linux-kernel - [PATCH] kcov: fix generic Kconfig dependencies if ARCH_WANTS_NO

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Message-Id: <20211201152604.3984495-1-elver@google.com>
Date:   Wed,  1 Dec 2021 16:26:04 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kasan-dev@...glegroups.com,
        Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] kcov: fix generic Kconfig dependencies if ARCH_WANTS_NO_INSTR

Until recent versions of GCC and Clang, it was not possible to disable
KCOV instrumentation via a function attribute. The relevant function
attribute was introduced in 540540d06e9d9 ("kcov: add
__no_sanitize_coverage to fix noinstr for all architectures").

x86 was the first architecture to want a working noinstr, and at the
time no compiler support for the attribute existed yet. Therefore,
0f1441b44e823 ("objtool: Fix noinstr vs KCOV") introduced the ability to
NOP __sanitizer_cov_*() calls in .noinstr.text.

However, this doesn't work for other architectures like arm64 and s390
that want a working noinstr per ARCH_WANTS_NO_INSTR.

At the time of 0f1441b44e823, we didn't yet have ARCH_WANTS_NO_INSTR,
but now we can move the Kconfig dependency checks to the generic KCOV
option. KCOV will be available if:

	- architecture does not care about noinstr, OR
	- we have objtool support (like on x86), OR
	- GCC is 12.0 or newer, OR
	- Clang is 13.0 or newer.

Signed-off-by: Marco Elver <elver@...gle.com>
---
 arch/x86/Kconfig  | 2 +-
 lib/Kconfig.debug | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 95dd1ee01546..c030b2ee93b3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -78,7 +78,7 @@ config X86
 	select ARCH_HAS_FILTER_PGPROT
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
-	select ARCH_HAS_KCOV			if X86_64 && STACK_VALIDATION
+	select ARCH_HAS_KCOV			if X86_64
 	select ARCH_HAS_MEM_ENCRYPT
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9ef7ce18b4f5..589c8aaa2d5b 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1977,6 +1977,8 @@ config KCOV
 	bool "Code coverage for fuzzing"
 	depends on ARCH_HAS_KCOV
 	depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
+	depends on !ARCH_WANTS_NO_INSTR || STACK_VALIDATION || \
+		   GCC_VERSION >= 120000 || CLANG_VERSION >= 130000
 	select DEBUG_FS
 	select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
 	help
-- 
2.34.0.rc2.393.gf8c9666880-goog