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x86/bugs: Enable STIBP for JMP2RET
For untrained return thunks to be fully effective, STIBP must be enabled or SMT disabled. Co-developed-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Kim Phillips <kim.phillips@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Borislav Petkov <bp@suse.de>
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2 changed files with 57 additions and 17 deletions
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@ -5201,11 +5201,17 @@
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Speculative Code Execution with Return Instructions)
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Speculative Code Execution with Return Instructions)
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vulnerability.
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vulnerability.
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off - unconditionally disable
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off - no mitigation
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auto - automatically select a migitation
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auto - automatically select a migitation
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unret - force enable untrained return thunks,
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auto,nosmt - automatically select a mitigation,
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only effective on AMD Zen {1,2}
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disabling SMT if necessary for
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based systems.
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the full mitigation (only on Zen1
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and older without STIBP).
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unret - force enable untrained return thunks,
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only effective on AMD f15h-f17h
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based systems.
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unret,nosmt - like unret, will disable SMT when STIBP
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is not available.
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Selecting 'auto' will choose a mitigation method at run
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Selecting 'auto' will choose a mitigation method at run
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time according to the CPU.
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time according to the CPU.
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@ -783,19 +783,34 @@ static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
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static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
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static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
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RETBLEED_CMD_AUTO;
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RETBLEED_CMD_AUTO;
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static int __ro_after_init retbleed_nosmt = false;
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static int __init retbleed_parse_cmdline(char *str)
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static int __init retbleed_parse_cmdline(char *str)
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{
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{
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if (!str)
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if (!str)
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return -EINVAL;
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return -EINVAL;
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if (!strcmp(str, "off"))
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while (str) {
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retbleed_cmd = RETBLEED_CMD_OFF;
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char *next = strchr(str, ',');
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else if (!strcmp(str, "auto"))
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if (next) {
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retbleed_cmd = RETBLEED_CMD_AUTO;
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*next = 0;
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else if (!strcmp(str, "unret"))
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next++;
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retbleed_cmd = RETBLEED_CMD_UNRET;
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}
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else
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pr_err("Unknown retbleed option (%s). Defaulting to 'auto'\n", str);
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if (!strcmp(str, "off")) {
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retbleed_cmd = RETBLEED_CMD_OFF;
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} else if (!strcmp(str, "auto")) {
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retbleed_cmd = RETBLEED_CMD_AUTO;
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} else if (!strcmp(str, "unret")) {
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retbleed_cmd = RETBLEED_CMD_UNRET;
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} else if (!strcmp(str, "nosmt")) {
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retbleed_nosmt = true;
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} else {
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pr_err("Ignoring unknown retbleed option (%s).", str);
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}
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str = next;
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}
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return 0;
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return 0;
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}
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}
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@ -841,6 +856,10 @@ static void __init retbleed_select_mitigation(void)
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setup_force_cpu_cap(X86_FEATURE_RETHUNK);
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setup_force_cpu_cap(X86_FEATURE_RETHUNK);
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setup_force_cpu_cap(X86_FEATURE_UNRET);
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setup_force_cpu_cap(X86_FEATURE_UNRET);
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if (!boot_cpu_has(X86_FEATURE_STIBP) &&
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(retbleed_nosmt || cpu_mitigations_auto_nosmt()))
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cpu_smt_disable(false);
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if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
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if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
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boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
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boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
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pr_err(RETBLEED_UNTRAIN_MSG);
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pr_err(RETBLEED_UNTRAIN_MSG);
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@ -1087,6 +1106,13 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
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boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
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boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
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mode = SPECTRE_V2_USER_STRICT_PREFERRED;
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mode = SPECTRE_V2_USER_STRICT_PREFERRED;
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if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET) {
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if (mode != SPECTRE_V2_USER_STRICT &&
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mode != SPECTRE_V2_USER_STRICT_PREFERRED)
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pr_info("Selecting STIBP always-on mode to complement retbleed mitigation'\n");
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mode = SPECTRE_V2_USER_STRICT_PREFERRED;
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}
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spectre_v2_user_stibp = mode;
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spectre_v2_user_stibp = mode;
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set_mode:
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set_mode:
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@ -2097,10 +2123,18 @@ static ssize_t srbds_show_state(char *buf)
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static ssize_t retbleed_show_state(char *buf)
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static ssize_t retbleed_show_state(char *buf)
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{
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{
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if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET &&
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if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET) {
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(boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
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if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
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boot_cpu_data.x86_vendor != X86_VENDOR_HYGON))
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boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
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return sprintf(buf, "Vulnerable: untrained return thunk on non-Zen uarch\n");
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return sprintf(buf, "Vulnerable: untrained return thunk on non-Zen uarch\n");
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return sprintf(buf, "%s; SMT %s\n",
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retbleed_strings[retbleed_mitigation],
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!sched_smt_active() ? "disabled" :
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spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT ||
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spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED ?
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"enabled with STIBP protection" : "vulnerable");
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}
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return sprintf(buf, "%s\n", retbleed_strings[retbleed_mitigation]);
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return sprintf(buf, "%s\n", retbleed_strings[retbleed_mitigation]);
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}
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}
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