x86/speculation: Add support for STIBP always-on preferred mode

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
CVE-2017-5715

(cherry picked from commit 20c3a2c33e9fdc82e9e8e8d2a6445b3256d20191)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index fcd336b0d882352d92551d6a48b9df9ea1faeb41..62411fd1cef787788cfe29ae8d104c7b8bcf7de2 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -284,6 +284,7 @@
 #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. */

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index a633767419f297974068e7c119f4960abbc542a0..13a29b270cc075f23dc8100a65e249d76405a45f 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -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,
 };

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 93077e2fa009a2f93de5ca352750b691d52bf2c5..35743822102fc8d78b5d5b071e3c6263b433ea80 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -261,10 +261,11 @@ 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 {
@@ -354,6 +355,15 @@ 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);
@@ -607,6 +617,7 @@ 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:
@@ -809,7 +820,8 @@ 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);
@@ -822,7 +834,8 @@ 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)
@@ -893,6 +906,7 @@ 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;
@@ -1082,6 +1096,8 @@ 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))