Make it clearer in the one-line description and the verbose description
text that CONFIG_UBSAN_TRAP as currently implemented involves a tradeoff of
much less helpful oops messages in exchange for a smaller kernel image.
(With the additional effect of turning UBSAN warnings into crashes, which
may or may not be desired.)

Signed-off-by: Jann Horn <jannh@google.com>
---
 lib/Kconfig.ubsan | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index efae7e011956..e4f19ba9a029 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -13,7 +13,7 @@ menuconfig UBSAN
 if UBSAN
 
 config UBSAN_TRAP
-	bool "On Sanitizer warnings, abort the running kernel code"
+	bool "Abort on Sanitizer warnings (smaller kernel but less verbose)"
 	depends on !COMPILE_TEST
 	help
 	  Building kernels with Sanitizer features enabled tends to grow
@@ -26,6 +26,14 @@ config UBSAN_TRAP
 	  the system. For some system builders this is an acceptable
 	  trade-off.
 
+	  CAUTION: Selecting Y will (depending on architecture) cause your
+	  kernel to oops with an undefined instruction error with no further
+	  details when a UBSAN violation occurs.
+	  (arm64 can show some basic information.)
+	  This may make it hard to determine whether an oops was caused by
+	  UBSAN or to figure out the details of a UBSAN violation.
+	  It makes the kernel log output less useful for bug reports.
+
 config CC_HAS_UBSAN_BOUNDS_STRICT
 	def_bool $(cc-option,-fsanitize=bounds-strict)
 	help

base-commit: d528014517f2b0531862c02865b9d4c908019dc4
-- 
2.41.0.255.g8b1d071c50-goog

On Wed, 05 Jul 2023 23:51:27 +0200, Jann Horn wrote:
> Make it clearer in the one-line description and the verbose description
> text that CONFIG_UBSAN_TRAP as currently implemented involves a tradeoff of
> much less helpful oops messages in exchange for a smaller kernel image.
> (With the additional effect of turning UBSAN warnings into crashes, which
> may or may not be desired.)
> 
> 
> [...]

Applied with some tweaks to wording, thanks!

[1/1] ubsan: Clarify Kconfig text for CONFIG_UBSAN_TRAP
      https://git.kernel.org/kees/c/a2dbac607873

-- 
Kees Cook