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 D547B29CA for ; Tue, 30 Nov 2021 11:45:11 +0000 (UTC) Received: by mail-wm1-f73.google.com with SMTP id 187-20020a1c02c4000000b003335872db8dso10296421wmc.2 for ; Tue, 30 Nov 2021 03:45:11 -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=cCyxJnES0DWyrpQ2J5vRoZu9DlHTb3+fL88VjiCWbjg=; b=cKjMDTXM8NjyKwJV3lDtGCObCm4HpcJe5F+4CzZRRXVIIKSOXaY8t1H5jc/MfrMybp l7C1C5PdFSieee+5Ow4GgXoKOJzHKEgRplPyzIuWqJojZ+nN2/4IJsjhDdaZMC4hfGLc YjipwbrwuXGRJcsG9dWRqwvvUcQGiVB9s3RVhs0q+yDpoxr5r2oMHuFRBcQ1r5QIpX3k KQBK18DLneuEMmku+aWMunTXlRFji0E50ji38pRBCDpdp+D21l7U1sivA4dITmYi7DXU QeLVu19keyQA504MdNHYtGnlBTN/rI+Vy0aqov/bs8mgOaxhMmA9ff8gcphJR+tq3WW4 AyAg== 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=cCyxJnES0DWyrpQ2J5vRoZu9DlHTb3+fL88VjiCWbjg=; b=u8u65ebEDYeC+N0wEVzv675emGKayrQTtByVfk353vO4fLKerlNThLaooAYW2QvjyF POwvzP4tyGel4JPFXpGwuwlaSUZRn7joFFzKRo2a8zjePjiy7cLuvD3ZTCqlfkqaqR5S 4munK+msoOaDsMJedHMkKD+ugqSYXZ4aWAdXd6+jkY2r3sRMG60N0M69rqDC0T/Qffqh iXuUswRsGNpGDVRA3U2wOKLctcT5JrpVK4KWPJ9eVbw6LDgYconp0nJ8FdIkxjS9quPc xUoyOJyPww8zRBlzzrb3MZk0OJdgG09E9qxPii1NxuWsevzYUhMNGTt3wZAZIYE8l75b xGdA== X-Gm-Message-State: AOAM533GznXWDzhCnTdFYqQW8BiUdvQ3CC4gDfxMosVUlWltYE6otYDi 7uh/0UoFgByRyLWL+nGwUJIVHAYNfA== X-Google-Smtp-Source: ABdhPJz78uHZ/XMYdk54D/l9GyDkbV5tPc83Pq6RQwiWk9kg5EHHGLp650DVfz5FKzeodb/NW5W0kpyZ5g== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:86b7:11e9:7797:99f0]) (user=elver job=sendgmr) by 2002:a05:600c:1d1b:: with SMTP id l27mr623895wms.1.1638272709978; Tue, 30 Nov 2021 03:45:09 -0800 (PST) Date: Tue, 30 Nov 2021 12:44:11 +0100 In-Reply-To: <20211130114433.2580590-1-elver@google.com> Message-Id: <20211130114433.2580590-4-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 03/25] kcsan: Avoid checking scoped accesses from nested contexts 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" Avoid checking scoped accesses from nested contexts (such as nested interrupts or in scheduler code) which share the same kcsan_ctx. This is to avoid detecting false positive races of accesses in the same thread with currently scoped accesses: consider setting up a watchpoint for a non-scoped (normal) access that also "conflicts" with a current scoped access. In a nested interrupt (or in the scheduler), which shares the same kcsan_ctx, we cannot check scoped accesses set up in the parent context -- simply ignore them in this case. With the introduction of kcsan_ctx::disable_scoped, we can also clean up kcsan_check_scoped_accesses()'s recursion guard, and do not need to modify the list's prev pointer. Signed-off-by: Marco Elver --- include/linux/kcsan.h | 1 + kernel/kcsan/core.c | 18 +++++++++++++++--- 2 files changed, 16 insertions(+), 3 deletions(-) diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h index fc266ecb2a4d..13cef3458fed 100644 --- a/include/linux/kcsan.h +++ b/include/linux/kcsan.h @@ -21,6 +21,7 @@ */ struct kcsan_ctx { int disable_count; /* disable counter */ + int disable_scoped; /* disable scoped access counter */ int atomic_next; /* number of following atomic ops */ /* diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index e34a1710b7bc..bd359f8ee63a 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -204,15 +204,17 @@ check_access(const volatile void *ptr, size_t size, int type, unsigned long ip); static noinline void kcsan_check_scoped_accesses(void) { struct kcsan_ctx *ctx = get_ctx(); - struct list_head *prev_save = ctx->scoped_accesses.prev; struct kcsan_scoped_access *scoped_access; - ctx->scoped_accesses.prev = NULL; /* Avoid recursion. */ + if (ctx->disable_scoped) + return; + + ctx->disable_scoped++; list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) { check_access(scoped_access->ptr, scoped_access->size, scoped_access->type, scoped_access->ip); } - ctx->scoped_accesses.prev = prev_save; + ctx->disable_scoped--; } /* Rules for generic atomic accesses. Called from fast-path. */ @@ -465,6 +467,15 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned goto out; } + /* + * Avoid races of scoped accesses from nested interrupts (or scheduler). + * Assume setting up a watchpoint for a non-scoped (normal) access that + * also conflicts with a current scoped access. In a nested interrupt, + * which shares the context, it would check a conflicting scoped access. + * To avoid, disable scoped access checking. + */ + ctx->disable_scoped++; + /* * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's * runtime is entered for every memory access, and potentially useful @@ -578,6 +589,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned if (!kcsan_interrupt_watcher) local_irq_restore(irq_flags); kcsan_restore_irqtrace(current); + ctx->disable_scoped--; out: user_access_restore(ua_flags); } -- 2.34.0.rc2.393.gf8c9666880-goog