linux-kernel - [tip: x86/core] x86/cfi: Add warn option

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Message-ID: <174056726322.10177.14430365702785340054.tip-bot2@tip-bot2>
Date: Wed, 26 Feb 2025 10:54:23 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Kees Cook <kees@...nel.org>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/core] x86/cfi: Add warn option

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     f003da5d29a179bd1beb4ef87ac93a3ca6ddf734
Gitweb:        https://git.kernel.org/tip/f003da5d29a179bd1beb4ef87ac93a3ca6ddf734
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 24 Feb 2025 13:37:04 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 26 Feb 2025 11:41:53 +01:00

x86/cfi: Add warn option

Rebuilding with CFI_PERMISSIVE toggled is such a pain, esp. since
clang is so slow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Kees Cook <kees@...nel.org>
Link: https://lore.kernel.org/r/20250224124159.924496481@infradead.org
---
 arch/x86/kernel/alternative.c | 3 +++
 include/linux/cfi.h           | 2 ++
 kernel/cfi.c                  | 4 +++-
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 247ee5f..1142ebd 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1022,6 +1022,9 @@ static __init int cfi_parse_cmdline(char *str)
 			cfi_mode = CFI_FINEIBT;
 		} else if (!strcmp(str, "norand")) {
 			cfi_rand = false;
+		} else if (!strcmp(str, "warn")) {
+			pr_alert("CFI mismatch non-fatal!\n");
+			cfi_warn = true;
 		} else {
 			pr_err("Ignoring unknown cfi option (%s).", str);
 		}
diff --git a/include/linux/cfi.h b/include/linux/cfi.h
index f0df518..1db17ec 100644
--- a/include/linux/cfi.h
+++ b/include/linux/cfi.h
@@ -11,6 +11,8 @@
 #include <linux/module.h>
 #include <asm/cfi.h>
 
+extern bool cfi_warn;
+
 #ifndef cfi_get_offset
 static inline int cfi_get_offset(void)
 {
diff --git a/kernel/cfi.c b/kernel/cfi.c
index 08caad7..19be796 100644
--- a/kernel/cfi.c
+++ b/kernel/cfi.c
@@ -7,6 +7,8 @@
 
 #include <linux/cfi.h>
 
+bool cfi_warn __ro_after_init = IS_ENABLED(CONFIG_CFI_PERMISSIVE);
+
 enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
 				      unsigned long *target, u32 type)
 {
@@ -17,7 +19,7 @@ enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
 		pr_err("CFI failure at %pS (no target information)\n",
 		       (void *)addr);
 
-	if (IS_ENABLED(CONFIG_CFI_PERMISSIVE)) {
+	if (cfi_warn) {
 		__warn(NULL, 0, (void *)addr, 0, regs, NULL);
 		return BUG_TRAP_TYPE_WARN;
 	}