[tip: x86/core] x86/cfi: Add 'cfi=warn' boot option

tip-bot2 for Peter Zijlstra
2025-02-26T12:04:51Z

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

Commit-ID: 9a54fb31343362f93680543e37afc14484c185d9
Gitweb: https://git.kernel.org/tip/9a54fb31343362f93680543e37afc14484c185d9
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Mon, 24 Feb 2025 13:37:04 +01:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 26 Feb 2025 12:10:48 +01:00

x86/cfi: Add 'cfi=warn' boot option

Rebuilding with CONFIG_CFI_PERMISSIVE=y enabled is such a pain, esp. since
clang is so slow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.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;
}