From: Kim Phillips <kim.phillips@amd.com>
Date: Tue, 14 Jun 2022 23:15:51 +0200
Subject: x86/bugs: Enable STIBP for JMP2RET
Git-commit: e8ec1b6e08a2102d8755ccb06fa26d540f26a2fa
Patch-mainline: Queued in tip for 5.19
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
References: bsc#1199657 CVE-2022-29900 CVE-2022-29901
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>
[ bp: No SPECTRE_V2_USER_STRICT_PREFERRED ]
Signed-off-by: Borislav Petkov <bp@suse.de>
---
Documentation/admin-guide/kernel-parameters.txt | 14 ++++--
arch/x86/kernel/cpu/bugs.c | 50 ++++++++++++++++++------
2 files changed, 48 insertions(+), 16 deletions(-)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -856,19 +856,34 @@ static enum retbleed_mitigation retbleed
static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
RETBLEED_CMD_AUTO;
+static int __ro_after_init retbleed_nosmt = false;
+
static int __init retbleed_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
- if (!strcmp(str, "off"))
- ;
- else if (!strcmp(str, "auto"))
- retbleed_cmd = RETBLEED_CMD_AUTO;
- else if (!strcmp(str, "unret"))
- retbleed_cmd = RETBLEED_CMD_UNRET;
- else
- pr_err("Unknown retbleed option (%s). Defaulting to 'auto'\n", str);
+ while (str) {
+ char *next = strchr(str, ',');
+ if (next) {
+ *next = 0;
+ next++;
+ }
+
+ if (!strcmp(str, "off")) {
+ return -EINVAL;
+ } else if (!strcmp(str, "auto")) {
+ retbleed_cmd = RETBLEED_CMD_AUTO;
+ } else if (!strcmp(str, "unret")) {
+ retbleed_cmd = RETBLEED_CMD_UNRET;
+ } else if (!strcmp(str, "nosmt")) {
+ retbleed_nosmt = true;
+ } else {
+ pr_err("Ignoring unknown retbleed option (%s).", str);
+ }
+
+ str = next;
+ }
return 0;
}
@@ -914,6 +929,10 @@ static void __init retbleed_select_mitig
setup_force_cpu_cap(X86_FEATURE_RETHUNK);
setup_force_cpu_cap(X86_FEATURE_UNRET);
+ if (!boot_cpu_has(X86_FEATURE_STIBP) &&
+ (retbleed_nosmt || cpu_mitigations_auto_nosmt()))
+ cpu_smt_disable(false);
+
if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
pr_err(RETBLEED_UNTRAIN_MSG);
@@ -1985,10 +2004,17 @@ static ssize_t srbds_show_state(char *bu
static ssize_t retbleed_show_state(char *buf)
{
- if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET &&
- (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
- boot_cpu_data.x86_vendor != X86_VENDOR_HYGON))
- return sprintf(buf, "Vulnerable: untrained return thunk on non-Zen uarch\n");
+ if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET) {
+ if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
+ boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
+ return sprintf(buf, "Vulnerable: untrained return thunk on non-Zen uarch\n");
+
+ return sprintf(buf, "%s; SMT %s\n",
+ retbleed_strings[retbleed_mitigation],
+ !sched_smt_active() ? "disabled" :
+ spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT ?
+ "enabled with STIBP protection" : "vulnerable");
+ }
return sprintf(buf, "%s\n", retbleed_strings[retbleed_mitigation]);
}
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3981,10 +3981,16 @@
Speculative Code Execution with Return Instructions)
vulnerability.
- auto - automatically select a migitation
- unret - force enable untrained return thunks,
- only effective on AMD Zen {1,2}
- based systems.
+ auto - automatically select a migitation
+ auto,nosmt - automatically select a mitigation,
+ disabling SMT if necessary for
+ the full mitigation (only on Zen1
+ and older without STIBP).
+ unret - force enable untrained return thunks,
+ only effective on AMD f15h-f17h
+ based systems.
+ unret,nosmt - like unret, will disable SMT when STIBP
+ is not available.
Selecting 'auto' will choose a mitigation method at run
time according to the CPU.