x86/bugs: Report Intel retbleed vulnerability

Skylake suffers from RSB underflow speculation issues; report this
vulnerability and it's mitigation (spectre_v2=ibrs).

  [jpoimboe: cleanups, eibrs]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

1 files changed, 33 insertions, 6 deletions

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c546a9e4ed17..05f29db9473b 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -790,12 +790,17 @@ static int __init nospectre_v1_cmdline(char *str)
 }
 early_param("nospectre_v1", nospectre_v1_cmdline);
 
+static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
+	SPECTRE_V2_NONE;
+
 #undef pr_fmt
 #define pr_fmt(fmt)     "RETBleed: " fmt
 
 enum retbleed_mitigation {
 	RETBLEED_MITIGATION_NONE,
 	RETBLEED_MITIGATION_UNRET,
+	RETBLEED_MITIGATION_IBRS,
+	RETBLEED_MITIGATION_EIBRS,
 };
 
 enum retbleed_mitigation_cmd {
@@ -807,6 +812,8 @@ enum retbleed_mitigation_cmd {
 const char * const retbleed_strings[] = {
 	[RETBLEED_MITIGATION_NONE]	= "Vulnerable",
 	[RETBLEED_MITIGATION_UNRET]	= "Mitigation: untrained return thunk",
+	[RETBLEED_MITIGATION_IBRS]	= "Mitigation: IBRS",
+	[RETBLEED_MITIGATION_EIBRS]	= "Mitigation: Enhanced IBRS",
 };
 
 static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
@@ -849,6 +856,7 @@ early_param("retbleed", retbleed_parse_cmdline);
 
 #define RETBLEED_UNTRAIN_MSG "WARNING: BTB untrained return thunk mitigation is only effective on AMD/Hygon!\n"
 #define RETBLEED_COMPILER_MSG "WARNING: kernel not compiled with RETPOLINE or -mfunction-return capable compiler!\n"
+#define RETBLEED_INTEL_MSG "WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible!\n"
 
 static void __init retbleed_select_mitigation(void)
 {
@@ -865,12 +873,15 @@ static void __init retbleed_select_mitigation(void)
 
 	case RETBLEED_CMD_AUTO:
 	default:
-		if (!boot_cpu_has_bug(X86_BUG_RETBLEED))
-			break;
-
 		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
 		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
 			retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
+
+		/*
+		 * The Intel mitigation (IBRS) was already selected in
+		 * spectre_v2_select_mitigation().
+		 */
+
 		break;
 	}
 
@@ -900,15 +911,31 @@ static void __init retbleed_select_mitigation(void)
 		break;
 	}
 
+	/*
+	 * Let IBRS trump all on Intel without affecting the effects of the
+	 * retbleed= cmdline option.
+	 */
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
+		switch (spectre_v2_enabled) {
+		case SPECTRE_V2_IBRS:
+			retbleed_mitigation = RETBLEED_MITIGATION_IBRS;
+			break;
+		case SPECTRE_V2_EIBRS:
+		case SPECTRE_V2_EIBRS_RETPOLINE:
+		case SPECTRE_V2_EIBRS_LFENCE:
+			retbleed_mitigation = RETBLEED_MITIGATION_EIBRS;
+			break;
+		default:
+			pr_err(RETBLEED_INTEL_MSG);
+		}
+	}
+
 	pr_info("%s\n", retbleed_strings[retbleed_mitigation]);
 }
 
 #undef pr_fmt
 #define pr_fmt(fmt)     "Spectre V2 : " fmt
 
-static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
-	SPECTRE_V2_NONE;
-
 static enum spectre_v2_user_mitigation spectre_v2_user_stibp __ro_after_init =
 	SPECTRE_V2_USER_NONE;
 static enum spectre_v2_user_mitigation spectre_v2_user_ibpb __ro_after_init =