x86/speculation: Make "seccomp" the default mode for Speculative Store Bypass

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / cpu / bugs.c

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 94b5460cded3ea0f679542862e9ee4ca1aefdcbb..07bd00b1a8f393eca59aea7fee42a4c98a346fd4 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -375,22 +375,25 @@ enum ssb_mitigation_cmd {
        SPEC_STORE_BYPASS_CMD_AUTO,
        SPEC_STORE_BYPASS_CMD_ON,
        SPEC_STORE_BYPASS_CMD_PRCTL,
+       SPEC_STORE_BYPASS_CMD_SECCOMP,
 };
 
 static const char *ssb_strings[] = {
        [SPEC_STORE_BYPASS_NONE]        = "Vulnerable",
        [SPEC_STORE_BYPASS_DISABLE]     = "Mitigation: Speculative Store Bypass disabled",
-       [SPEC_STORE_BYPASS_PRCTL]       = "Mitigation: Speculative Store Bypass disabled via prctl"
+       [SPEC_STORE_BYPASS_PRCTL]       = "Mitigation: Speculative Store Bypass disabled via prctl",
+       [SPEC_STORE_BYPASS_SECCOMP]     = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp",
 };
 
 static const struct {
        const char *option;
        enum ssb_mitigation_cmd cmd;
 } ssb_mitigation_options[] = {
-       { "auto",       SPEC_STORE_BYPASS_CMD_AUTO },  /* Platform decides */
-       { "on",         SPEC_STORE_BYPASS_CMD_ON },    /* Disable Speculative Store Bypass */
-       { "off",        SPEC_STORE_BYPASS_CMD_NONE },  /* Don't touch Speculative Store Bypass */
-       { "prctl",      SPEC_STORE_BYPASS_CMD_PRCTL }, /* Disable Speculative Store Bypass via prctl */
+       { "auto",       SPEC_STORE_BYPASS_CMD_AUTO },    /* Platform decides */
+       { "on",         SPEC_STORE_BYPASS_CMD_ON },      /* Disable Speculative Store Bypass */
+       { "off",        SPEC_STORE_BYPASS_CMD_NONE },    /* Don't touch Speculative Store Bypass */
+       { "prctl",      SPEC_STORE_BYPASS_CMD_PRCTL },   /* Disable Speculative Store Bypass via prctl */
+       { "seccomp",    SPEC_STORE_BYPASS_CMD_SECCOMP }, /* Disable Speculative Store Bypass via prctl and seccomp */
 };
 
 static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
@@ -440,8 +443,15 @@ static enum ssb_mitigation_cmd __init __ssb_select_mitigation(void)
 
        switch (cmd) {
        case SPEC_STORE_BYPASS_CMD_AUTO:
-               /* Choose prctl as the default mode */
-               mode = SPEC_STORE_BYPASS_PRCTL;
+       case SPEC_STORE_BYPASS_CMD_SECCOMP:
+               /*
+                * Choose prctl+seccomp as the default mode if seccomp is
+                * enabled.
+                */
+               if (IS_ENABLED(CONFIG_SECCOMP))
+                       mode = SPEC_STORE_BYPASS_SECCOMP;
+               else
+                       mode = SPEC_STORE_BYPASS_PRCTL;
                break;
        case SPEC_STORE_BYPASS_CMD_ON:
                mode = SPEC_STORE_BYPASS_DISABLE;
@@ -489,12 +499,14 @@ static void ssb_select_mitigation()
 }
 
 #undef pr_fmt
+#define pr_fmt(fmt)     "Speculation prctl: " fmt
 
 static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
 {
        bool update;
 
-       if (ssb_mode != SPEC_STORE_BYPASS_PRCTL)
+       if (ssb_mode != SPEC_STORE_BYPASS_PRCTL &&
+           ssb_mode != SPEC_STORE_BYPASS_SECCOMP)
                return -ENXIO;
 
        switch (ctrl) {
@@ -542,7 +554,8 @@ int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
 #ifdef CONFIG_SECCOMP
 void arch_seccomp_spec_mitigate(struct task_struct *task)
 {
-       ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
+       if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP)
+               ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
 }
 #endif
 
@@ -551,6 +564,7 @@ static int ssb_prctl_get(struct task_struct *task)
        switch (ssb_mode) {
        case SPEC_STORE_BYPASS_DISABLE:
                return PR_SPEC_DISABLE;
+       case SPEC_STORE_BYPASS_SECCOMP:
        case SPEC_STORE_BYPASS_PRCTL:
                if (task_spec_ssb_force_disable(task))
                        return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;