linux-kernel - [PATCH v2 2/3] x86/bugs: spectre_v2_user default mode depends on main default

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Date: Thu,  8 Feb 2024 09:45:54 -0800
From: Breno Leitao <leitao@...ian.org>
To: mingo@...hat.com,
	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>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] x86/bugs: spectre_v2_user default mode depends on main default

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.

Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 arch/x86/kernel/cpu/bugs.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0172bb0f61fe..1fe2e939c0b3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1216,9 +1216,13 @@ 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;
@@ -1231,7 +1235,7 @@ 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 +1245,8 @@ 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)
-- 
2.39.3