linux-kernel - [PATCH v2] kasan: simplify and clarify Makefile

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Message-Id: <20240814161052.10374-1-andrey.konovalov@linux.dev>
Date: Wed, 14 Aug 2024 18:10:52 +0200
From: andrey.konovalov@...ux.dev
To: Marco Elver <elver@...gle.com>,
	Matthew Maurer <mmaurer@...gle.com>,
	Miguel Ojeda <ojeda@...nel.org>
Cc: Andrey Konovalov <andreyknvl@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	kasan-dev@...glegroups.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] kasan: simplify and clarify Makefile

From: Andrey Konovalov <andreyknvl@...il.com>

When KASAN support was being added to the Linux kernel, GCC did not yet
support all of the KASAN-related compiler options. Thus, the KASAN
Makefile had to probe the compiler for supported options.

Nowadays, the Linux kernel GCC version requirement is 5.1+, and thus we
don't need the probing of the -fasan-shadow-offset parameter: it exists in
all 5.1+ GCCs.

Simplify the KASAN Makefile to drop CFLAGS_KASAN_MINIMAL.

Also add a few more comments and unify the indentation.

Signed-off-by: Andrey Konovalov <andreyknvl@...il.com>

---

Changes v1->v2:
- Comments fixes based on Miguel Ojeda's feedback.
---
 scripts/Makefile.kasan | 45 +++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 390658a2d5b74..aab4154af00a7 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -22,30 +22,31 @@ endif
 ifdef CONFIG_KASAN_GENERIC
 
 ifdef CONFIG_KASAN_INLINE
+	# When the number of memory accesses in a function is less than this
+	# call threshold number, the compiler will use inline instrumentation.
+	# 10000 is chosen offhand as a sufficiently large number to make all
+	# kernel functions to be instrumented inline.
 	call_threshold := 10000
 else
 	call_threshold := 0
 endif
 
-CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address
-
-# -fasan-shadow-offset fails without -fsanitize
-CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \
-			-fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \
-			$(call cc-option, -fsanitize=kernel-address \
-			-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
-
-ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),)
-	CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
-else
-	# Now add all the compiler specific options that are valid standalone
-	CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
-	 $(call cc-param,asan-globals=1) \
-	 $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
-	 $(call cc-param,asan-instrument-allocas=1)
-endif
-
-CFLAGS_KASAN += $(call cc-param,asan-stack=$(stack_enable))
+# First, enable -fsanitize=kernel-address together with providing the shadow
+# mapping offset, as for GCC, -fasan-shadow-offset fails without -fsanitize
+# (GCC accepts the shadow mapping offset via -fasan-shadow-offset instead of
+# a --param like the other KASAN parameters).
+# Instead of ifdef-checking the compiler, rely on cc-option.
+CFLAGS_KASAN := $(call cc-option, -fsanitize=kernel-address \
+		-fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \
+		$(call cc-option, -fsanitize=kernel-address \
+		-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
+
+# Now, add other parameters enabled similarly in both GCC and Clang.
+# As some of them are not supported by older compilers, use cc-param.
+CFLAGS_KASAN += $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
+		$(call cc-param,asan-stack=$(stack_enable)) \
+		$(call cc-param,asan-instrument-allocas=1) \
+		$(call cc-param,asan-globals=1)
 
 # Instrument memcpy/memset/memmove calls by using instrumented __asan_mem*()
 # instead. With compilers that don't support this option, compiler-inserted
@@ -57,9 +58,9 @@ endif # CONFIG_KASAN_GENERIC
 ifdef CONFIG_KASAN_SW_TAGS
 
 ifdef CONFIG_KASAN_INLINE
-    instrumentation_flags := $(call cc-param,hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET))
+	instrumentation_flags := $(call cc-param,hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET))
 else
-    instrumentation_flags := $(call cc-param,hwasan-instrument-with-calls=1)
+	instrumentation_flags := $(call cc-param,hwasan-instrument-with-calls=1)
 endif
 
 CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
@@ -70,7 +71,7 @@ CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
 
 # Instrument memcpy/memset/memmove calls by using instrumented __hwasan_mem*().
 ifeq ($(call clang-min-version, 150000)$(call gcc-min-version, 130000),y)
-CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
+	CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
 endif
 
 endif # CONFIG_KASAN_SW_TAGS
-- 
2.25.1