linux-kernel - [PATCH v6 12/13] x86/bugs: spectre_v2_user default mode depends on Kconfig

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Date:   Tue, 21 Nov 2023 08:07:39 -0800
From:   Breno Leitao <leitao@...ian.org>
To:     jpoimboe@...nel.org, mingo@...hat.com, tglx@...utronix.de,
        bp@...en8.de, Peter Zijlstra <peterz@...radead.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     leit@...a.com, linux-kernel@...r.kernel.org
Subject: [PATCH v6 12/13] x86/bugs: spectre_v2_user default mode depends on Kconfig

Change the default value of spectre v2 in user mode to respect the
CONFIG_MITIGATION_SPECTRE_V2 config option.

Currently, user mode spectre v2 is set to auto
(SPECTRE_V2_USER_CMD_AUTO) by default, even if
CONFIG_MITIGATION_SPECTRE_V2 is disabled.

Set the Spectre_v2 value to auto (SPECTRE_V2_USER_CMD_AUTO) if the
Spectre v2 config (CONFIG_MITIGATION_SPECTRE_V2) is enabled, otherwise
set the value to none (SPECTRE_V2_USER_CMD_NONE).

Important to say the command line argument "spectre_v2_user" overwrites
the default value in both cases.

Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 arch/x86/kernel/cpu/bugs.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0172bb0f61fe..a99f8c064682 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1216,8 +1216,11 @@ 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)
 {
+	int ret, i, 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:
@@ -1231,7 +1234,7 @@ spectre_v2_parse_user_cmdline(void)
 	ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
 				  arg, sizeof(arg));
 	if (ret < 0)
-		return SPECTRE_V2_USER_CMD_AUTO;
+		return mode;
 
 	for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) {
 		if (match_option(arg, ret, v2_user_options[i].option)) {
@@ -1241,8 +1244,8 @@ spectre_v2_parse_user_cmdline(void)
 		}
 	}
 
-	pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg);
-	return SPECTRE_V2_USER_CMD_AUTO;
+	pr_err("Unknown user space protection option (%s). Switching to default\n", arg);
+	return mode;
 }
 
 static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
-- 
2.34.1