linux-kernel - [PATCH] ubsan: Disable UBSAN_ALIGNMENT under COMPILE

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Message-ID: <202005011433.C42EA3E2D@keescook>
Date:   Fri, 1 May 2020 14:42:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] ubsan: Disable UBSAN_ALIGNMENT under COMPILE_TEST

The documentation for UBSAN_ALIGNMENT already mentions that it should
not be used on all*config builds (and for efficient-unaligned-access
architectures), so just refactor the Kconfig to correctly implement this
so randconfigs will stop creating insane images that freak out
objtool under CONFIG_UBSAN_TRAP (due to the false positives producing
functions that never return, etc).

Reported-by: Randy Dunlap <rdunlap@...radead.org>
Link: https://lore.kernel.org/linux-next/202004231224.D6B3B650@keescook/
Fixes: 0887a7ebc977 ("ubsan: add trap instrumentation option")
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 lib/Kconfig.ubsan                                 | 15 ++++++---------
 .../testing/selftests/wireguard/qemu/debug.config |  1 -
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 48469c95d78e..929211039bac 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -60,18 +60,15 @@ config UBSAN_SANITIZE_ALL
 	  Enabling this option will get kernel image size increased
 	  significantly.
 
-config UBSAN_NO_ALIGNMENT
-	bool "Disable checking of pointers alignment"
-	default y if HAVE_EFFICIENT_UNALIGNED_ACCESS
+config UBSAN_ALIGNMENT
+	bool "Enable checks for pointers alignment"
+	default !HAVE_EFFICIENT_UNALIGNED_ACCESS
+	depends on !X86 || !COMPILE_TEST
 	help
-	  This option disables the check of unaligned memory accesses.
-	  This option should be used when building allmodconfig.
-	  Disabling this option on architectures that support unaligned
+	  This option enables the check of unaligned memory accesses.
+	  Enabling this option on architectures that support unaligned
 	  accesses may produce a lot of false positives.
 
-config UBSAN_ALIGNMENT
-	def_bool !UBSAN_NO_ALIGNMENT
-
 config TEST_UBSAN
 	tristate "Module for testing for undefined behavior detection"
 	depends on m
diff --git a/tools/testing/selftests/wireguard/qemu/debug.config b/tools/testing/selftests/wireguard/qemu/debug.config
index 807fa7dc60b8..b50c2085c1ac 100644
--- a/tools/testing/selftests/wireguard/qemu/debug.config
+++ b/tools/testing/selftests/wireguard/qemu/debug.config
@@ -25,7 +25,6 @@ CONFIG_KASAN=y
 CONFIG_KASAN_INLINE=y
 CONFIG_UBSAN=y
 CONFIG_UBSAN_SANITIZE_ALL=y
-CONFIG_UBSAN_NO_ALIGNMENT=y
 CONFIG_UBSAN_NULL=y
 CONFIG_DEBUG_KMEMLEAK=y
 CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE=8192
-- 
2.20.1


-- 
Kees Cook