Enable overflow checks by default and for release builds in the CI

Size does not increase much:

       text    data     bss      dec
    7464833 1492128 2301996 11258957 vmlinux (without Rust support)
    7667127 1701060 2301996 11670183 vmlinux (with    Rust support)
    7667127 1709252 2301996 11678375 vmlinux (+ overflow checks)

Performance is harder to measure at the time being, since we do not
have yet proper benchmarks, but we can always disable later.

Suggested-by: Kees Cook <keescook@chromium.org>
Suggested-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

.github/workflows/kernel-arm64-release.config

@@ -1375,7 +1375,7 @@ CONFIG_CC_HAS_SANCOV_TRACE_PC=y
 # Rust hacking
 #
 # CONFIG_RUST_DEBUG_ASSERTIONS is not set
-# CONFIG_RUST_OVERFLOW_CHECKS is not set
+CONFIG_RUST_OVERFLOW_CHECKS=y
 CONFIG_RUST_OPT_LEVEL_SIMILAR_AS_CHOSEN_FOR_C=y
 # CONFIG_RUST_OPT_LEVEL_0 is not set
 # CONFIG_RUST_OPT_LEVEL_1 is not set

.github/workflows/kernel-ppc64le-release.config

@@ -1483,7 +1483,7 @@ CONFIG_CC_HAS_SANCOV_TRACE_PC=y
 # Rust hacking
 #
 # CONFIG_RUST_DEBUG_ASSERTIONS is not set
-# CONFIG_RUST_OVERFLOW_CHECKS is not set
+CONFIG_RUST_OVERFLOW_CHECKS=y
 CONFIG_RUST_OPT_LEVEL_SIMILAR_AS_CHOSEN_FOR_C=y
 # CONFIG_RUST_OPT_LEVEL_0 is not set
 # CONFIG_RUST_OPT_LEVEL_1 is not set

.github/workflows/kernel-x86_64-release.config

@@ -1425,7 +1425,7 @@ CONFIG_CC_HAS_SANCOV_TRACE_PC=y
 # Rust hacking
 #
 # CONFIG_RUST_DEBUG_ASSERTIONS is not set
-# CONFIG_RUST_OVERFLOW_CHECKS is not set
+CONFIG_RUST_OVERFLOW_CHECKS=y
 CONFIG_RUST_OPT_LEVEL_SIMILAR_AS_CHOSEN_FOR_C=y
 # CONFIG_RUST_OPT_LEVEL_0 is not set
 # CONFIG_RUST_OPT_LEVEL_1 is not set

lib/Kconfig.debug

@@ -2557,7 +2557,7 @@ config RUST_DEBUG_ASSERTIONS
 
 config RUST_OVERFLOW_CHECKS
 	bool "Overflow checks"
-	default n
+	default y
 	depends on RUST
 	help
 	  Enables rustc's `-Coverflow-checks` codegen option.
@@ -2568,7 +2568,7 @@ config RUST_OVERFLOW_CHECKS
 
 	  Note that this will apply to all Rust code, including `core`.
 
-	  If unsure, say N.
+	  If unsure, say Y.
 
 choice
 	prompt "Optimization level"