linux-kernel - [PATCH stable] Revert "x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE

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Message-Id: <20250620-stable_revert_66-v1-1-841800dd2c68@debian.org>
Date: Fri, 20 Jun 2025 06:51:23 -0700
From: Breno Leitao <leitao@...ian.org>
To: Jonathan Corbet <corbet@....net>, 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>, stable@...r.kernel.org
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 kernel-team@...a.com, David.Kaplan@....com, mingo@...nel.org, 
 brad.spengler@...nsrcsec.com, Brad Spengler <brad.spengler@...nsrcsec.com>, 
 Salvatore Bonaccorso <carnil@...ian.org>, Breno Leitao <leitao@...ian.org>
Subject: [PATCH stable] Revert "x86/bugs: Make spectre user default depend
 on MITIGATION_SPECTRE_V2" on v6.6 and older

This reverts commit 7adb96687ce8819de5c7bb172c4eeb6e45736e06.

commit 7adb96687ce8 ("x86/bugs: Make spectre user default depend on
MITIGATION_SPECTRE_V2") depends on commit 72c70f480a70 ("x86/bugs: Add
a separate config for Spectre V2"), which introduced
MITIGATION_SPECTRE_V2.

commit 72c70f480a70 ("x86/bugs: Add a separate config for Spectre V2")
never landed in stable tree, thus, stable tree doesn't have
MITIGATION_SPECTRE_V2, that said, commit 7adb96687ce8 ("x86/bugs: Make
spectre user default depend on MITIGATION_SPECTRE_V2") has no value if
the dependecy was not applied.

Revert commit 7adb96687ce8 ("x86/bugs: Make spectre user default
depend on MITIGATION_SPECTRE_V2")  in stable kernel which landed in in
5.4.294, 5.10.238, 5.15.185, 6.1.141 and 6.6.93 stable versions.

Cc: David.Kaplan@....com
Cc: peterz@...radead.org
Cc: pawan.kumar.gupta@...ux.intel.com
Cc: mingo@...nel.org
Cc: brad.spengler@...nsrcsec.com
Cc: stable@...r.kernel.org # 6.6 6.1 5.15 5.10 5.4
Reported-by: Brad Spengler <brad.spengler@...nsrcsec.com>
Reported-by: Salvatore Bonaccorso <carnil@...ian.org>
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
PS: This patch is only for stable (6.6 and older).
---
 Documentation/admin-guide/kernel-parameters.txt |  2 --
 arch/x86/kernel/cpu/bugs.c                      | 10 +++-------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 315a817e33804..f95734ceb82b8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5978,8 +5978,6 @@

 			Selecting 'on' will also enable the mitigation
 			against user space to user space task attacks.
-			Selecting specific mitigation does not force enable
-			user mitigations.

 			Selecting 'off' will disable both the kernel and
 			the user space protections.
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index e9c4bcb38f458..07b45bbf6348d 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1442,13 +1442,9 @@ static __ro_after_init enum spectre_v2_mitigation_cmd spectre_v2_cmd;
 static enum spectre_v2_user_cmd __init
 spectre_v2_parse_user_cmdline(void)
 {
-	enum spectre_v2_user_cmd mode;
 	char arg[20];
 	int ret, i;

-	mode = IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2) ?
-		SPECTRE_V2_USER_CMD_AUTO : SPECTRE_V2_USER_CMD_NONE;
-
 	switch (spectre_v2_cmd) {
 	case SPECTRE_V2_CMD_NONE:
 		return SPECTRE_V2_USER_CMD_NONE;
@@ -1461,7 +1457,7 @@ spectre_v2_parse_user_cmdline(void)
 	ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
 				  arg, sizeof(arg));
 	if (ret < 0)
-		return mode;
+		return SPECTRE_V2_USER_CMD_AUTO;

 	for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) {
 		if (match_option(arg, ret, v2_user_options[i].option)) {
@@ -1471,8 +1467,8 @@ spectre_v2_parse_user_cmdline(void)
 		}
 	}

-	pr_err("Unknown user space protection option (%s). Switching to default\n", arg);
-	return mode;
+	pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg);
+	return SPECTRE_V2_USER_CMD_AUTO;
 }

 static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)

---
base-commit: 6282921b6825fef6a1243e1c80063421d41e2576
change-id: 20250620-stable_revert_66-092ba4e66bec
prerequisite-change-id: 20250620-stable_revert-1809dd16f554:v1

Best regards,
--  
Breno Leitao <leitao@...ian.org>