From: Ferran Duarri <ferran.duarri@me.com>
To: Nathan Chancellor <nathan@kernel.org>, Nicolas Schier <nsc@kernel.org>
Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
Ferran Duarri <ferran.duarri@me.com>
Subject: [PATCH] kbuild: ubsan: skip UBSAN for external modules by default
Date: Thu, 20 Aug 2026 21:01:58 +0200 [thread overview]
Message-ID: <20260820190200.203185-1-ferran.duarri@me.com> (raw)
External modules built with KBUILD_EXTMOD set inherit UBSAN sanitizer
flags from the kernel's KBUILD_CFLAGS because is-kernel-object is 'y'
for any obj-m object. This silently breaks third-party modules whose
source code (e.g. VMware vmnet/vmmon) triggers UBSAN UB checks at
runtime, causing packet-forwarding failures and VM instability while
the module itself loads successfully.
Make UBSAN opt-in for external modules: skip the is-kernel-object 'y'
fallback when KBUILD_EXTMOD is set. External modules that explicitly
need UBSAN can still opt in by setting UBSAN_SANITIZE := y.
In-kernel module builds are not affected.
Signed-off-by: Ferran Duarri <ferran.duarri@me.com>
---
scripts/Makefile.lib | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0718e39cedda..393af3f970af 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -74,10 +74,10 @@ endif
ifeq ($(CONFIG_UBSAN),y)
_c_flags += $(if $(patsubst n%,, \
- $(UBSAN_SANITIZE_$(target-stem).o)$(UBSAN_SANITIZE)$(is-kernel-object)), \
+ $(UBSAN_SANITIZE_$(target-stem).o)$(UBSAN_SANITIZE)$(if $(KBUILD_EXTMOD),,$(is-kernel-object))), \
$(CFLAGS_UBSAN))
_c_flags += $(if $(patsubst n%,, \
- $(UBSAN_INTEGER_WRAP_$(target-stem).o)$(UBSAN_SANITIZE_$(target-stem).o)$(UBSAN_INTEGER_WRAP)$(UBSAN_SANITIZE)$(is-kernel-object)), \
+ $(UBSAN_INTEGER_WRAP_$(target-stem).o)$(UBSAN_SANITIZE_$(target-stem).o)$(UBSAN_INTEGER_WRAP)$(UBSAN_SANITIZE)$(if $(KBUILD_EXTMOD),,$(is-kernel-object))), \
$(CFLAGS_UBSAN_INTEGER_WRAP))
endif
next reply other threads:[~2026-08-20 19:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-20 19:01 Ferran Duarri [this message]
2026-08-21 19:07 ` [PATCH] kbuild: ubsan: skip UBSAN for external modules by default Nathan Chancellor
2026-08-21 19:52 ` Nicolas Schier
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