(enum ind_thunk thunk, uint64_t caps)
 #endif
 
     /* Settings for Xen's protection, irrespective of guests. */
-    printk("  Xen settings: BTI-Thunk %s, SPEC_CTRL: %s, Other:%s\n",
+    printk("  Xen settings: BTI-Thunk %s, SPEC_CTRL: %s%s, Other:%s\n",
            thunk == THUNK_NONE      ? "N/A" :
            thunk == THUNK_RETPOLINE ? "RETPOLINE" :
            thunk == THUNK_LFENCE    ? "LFENCE" :
            thunk == THUNK_JMP       ? "JMP" : "?",
            !use_spec_ctrl                            ?  "No" :
            (default_xen_spec_ctrl & SPEC_CTRL_IBRS)  ?  "IBRS+" :  "IBRS-",
+           !use_spec_ctrl || !boot_cpu_has(X86_FEATURE_SSBD)
+                                                     ? "" :
+           (default_xen_spec_ctrl & SPEC_CTRL_SSBD)  ? " SSBD+" : " SSBD-",
            opt_ibpb                                  ? " IBPB"  : "");
 
     /*
@@ -411,6 +416,10 @@ void __init init_speculation_mitigations(void)
         }
     }
 
+    /* If we have SSBD available, see whether we should use it. */
+    if ( boot_cpu_has(X86_FEATURE_SSBD) && use_spec_ctrl && opt_ssbd )
+        default_xen_spec_ctrl |= SPEC_CTRL_SSBD;
+
     /*
      * PV guests can poison the RSB to any virtual address from which
      * they can execute a call instruction.  This is necessarily outside

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 1e71c05b28df7241082474e76bdfbb6d9ee7d92a..b759f9ef3b6c1405a3a8ec41d59837c4c8395359 100644 (file)
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -880,7 +880,8 @@ void pv_cpuid(struct cpu_user_regs *regs)
             if ( regs->_ecx == 0 )
             {
                 if ( !boot_cpu_has(X86_FEATURE_SC_MSR_PV) )
-                    d &= ~cpufeat_mask(X86_FEATURE_IBRSB);
+                    d &= ~(cpufeat_mask(X86_FEATURE_IBRSB) |
+                           cpufeat_mask(X86_FEATURE_SSBD));
 
                 /*
                  * Override STIBP to match IBRS.  Guests can safely use STIBP
@@ -970,7 +971,8 @@ void pv_cpuid(struct cpu_user_regs *regs)
                   cpufeat_mask(X86_FEATURE_FSGSBASE));
 
             if ( boot_cpu_has(X86_FEATURE_SC_MSR_PV) )
-                d &= cpufeat_mask(X86_FEATURE_IBRSB);
+                d &= cpufeat_mask(X86_FEATURE_IBRSB) |
+                     cpufeat_mask(X86_FEATURE_SSBD);
             else
                 d = 0;
 

diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index 22429db282d4c5ec86616341817be2ca6314617a..20c6d627dda184e17668099441db4cfa60e192f0 100644 (file)
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -171,6 +171,7 @@
 #define X86_FEATURE_IBRSB      (9*32+26) /* IBRS and IBPB support (used by Intel) */
 #define X86_FEATURE_STIBP      (9*32+27) /* STIBP */
 #define X86_FEATURE_ARCH_CAPS  (9*32+29) /* IA32_ARCH_CAPABILITIES MSR */
+#define X86_FEATURE_SSBD       (9*32+31) /* MSR_SPEC_CTRL.SSBD available */
 
 /* An alias of a feature we know is always going to be present. */
 #define X86_FEATURE_ALWAYS      X86_FEATURE_LM

diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index e5845a7871224b5aede7358d646d4480b61fc170..c21801c1d15cec64a1ba99b7a2ed6ef320a84f10 100644 (file)
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -35,6 +35,7 @@
 #define MSR_SPEC_CTRL                  0x00000048
 #define SPEC_CTRL_IBRS                 (_AC(1, ULL) << 0)
 #define SPEC_CTRL_STIBP                        (_AC(1, ULL) << 1)
+#define SPEC_CTRL_SSBD                 (_AC(1, ULL) << 2)
 
 #define MSR_PRED_CMD                   0x00000049
 #define PRED_CMD_IBPB                  (_AC(1, ULL) << 0)
@@ -43,6 +44,7 @@
 #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)
+#define ARCH_CAPS_SSB_NO               (_AC(1, ULL) << 4)
 
 /* Intel MSRs. Some also available on other CPUs */
 #define MSR_IA32_PERFCTR0              0x000000c1