x86/speculation: Add support for STIBP always-on preferred mode
authorThomas Lendacky <Thomas.Lendacky@amd.com>
Thu, 13 Dec 2018 23:03:54 +0000 (23:03 +0000)
committerThomas Gleixner <tglx@linutronix.de>
Tue, 18 Dec 2018 13:13:33 +0000 (14:13 +0100)
Different AMD processors may have different implementations of STIBP.
When STIBP is conditionally enabled, some implementations would benefit
from having STIBP always on instead of toggling the STIBP bit through MSR
writes. This preference is advertised through a CPUID feature bit.

When conditional STIBP support is requested at boot and the CPU advertises
STIBP always-on mode as preferred, switch to STIBP "on" support. To show
that this transition has occurred, create a new spectre_v2_user_mitigation
value and a new spectre_v2_user_strings message. The new mitigation value
is used in spectre_v2_user_select_mitigation() to print the new mitigation
message as well as to return a new string from stibp_state().

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/20181213230352.6937.74943.stgit@tlendack-t1.amdoffice.net
arch/x86/include/asm/cpufeatures.h
arch/x86/include/asm/nospec-branch.h
arch/x86/kernel/cpu/bugs.c

index 28c4a502b4197cce9ae968deb8ea2fe7797e8da4..df8e94e2f7beada251e513104195698dd9c735a7 100644 (file)
 #define X86_FEATURE_AMD_IBPB           (13*32+12) /* "" Indirect Branch Prediction Barrier */
 #define X86_FEATURE_AMD_IBRS           (13*32+14) /* "" Indirect Branch Restricted Speculation */
 #define X86_FEATURE_AMD_STIBP          (13*32+15) /* "" Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_AMD_STIBP_ALWAYS_ON        (13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
 #define X86_FEATURE_AMD_SSBD           (13*32+24) /* "" Speculative Store Bypass Disable */
 #define X86_FEATURE_VIRT_SSBD          (13*32+25) /* Virtualized Speculative Store Bypass Disable */
 #define X86_FEATURE_AMD_SSB_NO         (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
index 032b6009baab4a96d04d57112f2f48e1182fb8c2..dad12b767ba069ede01be842e25a5d04afa35297 100644 (file)
@@ -232,6 +232,7 @@ enum spectre_v2_mitigation {
 enum spectre_v2_user_mitigation {
        SPECTRE_V2_USER_NONE,
        SPECTRE_V2_USER_STRICT,
+       SPECTRE_V2_USER_STRICT_PREFERRED,
        SPECTRE_V2_USER_PRCTL,
        SPECTRE_V2_USER_SECCOMP,
 };
index 58689ac64440d0657f87d76b93244b63e88cb723..77bf22546ddd4945b5a8d0db8dcf71551d4e610c 100644 (file)
@@ -262,10 +262,11 @@ enum spectre_v2_user_cmd {
 };
 
 static const char * const spectre_v2_user_strings[] = {
-       [SPECTRE_V2_USER_NONE]          = "User space: Vulnerable",
-       [SPECTRE_V2_USER_STRICT]        = "User space: Mitigation: STIBP protection",
-       [SPECTRE_V2_USER_PRCTL]         = "User space: Mitigation: STIBP via prctl",
-       [SPECTRE_V2_USER_SECCOMP]       = "User space: Mitigation: STIBP via seccomp and prctl",
+       [SPECTRE_V2_USER_NONE]                  = "User space: Vulnerable",
+       [SPECTRE_V2_USER_STRICT]                = "User space: Mitigation: STIBP protection",
+       [SPECTRE_V2_USER_STRICT_PREFERRED]      = "User space: Mitigation: STIBP always-on protection",
+       [SPECTRE_V2_USER_PRCTL]                 = "User space: Mitigation: STIBP via prctl",
+       [SPECTRE_V2_USER_SECCOMP]               = "User space: Mitigation: STIBP via seccomp and prctl",
 };
 
 static const struct {
@@ -355,6 +356,15 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
                break;
        }
 
+       /*
+        * At this point, an STIBP mode other than "off" has been set.
+        * If STIBP support is not being forced, check if STIBP always-on
+        * is preferred.
+        */
+       if (mode != SPECTRE_V2_USER_STRICT &&
+           boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
+               mode = SPECTRE_V2_USER_STRICT_PREFERRED;
+
        /* Initialize Indirect Branch Prediction Barrier */
        if (boot_cpu_has(X86_FEATURE_IBPB)) {
                setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
@@ -610,6 +620,7 @@ void arch_smt_update(void)
        case SPECTRE_V2_USER_NONE:
                break;
        case SPECTRE_V2_USER_STRICT:
+       case SPECTRE_V2_USER_STRICT_PREFERRED:
                update_stibp_strict();
                break;
        case SPECTRE_V2_USER_PRCTL:
@@ -812,7 +823,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
                 * Indirect branch speculation is always disabled in strict
                 * mode.
                 */
-               if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+               if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+                   spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
                        return -EPERM;
                task_clear_spec_ib_disable(task);
                task_update_spec_tif(task);
@@ -825,7 +837,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
                 */
                if (spectre_v2_user == SPECTRE_V2_USER_NONE)
                        return -EPERM;
-               if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+               if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+                   spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
                        return 0;
                task_set_spec_ib_disable(task);
                if (ctrl == PR_SPEC_FORCE_DISABLE)
@@ -896,6 +909,7 @@ static int ib_prctl_get(struct task_struct *task)
                        return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
                return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
        case SPECTRE_V2_USER_STRICT:
+       case SPECTRE_V2_USER_STRICT_PREFERRED:
                return PR_SPEC_DISABLE;
        default:
                return PR_SPEC_NOT_AFFECTED;
@@ -1089,6 +1103,8 @@ static char *stibp_state(void)
                return ", STIBP: disabled";
        case SPECTRE_V2_USER_STRICT:
                return ", STIBP: forced";
+       case SPECTRE_V2_USER_STRICT_PREFERRED:
+               return ", STIBP: always-on";
        case SPECTRE_V2_USER_PRCTL:
        case SPECTRE_V2_USER_SECCOMP:
                if (static_key_enabled(&switch_to_cond_stibp))