From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0851D2C9D for ; Tue, 30 Nov 2021 11:46:06 +0000 (UTC) Received: by mail-wm1-f73.google.com with SMTP id n41-20020a05600c502900b003335ab97f41so12710521wmr.3 for ; Tue, 30 Nov 2021 03:46:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=ykQMG7f7HitTY02bjgroWOqQwac8nTYOVAZLqTXm/og=; b=qfKYXOVzY2MTzD2zIwUpOpLCYIanN5AfAyzY4pD6y/00NCNsZhMgCXyQuHgqHRjMQP 2Q4GpB2kKiA9NG+mxwbdwhx/T6uztpsr0cPDZKwOOV4NBkpo8wKmqUMwj6QIZ50+WTGC rj+XujQ6x15SViviNrLc8ryKZTpDmfQ59NmqPKusALt7vIXW09vUdxRhx/IHgX0O1Fi0 peXM6+tWJqwR46RttMZspmzxuv6mgkZjTPQRNEx0+Evh/SfhzkOebPUPea948l/PAD60 8d8gkegUNMa+NHH1FPVvEqF67z8VdDW4GAXutQLRg58SDKDe/Mh9BClDvEsEpsff6SiM sbTA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=ykQMG7f7HitTY02bjgroWOqQwac8nTYOVAZLqTXm/og=; b=nrygsv9veV7AEYshVIX7mwa+MYUpwn9OLTtWH88bKin4DvPvNFqz5nFLM3SgZ8WgC1 KEifAtNxZEWVWhNSLBciPMsfxsg2pfcGxH9sCfA61qZYM2L4czWdSf4Mku06DjfeYGZB LIIaNMR+smkHRbqWZebkk1zBPAJm4uGV3cGFsOy6sEQOILrmgPzX/pk7pMb4s4ytaCId hhhPw6+5dfzntYT9A1ydUwL/UMIjzurfW+LhAo4Fv+L6ts/3tGYzPuk4XBUPiUTyhSob IIv0C8CKE657g4x+rjLg9QLFCozbgu7bSKaf7VgqqmuG6AjIs6BRt68JGcsyvnZ8omKW BgIw== X-Gm-Message-State: AOAM531QyvmMUihpAFZB5eqfVP1iJ30LE3Hfyt6Oi6ByaAttW8SJOSPM 3ExE2G4K6cNY0wjOGTY1EKZNNuwHjw== X-Google-Smtp-Source: ABdhPJw6whH8Hls3EC+BgAy91BvIDfMtsebOG9cJCkHwE7EfRIVxArLwzYtCPhRhlBjkro/EFip+BpGtoQ== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:86b7:11e9:7797:99f0]) (user=elver job=sendgmr) by 2002:a05:600c:4f0b:: with SMTP id l11mr626212wmq.0.1638272763966; Tue, 30 Nov 2021 03:46:03 -0800 (PST) Date: Tue, 30 Nov 2021 12:44:33 +0100 In-Reply-To: <20211130114433.2580590-1-elver@google.com> Message-Id: <20211130114433.2580590-26-elver@google.com> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20211130114433.2580590-1-elver@google.com> X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH v3 25/25] kcsan: Support WEAK_MEMORY with Clang where no objtool support exists From: Marco Elver To: elver@google.com, "Paul E. McKenney" Cc: Alexander Potapenko , Boqun Feng , Borislav Petkov , Dmitry Vyukov , Ingo Molnar , Mark Rutland , Peter Zijlstra , Thomas Gleixner , Waiman Long , Will Deacon , kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, x86@kernel.org Content-Type: text/plain; charset="UTF-8" Clang and GCC behave a little differently when it comes to the __no_sanitize_thread attribute, which has valid reasons, and depending on context either one could be right. Traditionally, user space ThreadSanitizer [1] still expects instrumented builtin atomics (to avoid false positives) and __tsan_func_{entry,exit} (to generate meaningful stack traces), even if the function has the attribute no_sanitize("thread"). [1] https://clang.llvm.org/docs/ThreadSanitizer.html#attribute-no-sanitize-thread GCC doesn't follow the same policy (for better or worse), and removes all kinds of instrumentation if no_sanitize is added. Arguably, since this may be a problem for user space ThreadSanitizer, we expect this may change in future. Since KCSAN != ThreadSanitizer, the likelihood of false positives even without barrier instrumentation everywhere, is much lower by design. At least for Clang, however, to fully remove all sanitizer instrumentation, we must add the disable_sanitizer_instrumentation attribute, which is available since Clang 14.0. Signed-off-by: Marco Elver --- v3: * New patch. --- include/linux/compiler_types.h | 13 ++++++++++++- lib/Kconfig.kcsan | 2 +- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 1d32f4c03c9e..3c1795fdb568 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -198,9 +198,20 @@ struct ftrace_likely_data { # define __no_kasan_or_inline __always_inline #endif -#define __no_kcsan __no_sanitize_thread #ifdef __SANITIZE_THREAD__ +/* + * Clang still emits instrumentation for __tsan_func_{entry,exit}() and builtin + * atomics even with __no_sanitize_thread (to avoid false positives in userspace + * ThreadSanitizer). The kernel's requirements are stricter and we really do not + * want any instrumentation with __no_kcsan. + * + * Therefore we add __disable_sanitizer_instrumentation where available to + * disable all instrumentation. See Kconfig.kcsan where this is mandatory. + */ +# define __no_kcsan __no_sanitize_thread __disable_sanitizer_instrumentation # define __no_sanitize_or_inline __no_kcsan notrace __maybe_unused +#else +# define __no_kcsan #endif #ifndef __no_sanitize_or_inline diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan index e4394ea8068b..63b70b8c5551 100644 --- a/lib/Kconfig.kcsan +++ b/lib/Kconfig.kcsan @@ -198,7 +198,7 @@ config KCSAN_WEAK_MEMORY # We can either let objtool nop __tsan_func_{entry,exit}() and builtin # atomics instrumentation in .noinstr.text, or use a compiler that can # implement __no_kcsan to really remove all instrumentation. - depends on STACK_VALIDATION || CC_IS_GCC + depends on STACK_VALIDATION || CC_IS_GCC || CLANG_VERSION >= 140000 help Enable support for modeling a subset of weak memory, which allows detecting a subset of data races due to missing memory barriers. -- 2.34.0.rc2.393.gf8c9666880-goog