linux-kernel - [PATCH 2/3] x86/bugs: Use IBPB for retbleed if used by SRSO

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250625155805.600376-3-david.kaplan@amd.com>
Date: Wed, 25 Jun 2025 10:58:04 -0500
From: David Kaplan <david.kaplan@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/3] x86/bugs: Use IBPB for retbleed if used by SRSO

If spec_rstack_overflow=ibpb then this mitigates retbleed as well.  This
is relevant for Zen1 and Zen2 CPUs which are vulnerable to both bugs.

Signed-off-by: David Kaplan <david.kaplan@....com>
Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/kernel/cpu/bugs.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6c991afb7b78..b26341983230 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1171,6 +1171,21 @@ static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
 
 static int __ro_after_init retbleed_nosmt = false;
 
+enum srso_mitigation {
+	SRSO_MITIGATION_NONE,
+	SRSO_MITIGATION_AUTO,
+	SRSO_MITIGATION_UCODE_NEEDED,
+	SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
+	SRSO_MITIGATION_MICROCODE,
+	SRSO_MITIGATION_NOSMT,
+	SRSO_MITIGATION_SAFE_RET,
+	SRSO_MITIGATION_IBPB,
+	SRSO_MITIGATION_IBPB_ON_VMEXIT,
+	SRSO_MITIGATION_BP_SPEC_REDUCE,
+};
+
+static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
+
 static int __init retbleed_parse_cmdline(char *str)
 {
 	if (!str)
@@ -1280,6 +1295,10 @@ static void __init retbleed_update_mitigation(void)
 	if (its_mitigation == ITS_MITIGATION_RETPOLINE_STUFF)
 		retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
 
+	/* If SRSO is using IBPB, that works for retbleed too */
+	if (srso_mitigation == SRSO_MITIGATION_IBPB)
+		retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+
 	if (retbleed_mitigation == RETBLEED_MITIGATION_STUFF &&
 	    !cdt_possible(spectre_v2_enabled)) {
 		pr_err("WARNING: retbleed=stuff depends on retpoline\n");
@@ -2845,19 +2864,6 @@ early_param("l1tf", l1tf_cmdline);
 #undef pr_fmt
 #define pr_fmt(fmt)	"Speculative Return Stack Overflow: " fmt
 
-enum srso_mitigation {
-	SRSO_MITIGATION_NONE,
-	SRSO_MITIGATION_AUTO,
-	SRSO_MITIGATION_UCODE_NEEDED,
-	SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
-	SRSO_MITIGATION_MICROCODE,
-	SRSO_MITIGATION_NOSMT,
-	SRSO_MITIGATION_SAFE_RET,
-	SRSO_MITIGATION_IBPB,
-	SRSO_MITIGATION_IBPB_ON_VMEXIT,
-	SRSO_MITIGATION_BP_SPEC_REDUCE,
-};
-
 static const char * const srso_strings[] = {
 	[SRSO_MITIGATION_NONE]			= "Vulnerable",
 	[SRSO_MITIGATION_UCODE_NEEDED]		= "Vulnerable: No microcode",
@@ -2870,8 +2876,6 @@ static const char * const srso_strings[] = {
 	[SRSO_MITIGATION_BP_SPEC_REDUCE]	= "Mitigation: Reduced Speculation"
 };
 
-static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
-
 static int __init srso_parse_cmdline(char *str)
 {
 	if (!str)
-- 
2.34.1