From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E39ECA9EB0 for ; Mon, 21 Oct 2019 15:54:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE02D20B7C for ; Mon, 21 Oct 2019 15:54:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="rf7KtD2m" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729659AbfJUPyt (ORCPT ); Mon, 21 Oct 2019 11:54:49 -0400 Received: from mail-oi1-f195.google.com ([209.85.167.195]:37673 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729604AbfJUPyr (ORCPT ); Mon, 21 Oct 2019 11:54:47 -0400 Received: by mail-oi1-f195.google.com with SMTP id i16so11473530oie.4 for ; Mon, 21 Oct 2019 08:54:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=pX4+d7Ncjn+xn92QrhRTScOyiBqd+k+y0FQHaWJvMCM=; b=rf7KtD2mPVG6jZzHVlIhtYYic9JK9h6wHB2xNneMy994IwZ38gz72cwNZqVHkkOu9H Q6L44KQ68HfTvhYFYiamuji4sHbW5IifLkW3bB98bjWLyyxOnM8jZ5BC5BT3ARfyNvZb vIlvRYnezSmyYNDW1RhHWVbYdgpIQufBFksqLQtTOZNw4LLFkv3Qmuu0RgBoJJgbhget GCXz2XG+KZA3eGdgXOm0IwoVeZnTbDBiE9UuqRfVBHzKhrn7sl+AnUCbY1NdKlArMUUN zSlh2IT8Zftdwc9rRDaNTC6rAqHVyVDxi7EkGvumdGobku8BYGk2Hswgd4OEgzdBdBbq kecA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=pX4+d7Ncjn+xn92QrhRTScOyiBqd+k+y0FQHaWJvMCM=; b=DdxKIgfxkUQnmxccePoAFt2E/kSRBb8ePrLqfh1bDw0JJ0otiVqkhq5i3ADj4eyI73 KcC0xSSKpJGGPQXqzw6Dp96esFxNCXwLx/mVDtEVUJl6EG6MPTBdlgo0TkAhegV+z8TZ h+q3dMnEUjEpBTTeOHPgvnLNeyJy+B+d0dVhLzyoL1V55Ho1g+DtlnQWRHwHwbfE1uzb Db+FW67+aRRDqzEWtLHmhXE4XkxY7Q7uQRXxnkGAEmFWDT1xDbWPSlelon/m10ehopJ3 LkKId2f5AYutECljFCCmrOk3MlYuavhazJFBf0suIH4l8Iz2ujP6sUPkT5+qCilxLT6B O5yQ== X-Gm-Message-State: APjAAAWxD3RTF22SYca/uEd5Iyw9Nvtznzc8i3aLH9wy3on4UPfBfz/c 4wndUdZIcXHpCDudHBzFPRmp+qzcBpzVa6MVMt4BNQ== X-Google-Smtp-Source: APXvYqyKvY92EdIzPna/d3pmsp8dn2wZZI4Mxk66OBQDwJbHnIgiorxMZ2BVXh8nd/0cFFSCLw/+SoOADfTEBjjZOx4= X-Received: by 2002:aca:55cb:: with SMTP id j194mr18840866oib.155.1571673281529; Mon, 21 Oct 2019 08:54:41 -0700 (PDT) MIME-Version: 1.0 References: <20191017141305.146193-1-elver@google.com> <20191017141305.146193-2-elver@google.com> In-Reply-To: From: Marco Elver Date: Mon, 21 Oct 2019 17:54:28 +0200 Message-ID: Subject: Re: [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure To: Alexander Potapenko Cc: LKMM Maintainers -- Akira Yokosawa , Alan Stern , Andrea Parri , Andrey Konovalov , Andy Lutomirski , Ard Biesheuvel , Arnd Bergmann , Boqun Feng , Borislav Petkov , Daniel Axtens , Daniel Lustig , dave.hansen@linux.intel.com, David Howells , Dmitriy Vyukov , "H. Peter Anvin" , Ingo Molnar , Jade Alglave , Joel Fernandes , Jonathan Corbet , Josh Poimboeuf , Luc Maranget , Mark Rutland , Nicholas Piggin , Paul McKenney , Peter Zijlstra , Thomas Gleixner , Will Deacon , kasan-dev , linux-arch , "open list:DOCUMENTATION" , linux-efi@vger.kernel.org, Linux Kbuild mailing list , LKML , Linux Memory Management List , "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 21 Oct 2019 at 15:37, Alexander Potapenko wrote: > > On Thu, Oct 17, 2019 at 4:13 PM Marco Elver wrote: > > > > Kernel Concurrency Sanitizer (KCSAN) is a dynamic data-race detector for > > kernel space. KCSAN is a sampling watchpoint-based data-race detector. > > See the included Documentation/dev-tools/kcsan.rst for more details. > > > > This patch adds basic infrastructure, but does not yet enable KCSAN for > > any architecture. > > > > Signed-off-by: Marco Elver > > --- > > v2: > > * Elaborate comment about instrumentation calls emitted by compilers. > > * Replace kcsan_check_access(.., {true, false}) with > > kcsan_check_{read,write} for improved readability. > > * Change bug title of race of unknown origin to just say "data-race in". > > * Refine "Key Properties" in kcsan.rst, and mention observed slow-down. > > * Add comment about safety of find_watchpoint without user_access_save. > > * Remove unnecessary preempt_disable/enable and elaborate on comment why > > we want to disable interrupts and preemptions. > > * Use common struct kcsan_ctx in task_struct and for per-CPU interrupt > > contexts [Suggested by Mark Rutland]. > > --- > > Documentation/dev-tools/kcsan.rst | 203 ++++++++++++++ > > MAINTAINERS | 11 + > > Makefile | 3 +- > > include/linux/compiler-clang.h | 9 + > > include/linux/compiler-gcc.h | 7 + > > include/linux/compiler.h | 35 ++- > > include/linux/kcsan-checks.h | 147 ++++++++++ > > include/linux/kcsan.h | 108 ++++++++ > > include/linux/sched.h | 4 + > > init/init_task.c | 8 + > > init/main.c | 2 + > > kernel/Makefile | 1 + > > kernel/kcsan/Makefile | 14 + > > kernel/kcsan/atomic.c | 21 ++ > > kernel/kcsan/core.c | 428 ++++++++++++++++++++++++++++++ > > kernel/kcsan/debugfs.c | 225 ++++++++++++++++ > > kernel/kcsan/encoding.h | 94 +++++++ > > kernel/kcsan/kcsan.c | 86 ++++++ > > kernel/kcsan/kcsan.h | 140 ++++++++++ > > kernel/kcsan/report.c | 306 +++++++++++++++++++++ > > kernel/kcsan/test.c | 117 ++++++++ > > lib/Kconfig.debug | 2 + > > lib/Kconfig.kcsan | 88 ++++++ > > lib/Makefile | 3 + > > scripts/Makefile.kcsan | 6 + > > scripts/Makefile.lib | 10 + > > 26 files changed, 2069 insertions(+), 9 deletions(-) > > create mode 100644 Documentation/dev-tools/kcsan.rst > > create mode 100644 include/linux/kcsan-checks.h > > create mode 100644 include/linux/kcsan.h > > create mode 100644 kernel/kcsan/Makefile > > create mode 100644 kernel/kcsan/atomic.c > > create mode 100644 kernel/kcsan/core.c > > create mode 100644 kernel/kcsan/debugfs.c > > create mode 100644 kernel/kcsan/encoding.h > > create mode 100644 kernel/kcsan/kcsan.c > > create mode 100644 kernel/kcsan/kcsan.h > > create mode 100644 kernel/kcsan/report.c > > create mode 100644 kernel/kcsan/test.c > > create mode 100644 lib/Kconfig.kcsan > > create mode 100644 scripts/Makefile.kcsan > > > > diff --git a/Documentation/dev-tools/kcsan.rst b/Documentation/dev-tools/kcsan.rst > > new file mode 100644 > > index 000000000000..497b09e5cc96 > > --- /dev/null > > +++ b/Documentation/dev-tools/kcsan.rst > > @@ -0,0 +1,203 @@ > > +The Kernel Concurrency Sanitizer (KCSAN) > > +======================================== > > + > > +Overview > > +-------- > > + > > +*Kernel Concurrency Sanitizer (KCSAN)* is a dynamic data-race detector for > > +kernel space. KCSAN is a sampling watchpoint-based data-race detector -- this > > +is unlike Kernel Thread Sanitizer (KTSAN), which is a happens-before data-race > > +detector. Key priorities in KCSAN's design are lack of false positives, > > +scalability, and simplicity. More details can be found in `Implementation > > +Details`_. > > + > > +KCSAN uses compile-time instrumentation to instrument memory accesses. KCSAN is > > +supported in both GCC and Clang. With GCC it requires version 7.3.0 or later. > > +With Clang it requires version 7.0.0 or later. > > + > > +Usage > > +----- > > + > > +To enable KCSAN configure kernel with:: > > + > > + CONFIG_KCSAN = y > > + > > +KCSAN provides several other configuration options to customize behaviour (see > > +their respective help text for more info). > > + > > +debugfs > > +~~~~~~~ > > + > > +* The file ``/sys/kernel/debug/kcsan`` can be read to get stats. > > + > > +* KCSAN can be turned on or off by writing ``on`` or ``off`` to > > + ``/sys/kernel/debug/kcsan``. > > + > > +* Writing ``!some_func_name`` to ``/sys/kernel/debug/kcsan`` adds > > + ``some_func_name`` to the report filter list, which (by default) blacklists > > + reporting data-races where either one of the top stackframes are a function > > + in the list. > > + > > +* Writing either ``blacklist`` or ``whitelist`` to ``/sys/kernel/debug/kcsan`` > > + changes the report filtering behaviour. For example, the blacklist feature > > + can be used to silence frequently occurring data-races; the whitelist feature > > + can help with reproduction and testing of fixes. > > + > > +Error reports > > +~~~~~~~~~~~~~ > > + > > +A typical data-race report looks like this:: > > + > > + ================================================================== > > + BUG: KCSAN: data-race in generic_permission / kernfs_refresh_inode > > + > > + write to 0xffff8fee4c40700c of 4 bytes by task 175 on cpu 4: > > + kernfs_refresh_inode+0x70/0x170 > > + kernfs_iop_permission+0x4f/0x90 > > + inode_permission+0x190/0x200 > > + link_path_walk.part.0+0x503/0x8e0 > > + path_lookupat.isra.0+0x69/0x4d0 > > + filename_lookup+0x136/0x280 > > + user_path_at_empty+0x47/0x60 > > + vfs_statx+0x9b/0x130 > > + __do_sys_newlstat+0x50/0xb0 > > + __x64_sys_newlstat+0x37/0x50 > > + do_syscall_64+0x85/0x260 > > + entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > + > > + read to 0xffff8fee4c40700c of 4 bytes by task 166 on cpu 6: > > + generic_permission+0x5b/0x2a0 > > + kernfs_iop_permission+0x66/0x90 > > + inode_permission+0x190/0x200 > > + link_path_walk.part.0+0x503/0x8e0 > > + path_lookupat.isra.0+0x69/0x4d0 > > + filename_lookup+0x136/0x280 > > + user_path_at_empty+0x47/0x60 > > + do_faccessat+0x11a/0x390 > > + __x64_sys_access+0x3c/0x50 > > + do_syscall_64+0x85/0x260 > > + entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > + > > + Reported by Kernel Concurrency Sanitizer on: > > + CPU: 6 PID: 166 Comm: systemd-journal Not tainted 5.3.0-rc7+ #1 > > + Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > > + ================================================================== > > + > > +The header of the report provides a short summary of the functions involved in > > +the race. It is followed by the access types and stack traces of the 2 threads > > +involved in the data-race. > > + > > +The other less common type of data-race report looks like this:: > > + > > + ================================================================== > > + BUG: KCSAN: data-race in e1000_clean_rx_irq+0x551/0xb10 > > + > > + race at unknown origin, with read to 0xffff933db8a2ae6c of 1 bytes by interrupt on cpu 0: > > + e1000_clean_rx_irq+0x551/0xb10 > > + e1000_clean+0x533/0xda0 > > + net_rx_action+0x329/0x900 > > + __do_softirq+0xdb/0x2db > > + irq_exit+0x9b/0xa0 > > + do_IRQ+0x9c/0xf0 > > + ret_from_intr+0x0/0x18 > > + default_idle+0x3f/0x220 > > + arch_cpu_idle+0x21/0x30 > > + do_idle+0x1df/0x230 > > + cpu_startup_entry+0x14/0x20 > > + rest_init+0xc5/0xcb > > + arch_call_rest_init+0x13/0x2b > > + start_kernel+0x6db/0x700 > > + > > + Reported by Kernel Concurrency Sanitizer on: > > + CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.3.0-rc7+ #2 > > + Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > > + ================================================================== > > + > > +This report is generated where it was not possible to determine the other > > +racing thread, but a race was inferred due to the data-value of the watched > > +memory location having changed. These can occur either due to missing > > +instrumentation or e.g. DMA accesses. > > + > > +Data-Races > > +---------- > Nit: I was under the impression "data races" were commonly written > without a hyphen. I may be mistaken. Thanks. I've updated it everywhere except in bug titles, which should remain as-is. > > + > > +Informally, two operations *conflict* if they access the same memory location, > > +and at least one of them is a write operation. In an execution, two memory > > +operations from different threads form a **data-race** if they *conflict*, at > > +least one of them is a *plain access* (non-atomic), and they are *unordered* in > > +the "happens-before" order according to the `LKMM > > +<../../tools/memory-model/Documentation/explanation.txt>`_. > > + > > +Relationship with the Linux Kernel Memory Model (LKMM) > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > + > > +The LKMM defines the propagation and ordering rules of various memory > > +operations, which gives developers the ability to reason about concurrent code. > > +Ultimately this allows to determine the possible executions of concurrent code, > > +and if that code is free from data-races. > > + > > +KCSAN is aware of *atomic* accesses (``READ_ONCE``, ``WRITE_ONCE``, > > +``atomic_*``, etc.), but is oblivious of any ordering guarantees. In other > > +words, KCSAN assumes that as long as a plain access is not observed to race > > +with another conflicting access, memory operations are correctly ordered. > > + > > +This means that KCSAN will not report *potential* data-races due to missing > > +memory ordering. If, however, missing memory ordering (that is observable with > > +a particular compiler and architecture) leads to an observable data-race (e.g. > > +entering a critical section erroneously), KCSAN would report the resulting > > +data-race. > > + > > +Implementation Details > > +---------------------- > > + > > +The general approach is inspired by `DataCollider > > +`_. > > +Unlike DataCollider, KCSAN does not use hardware watchpoints, but instead > > +relies on compiler instrumentation. Watchpoints are implemented using an > > +efficient encoding that stores access type, size, and address in a long; the > > +benefits of using "soft watchpoints" are portability and greater flexibility in > > +limiting which accesses trigger a watchpoint. > > + > > +More specifically, KCSAN requires instrumenting plain (unmarked, non-atomic) > > +memory operations; for each instrumented plain access: > > + > > +1. Check if a matching watchpoint exists; if yes, and at least one access is a > > + write, then we encountered a racing access. > > + > > +2. Periodically, if no matching watchpoint exists, set up a watchpoint and > > + stall some delay. > > + > > +3. Also check the data value before the delay, and re-check the data value > > + after delay; if the values mismatch, we infer a race of unknown origin. > > + > > +To detect data-races between plain and atomic memory operations, KCSAN also > > +annotates atomic accesses, but only to check if a watchpoint exists > > +(``kcsan_check_atomic_*``); i.e. KCSAN never sets up a watchpoint on atomic > > +accesses. > > + > > +Key Properties > > +~~~~~~~~~~~~~~ > > + > > +1. **Memory Overhead:** No shadow memory is required. The current > > + implementation uses a small array of longs to encode watchpoint information, > > + which is negligible. > > + > > +2. **Performance Overhead:** KCSAN's runtime aims to be minimal, using an > > + efficient watchpoint encoding that does not require acquiring any shared > > + locks in the fast-path. For kernel boot with a default config on a system > > + where nproc=8 we measure a slow-down of 10-15x. > > + > > +3. **Memory Ordering:** KCSAN is *not* aware of the LKMM's ordering rules. This > > + may result in missed data-races (false negatives), compared to a > > + happens-before data-race detector. > > + > > +4. **Accuracy:** Imprecise, since it uses a sampling strategy. > > + > > +5. **Annotation Overheads:** Minimal annotation is required outside the KCSAN > > + runtime. With a happens-before data-race detector, any omission leads to > > + false positives, which is especially important in the context of the kernel > > + which includes numerous custom synchronization mechanisms. With KCSAN, as a > > + result, maintenance overheads are minimal as the kernel evolves. > > + > > +6. **Detects Racy Writes from Devices:** Due to checking data values upon > > + setting up watchpoints, racy writes from devices can also be detected. > > diff --git a/MAINTAINERS b/MAINTAINERS > > index 0154674cbad3..71f7fb625490 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -8847,6 +8847,17 @@ F: Documentation/kbuild/kconfig* > > F: scripts/kconfig/ > > F: scripts/Kconfig.include > > > > +KCSAN > > +M: Marco Elver > > +R: Dmitry Vyukov > > +L: kasan-dev@googlegroups.com > > +S: Maintained > > +F: Documentation/dev-tools/kcsan.rst > > +F: include/linux/kcsan*.h > > +F: kernel/kcsan/ > > +F: lib/Kconfig.kcsan > > +F: scripts/Makefile.kcsan > > + > > KDUMP > > M: Dave Young > > M: Baoquan He > > diff --git a/Makefile b/Makefile > > index ffd7a912fc46..ad4729176252 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -478,7 +478,7 @@ export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE > > > > export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS > > export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE > > -export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN > > +export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_KCSAN > > export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE > > export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE > > export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL > > @@ -900,6 +900,7 @@ endif > > include scripts/Makefile.kasan > > include scripts/Makefile.extrawarn > > include scripts/Makefile.ubsan > > +include scripts/Makefile.kcsan > > > > # Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments > > KBUILD_CPPFLAGS += $(KCPPFLAGS) > > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h > > index 333a6695a918..a213eb55e725 100644 > > --- a/include/linux/compiler-clang.h > > +++ b/include/linux/compiler-clang.h > > @@ -24,6 +24,15 @@ > > #define __no_sanitize_address > > #endif > > > > +#if __has_feature(thread_sanitizer) > > +/* emulate gcc's __SANITIZE_THREAD__ flag */ > > +#define __SANITIZE_THREAD__ > > +#define __no_sanitize_thread \ > > + __attribute__((no_sanitize("thread"))) > > +#else > > +#define __no_sanitize_thread > > +#endif > > + > > /* > > * Not all versions of clang implement the the type-generic versions > > * of the builtin overflow checkers. Fortunately, clang implements > > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h > > index d7ee4c6bad48..de105ca29282 100644 > > --- a/include/linux/compiler-gcc.h > > +++ b/include/linux/compiler-gcc.h > > @@ -145,6 +145,13 @@ > > #define __no_sanitize_address > > #endif > > > > +#if __has_attribute(__no_sanitize_thread__) && defined(__SANITIZE_THREAD__) > > +#define __no_sanitize_thread \ > > + __attribute__((__noinline__)) __attribute__((no_sanitize_thread)) > > +#else > > +#define __no_sanitize_thread > > +#endif > > + > > #if GCC_VERSION >= 50100 > > #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 > > #endif > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > index 5e88e7e33abe..350d80dbee4d 100644 > > --- a/include/linux/compiler.h > > +++ b/include/linux/compiler.h > > @@ -178,6 +178,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, > > #endif > > > > #include > > +#include > > > > #define __READ_ONCE_SIZE \ > > ({ \ > > @@ -193,12 +194,6 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, > > } \ > > }) > > > > -static __always_inline > > -void __read_once_size(const volatile void *p, void *res, int size) > > -{ > > - __READ_ONCE_SIZE; > > -} > > - > > #ifdef CONFIG_KASAN > > /* > > * We can't declare function 'inline' because __no_sanitize_address confilcts > > @@ -211,14 +206,38 @@ void __read_once_size(const volatile void *p, void *res, int size) > > # define __no_kasan_or_inline __always_inline > > #endif > > > > -static __no_kasan_or_inline > > +#ifdef CONFIG_KCSAN > > +# define __no_kcsan_or_inline __no_sanitize_thread notrace __maybe_unused > > +#else > > +# define __no_kcsan_or_inline __always_inline > > +#endif > > + > > +#if defined(CONFIG_KASAN) || defined(CONFIG_KCSAN) > > +/* Avoid any instrumentation or inline. */ > > +#define __no_sanitize_or_inline \ > > + __no_sanitize_address __no_sanitize_thread notrace __maybe_unused > > +#else > > +#define __no_sanitize_or_inline __always_inline > > +#endif > > + > > +static __no_kcsan_or_inline > > +void __read_once_size(const volatile void *p, void *res, int size) > > +{ > > + kcsan_check_atomic_read((const void *)p, size); > > + __READ_ONCE_SIZE; > > +} > > + > > +static __no_sanitize_or_inline > > void __read_once_size_nocheck(const volatile void *p, void *res, int size) > > { > > __READ_ONCE_SIZE; > > } > > > > -static __always_inline void __write_once_size(volatile void *p, void *res, int size) > > +static __no_kcsan_or_inline > > +void __write_once_size(volatile void *p, void *res, int size) > > { > > + kcsan_check_atomic_write((const void *)p, size); > > + > > switch (size) { > > case 1: *(volatile __u8 *)p = *(__u8 *)res; break; > > case 2: *(volatile __u16 *)p = *(__u16 *)res; break; > > diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h > > new file mode 100644 > > index 000000000000..4203603ae852 > > --- /dev/null > > +++ b/include/linux/kcsan-checks.h > > @@ -0,0 +1,147 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > + > > +#ifndef _LINUX_KCSAN_CHECKS_H > > +#define _LINUX_KCSAN_CHECKS_H > > + > > +#include > > + > > +/* > > + * __kcsan_*: Always available when KCSAN is enabled. This may be used > > + * even in compilation units that selectively disable KCSAN, but must use KCSAN > > + * to validate access to an address. Never use these in header files! > > + */ > > +#ifdef CONFIG_KCSAN > > +/** > > + * __kcsan_check_watchpoint - check if a watchpoint exists > > + * > > + * Returns true if no race was detected, and we may then proceed to set up a > > + * watchpoint after. Returns false if either KCSAN is disabled or a race was > > + * encountered, and we may not set up a watchpoint after. > > + * > > + * @ptr address of access > > + * @size size of access > > + * @is_write is access a write > > + * @return true if no race was detected, false otherwise. > > + */ > > +bool __kcsan_check_watchpoint(const volatile void *ptr, size_t size, > > + bool is_write); > I think the parameter indentations are a bit off here and below (I've > also looked at the Github diff); > have you considered running checkpatch.pl? It was formatted with clang-format, it's correct with 8 space tabs. checkpath.pl is happy. > > + > > +/** > > + * __kcsan_setup_watchpoint - set up watchpoint and report data-races > > + * > > + * Sets up a watchpoint (if sampled), and if a racing access was observed, > > + * reports the data-race. > > + * > > + * @ptr address of access > > + * @size size of access > > + * @is_write is access a write > > + */ > > +void __kcsan_setup_watchpoint(const volatile void *ptr, size_t size, > > + bool is_write); > > +#else > > +static inline bool __kcsan_check_watchpoint(const volatile void *ptr, > > + size_t size, bool is_write) > > +{ > > + return true; > > +} > > +static inline void __kcsan_setup_watchpoint(const volatile void *ptr, > > + size_t size, bool is_write) > > +{ > > +} > > +#endif > > + > > +/* > > + * kcsan_*: Only available when the particular compilation unit has KCSAN > > + * instrumentation enabled. May be used in header files. > > + */ > > +#ifdef __SANITIZE_THREAD__ > > +#define kcsan_check_watchpoint __kcsan_check_watchpoint > > +#define kcsan_setup_watchpoint __kcsan_setup_watchpoint > > +#else > > +static inline bool kcsan_check_watchpoint(const volatile void *ptr, size_t size, > > + bool is_write) > > +{ > > + return true; > > +} > > +static inline void kcsan_setup_watchpoint(const volatile void *ptr, size_t size, > > + bool is_write) > > +{ > > +} > > +#endif > > + > > +/** > > + * __kcsan_check_read - check regular read access for data-races > > + * > > + * Full read access that checks watchpoint and sets up a watchpoint if this > > + * access is sampled. Note that, setting up watchpoints for plain reads is > > + * required to also detect data-races with atomic accesses. > > + * > > + * @ptr address of access > > + * @size size of access > > + */ > > +#define __kcsan_check_read(ptr, size) \ > > + do { \ > > + if (__kcsan_check_watchpoint(ptr, size, false)) \ > > + __kcsan_setup_watchpoint(ptr, size, false); \ > > + } while (0) > > + > > +/** > > + * __kcsan_check_write - check regular write access for data-races > > + * > > + * Full write access that checks watchpoint and sets up a watchpoint if this > > + * access is sampled. > > + * > > + * @ptr address of access > > + * @size size of access > > + */ > > +#define __kcsan_check_write(ptr, size) \ > > + do { \ > > + if (__kcsan_check_watchpoint(ptr, size, true) && \ > > + !IS_ENABLED(CONFIG_KCSAN_PLAIN_WRITE_PRETEND_ONCE)) \ > > + __kcsan_setup_watchpoint(ptr, size, true); \ > > + } while (0) > > + > > +/** > > + * kcsan_check_read - check regular read access for data-races > > + * > > + * @ptr address of access > > + * @size size of access > > + */ > > +#define kcsan_check_read(ptr, size) \ > > + do { \ > > + if (kcsan_check_watchpoint(ptr, size, false)) \ > > + kcsan_setup_watchpoint(ptr, size, false); \ > > + } while (0) > > + > > +/** > > + * kcsan_check_write - check regular write access for data-races > > + * > > + * @ptr address of access > > + * @size size of access > > + */ > > +#define kcsan_check_write(ptr, size) \ > > + do { \ > > + if (kcsan_check_watchpoint(ptr, size, true) && \ > > + !IS_ENABLED(CONFIG_KCSAN_PLAIN_WRITE_PRETEND_ONCE)) \ > > + kcsan_setup_watchpoint(ptr, size, true); \ > > + } while (0) > > + > > +/* > > + * Check for atomic accesses: if atomic access are not ignored, this simply > > + * aliases to kcsan_check_watchpoint, otherwise becomes a no-op. > > + */ > > +#ifdef CONFIG_KCSAN_IGNORE_ATOMICS > > +#define kcsan_check_atomic_read(...) \ > > + do { \ > > + } while (0) > > +#define kcsan_check_atomic_write(...) \ > > + do { \ > > + } while (0) > > +#else > > +#define kcsan_check_atomic_read(ptr, size) \ > > + kcsan_check_watchpoint(ptr, size, false) > > +#define kcsan_check_atomic_write(ptr, size) \ > > + kcsan_check_watchpoint(ptr, size, true) > > +#endif > > + > > +#endif /* _LINUX_KCSAN_CHECKS_H */ > > diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h > > new file mode 100644 > > index 000000000000..fd5de2ba3a16 > > --- /dev/null > > +++ b/include/linux/kcsan.h > > @@ -0,0 +1,108 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > + > > +#ifndef _LINUX_KCSAN_H > > +#define _LINUX_KCSAN_H > > + > > +#include > > +#include > > + > > +#ifdef CONFIG_KCSAN > > + > > +/* > > + * Context for each thread of execution: for tasks, this is stored in > > + * task_struct, and interrupts access internal per-CPU storage. > > + */ > > +struct kcsan_ctx { > > + int disable; /* disable counter */ > > + int atomic_next; /* number of following atomic ops */ > > + > > + /* > > + * We use separate variables to store if we are in a nestable or flat > > + * atomic region. This helps make sure that an atomic region with > > + * nesting support is not suddenly aborted when a flat region is > > + * contained within. Effectively this allows supporting nesting flat > > + * atomic regions within an outer nestable atomic region. Support for > > + * this is required as there are cases where a seqlock reader critical > > + * section (flat atomic region) is contained within a seqlock writer > > + * critical section (nestable atomic region), and the "mismatching > > + * kcsan_end_atomic()" warning would trigger otherwise. > > + */ > > + int atomic_region; > > + bool atomic_region_flat; > > +}; > > + > > +/** > > + * kcsan_init - initialize KCSAN runtime > > + */ > > +void kcsan_init(void); > > + > > +/** > > + * kcsan_disable_current - disable KCSAN for the current context > > + * > > + * Supports nesting. > > + */ > > +void kcsan_disable_current(void); > > + > > +/** > > + * kcsan_enable_current - re-enable KCSAN for the current context > > + * > > + * Supports nesting. > > + */ > > +void kcsan_enable_current(void); > > + > > +/** > > + * kcsan_begin_atomic - use to denote an atomic region > > + * > > + * Accesses within the atomic region may appear to race with other accesses but > > + * should be considered atomic. > > + * > > + * @nest true if regions may be nested, or false for flat region > > + */ > > +void kcsan_begin_atomic(bool nest); > > + > > +/** > > + * kcsan_end_atomic - end atomic region > > + * > > + * @nest must match argument to kcsan_begin_atomic(). > > + */ > > +void kcsan_end_atomic(bool nest); > > + > > +/** > > + * kcsan_atomic_next - consider following accesses as atomic > > + * > > + * Force treating the next n memory accesses for the current context as atomic > > + * operations. > > + * > > + * @n number of following memory accesses to treat as atomic. > > + */ > > +void kcsan_atomic_next(int n); > > + > > +#else /* CONFIG_KCSAN */ > > + > > +static inline void kcsan_init(void) > I think it should be ok to put {} on the same line with the function > prototype here, see e.g. include/linux/kasan.h Done @ v3. > > +{ > > +} > > + > > +static inline void kcsan_disable_current(void) > > +{ > > +} > > + > > +static inline void kcsan_enable_current(void) > > +{ > > +} > > + > > +static inline void kcsan_begin_atomic(bool nest) > > +{ > > +} > > + > > +static inline void kcsan_end_atomic(bool nest) > > +{ > > +} > > + > > +static inline void kcsan_atomic_next(int n) > > +{ > > +} > > + > > +#endif /* CONFIG_KCSAN */ > > + > > +#endif /* _LINUX_KCSAN_H */ > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index 2c2e56bd8913..9490e417bf4a 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -31,6 +31,7 @@ > > #include > > #include > > #include > > +#include > > > > /* task_struct member predeclarations (sorted alphabetically): */ > > struct audit_context; > > @@ -1171,6 +1172,9 @@ struct task_struct { > > #ifdef CONFIG_KASAN > > unsigned int kasan_depth; > > #endif > > +#ifdef CONFIG_KCSAN > > + struct kcsan_ctx kcsan_ctx; > > +#endif > > > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > > /* Index of current stored address in ret_stack: */ > > diff --git a/init/init_task.c b/init/init_task.c > > index 9e5cbe5eab7b..e229416c3314 100644 > > --- a/init/init_task.c > > +++ b/init/init_task.c > > @@ -161,6 +161,14 @@ struct task_struct init_task > > #ifdef CONFIG_KASAN > > .kasan_depth = 1, > > #endif > > +#ifdef CONFIG_KCSAN > > + .kcsan_ctx = { > > + .disable = 1, > > + .atomic_next = 0, > > + .atomic_region = 0, > > + .atomic_region_flat = 0, > > + }, > > +#endif > > #ifdef CONFIG_TRACE_IRQFLAGS > > .softirqs_enabled = 1, > > #endif > > diff --git a/init/main.c b/init/main.c > > index 91f6ebb30ef0..4d814de017ee 100644 > > --- a/init/main.c > > +++ b/init/main.c > > @@ -93,6 +93,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -779,6 +780,7 @@ asmlinkage __visible void __init start_kernel(void) > > acpi_subsystem_init(); > > arch_post_acpi_subsys_init(); > > sfi_init_late(); > > + kcsan_init(); > > > > /* Do the rest non-__init'ed, we're now alive */ > > arch_call_rest_init(); > > diff --git a/kernel/Makefile b/kernel/Makefile > > index daad787fb795..74ab46e2ebd1 100644 > > --- a/kernel/Makefile > > +++ b/kernel/Makefile > > @@ -102,6 +102,7 @@ obj-$(CONFIG_TRACEPOINTS) += trace/ > > obj-$(CONFIG_IRQ_WORK) += irq_work.o > > obj-$(CONFIG_CPU_PM) += cpu_pm.o > > obj-$(CONFIG_BPF) += bpf/ > > +obj-$(CONFIG_KCSAN) += kcsan/ > > > > obj-$(CONFIG_PERF_EVENTS) += events/ > > > > diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile > > new file mode 100644 > > index 000000000000..c25f07062d26 > > --- /dev/null > > +++ b/kernel/kcsan/Makefile > > @@ -0,0 +1,14 @@ > > +# SPDX-License-Identifier: GPL-2.0 > > +KCSAN_SANITIZE := n > > +KCOV_INSTRUMENT := n > > + > > +CFLAGS_REMOVE_kcsan.o = $(CC_FLAGS_FTRACE) > > +CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE) > > +CFLAGS_REMOVE_atomic.o = $(CC_FLAGS_FTRACE) > > + > > +CFLAGS_kcsan.o = $(call cc-option, -fno-conserve-stack -fno-stack-protector) > > +CFLAGS_core.o = $(call cc-option, -fno-conserve-stack -fno-stack-protector) > > +CFLAGS_atomic.o = $(call cc-option, -fno-conserve-stack -fno-stack-protector) > > + > > +obj-y := kcsan.o core.o atomic.o debugfs.o report.o > > +obj-$(CONFIG_KCSAN_SELFTEST) += test.o > > diff --git a/kernel/kcsan/atomic.c b/kernel/kcsan/atomic.c > > new file mode 100644 > > index 000000000000..dd44f7d9e491 > > --- /dev/null > > +++ b/kernel/kcsan/atomic.c > > @@ -0,0 +1,21 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +#include > > + > > +#include "kcsan.h" > > + > > +/* > > + * List all volatile globals that have been observed in races, to suppress > > + * data-race reports between accesses to these variables. > > + * > > + * For now, we assume that volatile accesses of globals are as strong as atomic > > + * accesses (READ_ONCE, WRITE_ONCE cast to volatile). The situation is still not > > + * entirely clear, as on some architectures (Alpha) READ_ONCE/WRITE_ONCE do more > > + * than cast to volatile. Eventually, we hope to be able to remove this > > + * function. > > + */ > > +bool kcsan_is_atomic(const volatile void *ptr) > > +{ > > + /* only jiffies for now */ > > + return ptr == &jiffies; > > +} > > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c > > new file mode 100644 > > index 000000000000..bc8d60b129eb > > --- /dev/null > > +++ b/kernel/kcsan/core.c > > @@ -0,0 +1,428 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#include "kcsan.h" > > +#include "encoding.h" > > + > > +/* > > + * Helper macros to iterate slots, starting from address slot itself, followed > > + * by the right and left slots. > > + */ > > +#define CHECK_NUM_SLOTS (1 + 2 * KCSAN_CHECK_ADJACENT) > > +#define SLOT_IDX(slot, i) \ > > + ((slot + (((i + KCSAN_CHECK_ADJACENT) % CHECK_NUM_SLOTS) - \ > > + KCSAN_CHECK_ADJACENT)) % \ > > + KCSAN_NUM_WATCHPOINTS) > > + > > +bool kcsan_enabled; > > + > > +/* Per-CPU kcsan_ctx for interrupts */ > > +static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = { > > + .disable = 0, > > + .atomic_next = 0, > > + .atomic_region = 0, > > + .atomic_region_flat = 0, > > +}; > > + > > +/* > > + * Watchpoints, with each entry encoded as defined in encoding.h: in order to be > > + * able to safely update and access a watchpoint without introducing locking > > + * overhead, we encode each watchpoint as a single atomic long. The initial > > + * zero-initialized state matches INVALID_WATCHPOINT. > > + */ > > +static atomic_long_t watchpoints[KCSAN_NUM_WATCHPOINTS]; > > + > > +/* > > + * Instructions skipped counter; see should_watch(). > > + */ > > +static DEFINE_PER_CPU(unsigned long, kcsan_skip); > > + > > +static inline atomic_long_t *find_watchpoint(unsigned long addr, size_t size, > > + bool expect_write, > > + long *encoded_watchpoint) > > +{ > > + const int slot = watchpoint_slot(addr); > > + const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK; > > + atomic_long_t *watchpoint; > > + unsigned long wp_addr_masked; > > + size_t wp_size; > > + bool is_write; > > + int i; > > + > > + for (i = 0; i < CHECK_NUM_SLOTS; ++i) { > > + watchpoint = &watchpoints[SLOT_IDX(slot, i)]; > > + *encoded_watchpoint = atomic_long_read(watchpoint); > > + if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked, > > + &wp_size, &is_write)) > > + continue; > > + > > + if (expect_write && !is_write) > > + continue; > > + > > + /* Check if the watchpoint matches the access. */ > > + if (matching_access(wp_addr_masked, wp_size, addr_masked, size)) > > + return watchpoint; > > + } > > + > > + return NULL; > > +} > > + > > +static inline atomic_long_t *insert_watchpoint(unsigned long addr, size_t size, > > + bool is_write) > > +{ > > + const int slot = watchpoint_slot(addr); > > + const long encoded_watchpoint = encode_watchpoint(addr, size, is_write); > > + atomic_long_t *watchpoint; > > + int i; > > + > > + for (i = 0; i < CHECK_NUM_SLOTS; ++i) { > > + long expect_val = INVALID_WATCHPOINT; > > + > > + /* Try to acquire this slot. */ > > + watchpoint = &watchpoints[SLOT_IDX(slot, i)]; > > + if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, > > + encoded_watchpoint)) > > + return watchpoint; > > + } > > + > > + return NULL; > > +} > > + > > +/* > > + * Return true if watchpoint was successfully consumed, false otherwise. > > + * > > + * This may return false if: > > + * > > + * 1. another thread already consumed the watchpoint; > > + * 2. the thread that set up the watchpoint already removed it; > > + * 3. the watchpoint was removed and then re-used. > > + */ > > +static inline bool try_consume_watchpoint(atomic_long_t *watchpoint, > > + long encoded_watchpoint) > > +{ > > + return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, > > + CONSUMED_WATCHPOINT); > > +} > > + > > +/* > > + * Return true if watchpoint was not touched, false if consumed. > > + */ > > +static inline bool remove_watchpoint(atomic_long_t *watchpoint) > > +{ > > + return atomic_long_xchg_relaxed(watchpoint, INVALID_WATCHPOINT) != > > + CONSUMED_WATCHPOINT; > > +} > > + > > +static inline struct kcsan_ctx *get_ctx(void) > > +{ > > + /* > > + * In interrupt, use raw_cpu_ptr to avoid unnecessary checks, that would > > + * also result in calls that generate warnings in uaccess regions. > > + */ > > + return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx); > > +} > > + > > + > > +static inline bool is_atomic(const volatile void *ptr) > > +{ > > + struct kcsan_ctx *ctx = get_ctx(); > > + > > + if (unlikely(ctx->atomic_next > 0)) { > > + --ctx->atomic_next; > > + return true; > > + } > > + if (unlikely(ctx->atomic_region > 0 || ctx->atomic_region_flat)) > > + return true; > Won't ctx->atomic_region suffice for both flat and non-flat regions? > (Do we really need the flat ones?) The comment in include/linux/kcsan.h explains: /* * We use separate variables to store if we are in a nestable or flat * atomic region. This helps make sure that an atomic region with * nesting support is not suddenly aborted when a flat region is * contained within. Effectively this allows supporting nesting flat * atomic regions within an outer nestable atomic region. Support for * this is required as there are cases where a seqlock reader critical * section (flat atomic region) is contained within a seqlock writer * critical section (nestable atomic region), and the "mismatching * kcsan_end_atomic()" warning would trigger otherwise. */ > > + return kcsan_is_atomic(ptr); > > +} > > + > > +static inline bool should_watch(const volatile void *ptr) > > +{ > > + /* > > + * Never set up watchpoints when memory operations are atomic. > > + * > > + * We need to check this first, because: 1) atomics should not count > > + * towards skipped instructions below, and 2) to actually decrement > > + * kcsan_atomic_next for each atomic. > > + */ > > + if (is_atomic(ptr)) > > + return false; > > + > > + /* > > + * We use a per-CPU counter, to avoid excessive contention; there is > > + * still enough non-determinism for the precise instructions that end up > > + * being watched to be mostly unpredictable. Using a PRNG like > > + * prandom_u32() turned out to be too slow. > > + */ > > + return (this_cpu_inc_return(kcsan_skip) % > > + CONFIG_KCSAN_WATCH_SKIP_INST) == 0; > > +} > > + > > +static inline bool is_enabled(void) > > +{ > > + return READ_ONCE(kcsan_enabled) && get_ctx()->disable == 0; > > +} > > + > > +static inline unsigned int get_delay(void) > > +{ > > + unsigned int max_delay = in_task() ? CONFIG_KCSAN_UDELAY_MAX_TASK : > > + CONFIG_KCSAN_UDELAY_MAX_INTERRUPT; > > + return IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ? > > + ((prandom_u32() % max_delay) + 1) : > > + max_delay; > > +} > > + > > +/* === Public interface ===================================================== */ > > + > > +void __init kcsan_init(void) > > +{ > > + BUG_ON(!in_task()); > > + > > + kcsan_debugfs_init(); > > + kcsan_enable_current(); > > +#ifdef CONFIG_KCSAN_EARLY_ENABLE > > + /* > > + * We are in the init task, and no other tasks should be running. > > + */ > > + WRITE_ONCE(kcsan_enabled, true); > > +#endif > > +} > > + > > +/* === Exported interface =================================================== */ > > + > > +void kcsan_disable_current(void) > > +{ > > + ++get_ctx()->disable; > > +} > > +EXPORT_SYMBOL(kcsan_disable_current); > > + > > +void kcsan_enable_current(void) > > +{ > > + if (get_ctx()->disable-- == 0) { > > + kcsan_disable_current(); /* restore to 0 */ > > + kcsan_disable_current(); > > + WARN(1, "mismatching %s", __func__); > > + kcsan_enable_current(); > > + } > > +} > > +EXPORT_SYMBOL(kcsan_enable_current); > > + > > +void kcsan_begin_atomic(bool nest) > > +{ > > + if (nest) > > + ++get_ctx()->atomic_region; > > + else > > + get_ctx()->atomic_region_flat = true; > > +} > > +EXPORT_SYMBOL(kcsan_begin_atomic); > > + > > +void kcsan_end_atomic(bool nest) > > +{ > > + if (nest) { > > + if (get_ctx()->atomic_region-- == 0) { > > + kcsan_begin_atomic(true); /* restore to 0 */ > > + kcsan_disable_current(); > > + WARN(1, "mismatching %s", __func__); > > + kcsan_enable_current(); > > + } > > + } else { > > + get_ctx()->atomic_region_flat = false; > > + } > > +} > > +EXPORT_SYMBOL(kcsan_end_atomic); > > + > > +void kcsan_atomic_next(int n) > > +{ > > + get_ctx()->atomic_next = n; > > +} > > +EXPORT_SYMBOL(kcsan_atomic_next); > > + > > +bool __kcsan_check_watchpoint(const volatile void *ptr, size_t size, > > + bool is_write) > > +{ > > + atomic_long_t *watchpoint; > > + long encoded_watchpoint; > > + unsigned long flags; > > + enum kcsan_report_type report_type; > > + > > + if (unlikely(!is_enabled())) > > + return false; > > + > > + /* > > + * Avoid user_access_save in fast-path here: find_watchpoint is safe > > + * without user_access_save, as the address that ptr points to is only > > + * used to check if a watchpoint exists; ptr is never dereferenced. > > + */ > > + watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write, > > + &encoded_watchpoint); > > + if (watchpoint == NULL) > > + return true; > > + > > + flags = user_access_save(); > > + if (!try_consume_watchpoint(watchpoint, encoded_watchpoint)) { > > + /* > > + * The other thread may not print any diagnostics, as it has > > + * already removed the watchpoint, or another thread consumed > > + * the watchpoint before this thread. > > + */ > > + kcsan_counter_inc(kcsan_counter_report_races); > > + report_type = kcsan_report_race_check_race; > > + } else { > > + report_type = kcsan_report_race_check; > > + } > > + > > + /* Encountered a data-race. */ > > + kcsan_counter_inc(kcsan_counter_data_races); > > + kcsan_report(ptr, size, is_write, raw_smp_processor_id(), report_type); > > + > > + user_access_restore(flags); > > + return false; > > +} > > +EXPORT_SYMBOL(__kcsan_check_watchpoint); > > + > > +void __kcsan_setup_watchpoint(const volatile void *ptr, size_t size, > > + bool is_write) > > +{ > > + atomic_long_t *watchpoint; > > + union { > > + u8 _1; > > + u16 _2; > > + u32 _4; > > + u64 _8; > > + } expect_value; > > + bool is_expected = true; > > + unsigned long ua_flags = user_access_save(); > > + unsigned long irq_flags; > > + > > + if (!should_watch(ptr)) > > + goto out; > > + > > + if (!check_encodable((unsigned long)ptr, size)) { > > + kcsan_counter_inc(kcsan_counter_unencodable_accesses); > > + goto out; > > + } > > + > > + /* > > + * Disable interrupts & preemptions to avoid another thread on the same > > + * CPU accessing memory locations for the set up watchpoint; this is to > > + * avoid reporting races to e.g. CPU-local data. > > + * > > + * An alternative would be adding the source CPU to the watchpoint > > + * encoding, and checking that watchpoint-CPU != this-CPU. There are > > + * several problems with this: > > + * 1. we should avoid stealing more bits from the watchpoint encoding > > + * as it would affect accuracy, as well as increase performance > > + * overhead in the fast-path; > > + * 2. if we are preempted, but there *is* a genuine data-race, we > > + * would *not* report it -- since this is the common case (vs. > > + * CPU-local data accesses), it makes more sense (from a data-race > > + * detection PoV) to simply disable preemptions to ensure as many > > + * tasks as possible run on other CPUs. > > + */ > > + local_irq_save(irq_flags); > > + > > + watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); > > + if (watchpoint == NULL) { > > + /* > > + * Out of capacity: the size of `watchpoints`, and the frequency > > + * with which `should_watch()` returns true should be tweaked so > > + * that this case happens very rarely. > > + */ > > + kcsan_counter_inc(kcsan_counter_no_capacity); > > + goto out_unlock; > > + } > > + > > + kcsan_counter_inc(kcsan_counter_setup_watchpoints); > > + kcsan_counter_inc(kcsan_counter_used_watchpoints); > > + > > + /* > > + * Read the current value, to later check and infer a race if the data > > + * was modified via a non-instrumented access, e.g. from a device. > > + */ > > + switch (size) { > > + case 1: > > + expect_value._1 = READ_ONCE(*(const u8 *)ptr); > > + break; > > + case 2: > > + expect_value._2 = READ_ONCE(*(const u16 *)ptr); > > + break; > > + case 4: > > + expect_value._4 = READ_ONCE(*(const u32 *)ptr); > > + break; > > + case 8: > > + expect_value._8 = READ_ONCE(*(const u64 *)ptr); > > + break; > > + default: > > + break; /* ignore; we do not diff the values */ > > + } > > + > > +#ifdef CONFIG_KCSAN_DEBUG > > + kcsan_disable_current(); > > + pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n", > > + is_write ? "write" : "read", size, ptr, > > + watchpoint_slot((unsigned long)ptr), > > + encode_watchpoint((unsigned long)ptr, size, is_write)); > > + kcsan_enable_current(); > > +#endif > > + > > + /* > > + * Delay this thread, to increase probability of observing a racy > > + * conflicting access. > > + */ > > + udelay(get_delay()); > > + > > + /* > > + * Re-read value, and check if it is as expected; if not, we infer a > > + * racy access. > > + */ > > + switch (size) { > > + case 1: > > + is_expected = expect_value._1 == READ_ONCE(*(const u8 *)ptr); > > + break; > > + case 2: > > + is_expected = expect_value._2 == READ_ONCE(*(const u16 *)ptr); > > + break; > > + case 4: > > + is_expected = expect_value._4 == READ_ONCE(*(const u32 *)ptr); > > + break; > > + case 8: > > + is_expected = expect_value._8 == READ_ONCE(*(const u64 *)ptr); > > + break; > > + default: > > + break; /* ignore; we do not diff the values */ > > + } > > + > > + /* Check if this access raced with another. */ > > + if (!remove_watchpoint(watchpoint)) { > > + /* > > + * No need to increment 'race' counter, as the racing thread > > + * already did. > > + */ > > + kcsan_report(ptr, size, is_write, smp_processor_id(), > > + kcsan_report_race_setup); > > + } else if (!is_expected) { > > + /* Inferring a race, since the value should not have changed. */ > > + kcsan_counter_inc(kcsan_counter_races_unknown_origin); > > +#ifdef CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN > > + kcsan_report(ptr, size, is_write, smp_processor_id(), > > + kcsan_report_race_unknown_origin); > > +#endif > > + } > > + > > + kcsan_counter_dec(kcsan_counter_used_watchpoints); > > +out_unlock: > > + local_irq_restore(irq_flags); > > +out: > > + user_access_restore(ua_flags); > > +} > > +EXPORT_SYMBOL(__kcsan_setup_watchpoint); > > diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c > > new file mode 100644 > > index 000000000000..6ddcbd185f3a > > --- /dev/null > > +++ b/kernel/kcsan/debugfs.c > > @@ -0,0 +1,225 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#include "kcsan.h" > > + > > +/* > > + * Statistics counters. > > + */ > > +static atomic_long_t counters[kcsan_counter_count]; > > + > > +/* > > + * Addresses for filtering functions from reporting. This list can be used as a > > + * whitelist or blacklist. > > + */ > > +static struct { > > + unsigned long *addrs; /* array of addresses */ > > + size_t size; /* current size */ > > + int used; /* number of elements used */ > > + bool sorted; /* if elements are sorted */ > > + bool whitelist; /* if list is a blacklist or whitelist */ > > +} report_filterlist = { > > + .addrs = NULL, > > + .size = 8, /* small initial size */ > > + .used = 0, > > + .sorted = false, > > + .whitelist = false, /* default is blacklist */ > > +}; > > +static DEFINE_SPINLOCK(report_filterlist_lock); > > + > > +static const char *counter_to_name(enum kcsan_counter_id id) > > +{ > > + switch (id) { > > + case kcsan_counter_used_watchpoints: > > + return "used_watchpoints"; > > + case kcsan_counter_setup_watchpoints: > > + return "setup_watchpoints"; > > + case kcsan_counter_data_races: > > + return "data_races"; > > + case kcsan_counter_no_capacity: > > + return "no_capacity"; > > + case kcsan_counter_report_races: > > + return "report_races"; > > + case kcsan_counter_races_unknown_origin: > > + return "races_unknown_origin"; > > + case kcsan_counter_unencodable_accesses: > > + return "unencodable_accesses"; > > + case kcsan_counter_encoding_false_positives: > > + return "encoding_false_positives"; > > + case kcsan_counter_count: > > + BUG(); > > + } > > + return NULL; > > +} > > + > > +void kcsan_counter_inc(enum kcsan_counter_id id) > > +{ > > + atomic_long_inc(&counters[id]); > > +} > > + > > +void kcsan_counter_dec(enum kcsan_counter_id id) > > +{ > > + atomic_long_dec(&counters[id]); > > +} > > + > > +static int cmp_filterlist_addrs(const void *rhs, const void *lhs) > > +{ > > + const unsigned long a = *(const unsigned long *)rhs; > > + const unsigned long b = *(const unsigned long *)lhs; > > + > > + return a < b ? -1 : a == b ? 0 : 1; > > +} > > + > > +bool kcsan_skip_report(unsigned long func_addr) > > +{ > > + unsigned long symbolsize, offset; > > + unsigned long flags; > > + bool ret = false; > > + > > + if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset)) > > + return false; > > + func_addr -= offset; /* get function start */ > > + > > + spin_lock_irqsave(&report_filterlist_lock, flags); > > + if (report_filterlist.used == 0) > > + goto out; > > + > > + /* Sort array if it is unsorted, and then do a binary search. */ > > + if (!report_filterlist.sorted) { > > + sort(report_filterlist.addrs, report_filterlist.used, > > + sizeof(unsigned long), cmp_filterlist_addrs, NULL); > > + report_filterlist.sorted = true; > > + } > > + ret = !!bsearch(&func_addr, report_filterlist.addrs, > > + report_filterlist.used, sizeof(unsigned long), > > + cmp_filterlist_addrs); > > + if (report_filterlist.whitelist) > > + ret = !ret; > > + > > +out: > > + spin_unlock_irqrestore(&report_filterlist_lock, flags); > > + return ret; > > +} > > + > > +static void set_report_filterlist_whitelist(bool whitelist) > > +{ > > + unsigned long flags; > > + > > + spin_lock_irqsave(&report_filterlist_lock, flags); > > + report_filterlist.whitelist = whitelist; > > + spin_unlock_irqrestore(&report_filterlist_lock, flags); > > +} > > + > > +static void insert_report_filterlist(const char *func) > > +{ > > + unsigned long flags; > > + unsigned long addr = kallsyms_lookup_name(func); > > + > > + if (!addr) { > > + pr_err("KCSAN: could not find function: '%s'\n", func); > > + return; > > + } > > + > > + spin_lock_irqsave(&report_filterlist_lock, flags); > > + > > + if (report_filterlist.addrs == NULL) > > + report_filterlist.addrs = /* initial allocation */ > > + kvmalloc_array(report_filterlist.size, > > + sizeof(unsigned long), GFP_KERNEL); > You need to use braces in both branches here: > https://www.kernel.org/doc/html/v4.10/process/coding-style.html#placing-braces-and-spaces Done @ v3. > > + else if (report_filterlist.used == report_filterlist.size) { > > + /* resize filterlist */ > > + unsigned long *new_addrs; > > + > > + report_filterlist.size *= 2; > > + new_addrs = kvmalloc_array(report_filterlist.size, > > + sizeof(unsigned long), GFP_KERNEL); > > + memcpy(new_addrs, report_filterlist.addrs, > > + report_filterlist.used * sizeof(unsigned long)); > > + kvfree(report_filterlist.addrs); > > + report_filterlist.addrs = new_addrs; > > + } > > + > > + /* Note: deduplicating should be done in userspace. */ > > + report_filterlist.addrs[report_filterlist.used++] = > > + kallsyms_lookup_name(func); > > + report_filterlist.sorted = false; > > + > > + spin_unlock_irqrestore(&report_filterlist_lock, flags); > > +} > > + > > +static int show_info(struct seq_file *file, void *v) > > +{ > > + int i; > > + unsigned long flags; > > + > > + /* show stats */ > > + seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled)); > > + for (i = 0; i < kcsan_counter_count; ++i) > > + seq_printf(file, "%s: %ld\n", counter_to_name(i), > > + atomic_long_read(&counters[i])); > > + > > + /* show filter functions, and filter type */ > > + spin_lock_irqsave(&report_filterlist_lock, flags); > > + seq_printf(file, "\n%s functions: %s\n", > > + report_filterlist.whitelist ? "whitelisted" : "blacklisted", > > + report_filterlist.used == 0 ? "none" : ""); > > + for (i = 0; i < report_filterlist.used; ++i) > > + seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]); > > + spin_unlock_irqrestore(&report_filterlist_lock, flags); > > + > > + return 0; > > +} > > + > > +static int debugfs_open(struct inode *inode, struct file *file) > > +{ > > + return single_open(file, show_info, NULL); > > +} > > + > > +static ssize_t debugfs_write(struct file *file, const char __user *buf, > > + size_t count, loff_t *off) > > +{ > > + char kbuf[KSYM_NAME_LEN]; > > + char *arg; > > + int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1); > > + > > + if (copy_from_user(kbuf, buf, read_len)) > > + return -EINVAL; > > + kbuf[read_len] = '\0'; > > + arg = strstrip(kbuf); > > + > > + if (!strncmp(arg, "on", sizeof("on") - 1)) > > + WRITE_ONCE(kcsan_enabled, true); > > + else if (!strncmp(arg, "off", sizeof("off") - 1)) > > + WRITE_ONCE(kcsan_enabled, false); > > + else if (!strncmp(arg, "whitelist", sizeof("whitelist") - 1)) > > + set_report_filterlist_whitelist(true); > > + else if (!strncmp(arg, "blacklist", sizeof("blacklist") - 1)) > > + set_report_filterlist_whitelist(false); > > + else if (arg[0] == '!') > > + insert_report_filterlist(&arg[1]); > > + else > > + return -EINVAL; > > + > > + return count; > > +} > > + > > +static const struct file_operations debugfs_ops = { .read = seq_read, > > + .open = debugfs_open, > > + .write = debugfs_write, > > + .release = single_release }; > > + > > +void __init kcsan_debugfs_init(void) > > +{ > > + debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops); > > +} > > diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h > > new file mode 100644 > > index 000000000000..8f9b1ce0e59f > > --- /dev/null > > +++ b/kernel/kcsan/encoding.h > > @@ -0,0 +1,94 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > + > > +#ifndef _MM_KCSAN_ENCODING_H > > +#define _MM_KCSAN_ENCODING_H > > + > > +#include > > +#include > > +#include > > + > > +#include "kcsan.h" > > + > > +#define SLOT_RANGE PAGE_SIZE > > +#define INVALID_WATCHPOINT 0 > > +#define CONSUMED_WATCHPOINT 1 > > + > > +/* > > + * The maximum useful size of accesses for which we set up watchpoints is the > > + * max range of slots we check on an access. > > + */ > > +#define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT)) > > + > > +/* > > + * Number of bits we use to store size info. > > + */ > > +#define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE) > > +/* > > + * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS); > > + * however, most 64-bit architectures do not use the full 64-bit address space. > > + * Also, in order for a false positive to be observable 2 things need to happen: > > + * > > + * 1. different addresses but with the same encoded address race; > > + * 2. and both map onto the same watchpoint slots; > > + * > > + * Both these are assumed to be very unlikely. However, in case it still happens > > + * happens, the report logic will filter out the false positive (see report.c). > > + */ > > +#define WATCHPOINT_ADDR_BITS (BITS_PER_LONG - 1 - WATCHPOINT_SIZE_BITS) > > + > > +/* > > + * Masks to set/retrieve the encoded data. > > + */ > > +#define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG - 1) > > +#define WATCHPOINT_SIZE_MASK \ > > + GENMASK(BITS_PER_LONG - 2, BITS_PER_LONG - 2 - WATCHPOINT_SIZE_BITS) > > +#define WATCHPOINT_ADDR_MASK \ > > + GENMASK(BITS_PER_LONG - 3 - WATCHPOINT_SIZE_BITS, 0) > > + > > +static inline bool check_encodable(unsigned long addr, size_t size) > > +{ > > + return size <= MAX_ENCODABLE_SIZE; > > +} > > + > > +static inline long encode_watchpoint(unsigned long addr, size_t size, > > + bool is_write) > > +{ > > + return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) | > > + (size << WATCHPOINT_ADDR_BITS) | > > + (addr & WATCHPOINT_ADDR_MASK)); > > +} > > + > > +static inline bool decode_watchpoint(long watchpoint, > > + unsigned long *addr_masked, size_t *size, > > + bool *is_write) > > +{ > > + if (watchpoint == INVALID_WATCHPOINT || > > + watchpoint == CONSUMED_WATCHPOINT) > > + return false; > > + > > + *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK; > > + *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> > > + WATCHPOINT_ADDR_BITS; > > + *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK); > > + > > + return true; > > +} > > + > > +/* > > + * Return watchpoint slot for an address. > > + */ > > +static inline int watchpoint_slot(unsigned long addr) > > +{ > > + return (addr / PAGE_SIZE) % KCSAN_NUM_WATCHPOINTS; > > +} > > + > > +static inline bool matching_access(unsigned long addr1, size_t size1, > > + unsigned long addr2, size_t size2) > > +{ > > + unsigned long end_range1 = addr1 + size1 - 1; > > + unsigned long end_range2 = addr2 + size2 - 1; > > + > > + return addr1 <= end_range2 && addr2 <= end_range1; > > +} > > + > > +#endif /* _MM_KCSAN_ENCODING_H */ > > diff --git a/kernel/kcsan/kcsan.c b/kernel/kcsan/kcsan.c > > new file mode 100644 > > index 000000000000..45cf2fffd8a0 > > --- /dev/null > > +++ b/kernel/kcsan/kcsan.c > > @@ -0,0 +1,86 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +/* > > + * The Kernel Concurrency Sanitizer (KCSAN) infrastructure. For more info please > > + * see Documentation/dev-tools/kcsan.rst. > > + */ > > + > > +#include > > + > > +#include "kcsan.h" > > + > > +/* > > + * KCSAN uses the same instrumentation that is emitted by supported compilers > > + * for Thread Sanitizer (TSAN). > > + * > > + * When enabled, the compiler emits instrumentation calls (the functions > > + * prefixed with "__tsan" below) for all loads and stores that it generated; > > + * inline asm is not instrumented. > > + */ > > + > > +#define DEFINE_TSAN_READ_WRITE(size) \ > > + void __tsan_read##size(void *ptr) \ > > + { \ > > + __kcsan_check_read(ptr, size); \ > > + } \ > > + EXPORT_SYMBOL(__tsan_read##size); \ > > + void __tsan_write##size(void *ptr) \ > > + { \ > > + __kcsan_check_write(ptr, size); \ > > + } \ > > + EXPORT_SYMBOL(__tsan_write##size) > > + > > +DEFINE_TSAN_READ_WRITE(1); > > +DEFINE_TSAN_READ_WRITE(2); > > +DEFINE_TSAN_READ_WRITE(4); > > +DEFINE_TSAN_READ_WRITE(8); > > +DEFINE_TSAN_READ_WRITE(16); > > + > > +/* > > + * Not all supported compiler versions distinguish aligned/unaligned accesses, > > + * but e.g. recent versions of Clang do. > > + */ > > +#define DEFINE_TSAN_UNALIGNED_READ_WRITE(size) \ > > + void __tsan_unaligned_read##size(void *ptr) \ > > + { \ > > + __kcsan_check_read(ptr, size); \ > > + } \ > > + EXPORT_SYMBOL(__tsan_unaligned_read##size); \ > > + void __tsan_unaligned_write##size(void *ptr) \ > > + { \ > > + __kcsan_check_write(ptr, size); \ > > + } \ > > + EXPORT_SYMBOL(__tsan_unaligned_write##size) > > + > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(2); > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(4); > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(8); > > +DEFINE_TSAN_UNALIGNED_READ_WRITE(16); > > + > > +void __tsan_read_range(void *ptr, size_t size) > > +{ > > + __kcsan_check_read(ptr, size); > > +} > > +EXPORT_SYMBOL(__tsan_read_range); > > + > > +void __tsan_write_range(void *ptr, size_t size) > > +{ > > + __kcsan_check_write(ptr, size); > > +} > > +EXPORT_SYMBOL(__tsan_write_range); > > + > > +/* > > + * The below are not required KCSAN, but can still be emitted by the compiler. > > + */ > > +void __tsan_func_entry(void *call_pc) > > +{ > > +} > > +EXPORT_SYMBOL(__tsan_func_entry); > > +void __tsan_func_exit(void) > > +{ > > +} > > +EXPORT_SYMBOL(__tsan_func_exit); > > +void __tsan_init(void) > > +{ > > +} > > +EXPORT_SYMBOL(__tsan_init); > > diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h > > new file mode 100644 > > index 000000000000..429479b3041d > > --- /dev/null > > +++ b/kernel/kcsan/kcsan.h > > @@ -0,0 +1,140 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > + > > +#ifndef _MM_KCSAN_KCSAN_H > > +#define _MM_KCSAN_KCSAN_H > > + > > +#include > > + > > +/* > > + * Total number of watchpoints. An address range maps into a specific slot as > > + * specified in `encoding.h`. Although larger number of watchpoints may not even > > + * be usable due to limited thread count, a larger value will improve > > + * performance due to reducing cache-line contention. > > + */ > > +#define KCSAN_NUM_WATCHPOINTS 64 > > + > > +/* > > + * The number of adjacent watchpoints to check; the purpose is 2-fold: > > + * > > + * 1. the address slot is already occupied, check if any adjacent slots are > > + * free; > > + * 2. accesses that straddle a slot boundary due to size that exceeds a > > + * slot's range may check adjacent slots if any watchpoint matches. > > + * > > + * Note that accesses with very large size may still miss a watchpoint; however, > > + * given this should be rare, this is a reasonable trade-off to make, since this > > + * will avoid: > > + * > > + * 1. excessive contention between watchpoint checks and setup; > > + * 2. larger number of simultaneous watchpoints without sacrificing > > + * performance. > > + */ > > +#define KCSAN_CHECK_ADJACENT 1 > > + > > +/* > > + * Globally enable and disable KCSAN. > > + */ > > +extern bool kcsan_enabled; > > + > > +/* > > + * Helper that returns true if access to ptr should be considered as an atomic > > + * access, even though it is not explicitly atomic. > > + */ > > +bool kcsan_is_atomic(const volatile void *ptr); > > + > > +/* > > + * Initialize debugfs file. > > + */ > > +void kcsan_debugfs_init(void); > > + > > +enum kcsan_counter_id { > Labels in enums should be capitalized: > https://www.kernel.org/doc/html/v4.10/process/coding-style.html#macros-enums-and-rtl Done @ v3. > > + /* > > + * Number of watchpoints currently in use. > > + */ > > + kcsan_counter_used_watchpoints, > > + > > + /* > > + * Total number of watchpoints set up. > > + */ > > + kcsan_counter_setup_watchpoints, > > + > > + /* > > + * Total number of data-races. > > + */ > > + kcsan_counter_data_races, > > + > > + /* > > + * Number of times no watchpoints were available. > > + */ > > + kcsan_counter_no_capacity, > > + > > + /* > > + * A thread checking a watchpoint raced with another checking thread; > > + * only one will be reported. > > + */ > > + kcsan_counter_report_races, > > + > > + /* > > + * Observed data value change, but writer thread unknown. > > + */ > > + kcsan_counter_races_unknown_origin, > > + > > + /* > > + * The access cannot be encoded to a valid watchpoint. > > + */ > > + kcsan_counter_unencodable_accesses, > > + > > + /* > > + * Watchpoint encoding caused a watchpoint to fire on mismatching > > + * accesses. > > + */ > > + kcsan_counter_encoding_false_positives, > > + > > + kcsan_counter_count, /* number of counters */ > > +}; > > + > > +/* > > + * Increment/decrement counter with given id; avoid calling these in fast-path. > > + */ > > +void kcsan_counter_inc(enum kcsan_counter_id id); > > +void kcsan_counter_dec(enum kcsan_counter_id id); > > + > > +/* > > + * Returns true if data-races in the function symbol that maps to addr (offsets > > + * are ignored) should *not* be reported. > > + */ > > +bool kcsan_skip_report(unsigned long func_addr); > > + > > +enum kcsan_report_type { > > + /* > > + * The thread that set up the watchpoint and briefly stalled was > > + * signalled that another thread triggered the watchpoint, and thus a > > + * race was encountered. > > + */ > > + kcsan_report_race_setup, > > + > > + /* > > + * A thread encountered a watchpoint for the access, therefore a race > > + * was encountered. > > + */ > > + kcsan_report_race_check, > > + > > + /* > > + * A thread encountered a watchpoint for the access, but the other > > + * racing thread can no longer be signaled that a race occurred. > > + */ > > + kcsan_report_race_check_race, > > + > > + /* > > + * No other thread was observed to race with the access, but the data > > + * value before and after the stall differs. > > + */ > > + kcsan_report_race_unknown_origin, > > +}; > > +/* > > + * Print a race report from thread that encountered the race. > > + */ > > +void kcsan_report(const volatile void *ptr, size_t size, bool is_write, > > + int cpu_id, enum kcsan_report_type type); > > + > > +#endif /* _MM_KCSAN_KCSAN_H */ > > diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c > > new file mode 100644 > > index 000000000000..517db539e4e7 > > --- /dev/null > > +++ b/kernel/kcsan/report.c > > @@ -0,0 +1,306 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#include "kcsan.h" > > +#include "encoding.h" > > + > > +/* > > + * Max. number of stack entries to show in the report. > > + */ > > +#define NUM_STACK_ENTRIES 16 > > + > > +/* > > + * Other thread info: communicated from other racing thread to thread that set > > + * up the watchpoint, which then prints the complete report atomically. Only > > + * need one struct, as all threads should to be serialized regardless to print > > + * the reports, with reporting being in the slow-path. > > + */ > > +static struct { > > + const volatile void *ptr; > > + size_t size; > > + bool is_write; > > + int task_pid; > > + int cpu_id; > > + unsigned long stack_entries[NUM_STACK_ENTRIES]; > > + int num_stack_entries; > > +} other_info = { .ptr = NULL }; > > + > > +static DEFINE_SPINLOCK(other_info_lock); > > +static DEFINE_SPINLOCK(report_lock); > > + > > +static bool set_or_lock_other_info(unsigned long *flags, > > + const volatile void *ptr, size_t size, > > + bool is_write, int cpu_id, > > + enum kcsan_report_type type) > > +{ > > + if (type != kcsan_report_race_check && type != kcsan_report_race_setup) > > + return true; > > + > > + for (;;) { > > + spin_lock_irqsave(&other_info_lock, *flags); > > + > > + switch (type) { > > + case kcsan_report_race_check: > > + if (other_info.ptr != NULL) { > > + /* still in use, retry */ > > + break; > > + } > > + other_info.ptr = ptr; > > + other_info.size = size; > > + other_info.is_write = is_write; > > + other_info.task_pid = > > + in_task() ? task_pid_nr(current) : -1; > > + other_info.cpu_id = cpu_id; > > + other_info.num_stack_entries = stack_trace_save( > > + other_info.stack_entries, NUM_STACK_ENTRIES, 1); > > + /* > > + * other_info may now be consumed by thread we raced > > + * with. > > + */ > > + spin_unlock_irqrestore(&other_info_lock, *flags); > > + return false; > > + > > + case kcsan_report_race_setup: > > + if (other_info.ptr == NULL) > > + break; /* no data available yet, retry */ > > + > > + /* > > + * First check if matching based on how watchpoint was > > + * encoded. > > + */ > > + if (!matching_access((unsigned long)other_info.ptr & > > + WATCHPOINT_ADDR_MASK, > > + other_info.size, > > + (unsigned long)ptr & > > + WATCHPOINT_ADDR_MASK, > > + size)) > > + break; /* mismatching access, retry */ > > + > > + if (!matching_access((unsigned long)other_info.ptr, > > + other_info.size, > > + (unsigned long)ptr, size)) { > > + /* > > + * If the actual accesses to not match, this was > > + * a false positive due to watchpoint encoding. > > + */ > > + other_info.ptr = NULL; /* mark for reuse */ > > + kcsan_counter_inc( > > + kcsan_counter_encoding_false_positives); > > + spin_unlock_irqrestore(&other_info_lock, > > + *flags); > > + return false; > > + } > > + > > + /* > > + * Matching access: keep other_info locked, as this > > + * thread uses it to print the full report; unlocked in > > + * end_report. > > + */ > > + return true; > > + > > + default: > > + BUG(); > > + } > > + > > + spin_unlock_irqrestore(&other_info_lock, *flags); > > + } > > +} > > + > > +static void start_report(unsigned long *flags, enum kcsan_report_type type) > > +{ > > + switch (type) { > > + case kcsan_report_race_setup: > > + /* irqsaved already via other_info_lock */ > > + spin_lock(&report_lock); > > + break; > > + > > + case kcsan_report_race_unknown_origin: > > + spin_lock_irqsave(&report_lock, *flags); > > + break; > > + > > + default: > > + BUG(); > > + } > > +} > > + > > +static void end_report(unsigned long *flags, enum kcsan_report_type type) > > +{ > > + switch (type) { > > + case kcsan_report_race_setup: > > + other_info.ptr = NULL; /* mark for reuse */ > > + spin_unlock(&report_lock); > > + spin_unlock_irqrestore(&other_info_lock, *flags); > > + break; > > + > > + case kcsan_report_race_unknown_origin: > > + spin_unlock_irqrestore(&report_lock, *flags); > > + break; > > + > > + default: > > + BUG(); > > + } > > +} > > + > > +static const char *get_access_type(bool is_write) > > +{ > > + return is_write ? "write" : "read"; > > +} > > + > > +/* Return thread description: in task or interrupt. */ > > +static const char *get_thread_desc(int task_id) > > +{ > > + if (task_id != -1) { > > + static char buf[32]; /* safe: protected by report_lock */ > > + > > + snprintf(buf, sizeof(buf), "task %i", task_id); > > + return buf; > > + } > > + return in_nmi() ? "NMI" : "interrupt"; > > +} > > + > > +/* Helper to skip KCSAN-related functions in stack-trace. */ > > +static int get_stack_skipnr(unsigned long stack_entries[], int num_entries) > > +{ > > + char buf[64]; > > + int skip = 0; > > + > > + for (; skip < num_entries; ++skip) { > > + snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]); > > + if (!strnstr(buf, "csan_", sizeof(buf)) && > > + !strnstr(buf, "tsan_", sizeof(buf)) && > > + !strnstr(buf, "_once_size", sizeof(buf))) { > > + break; > > + } > > + } > > + return skip; > > +} > FWIW another option is to put all KCSAN-related functions in a > separate code section and check if the function addresses are in the > address range belonging to that section. > This will work even with non-symbolized stacks. Thanks for the suggestion. Is it worth it, i.e. will it simplify the design and code? If it simplifies the design (or makes the fast-path significantly faster), then yes, but otherwise I prefer the simplest possible solution here. AFAIK, it will not make it simpler nor faster. Using non-symbolized stacks should not be the common use-case (how to usefully debug any data-race?). > > +/* Compares symbolized strings of addr1 and addr2. */ > > +static int sym_strcmp(void *addr1, void *addr2) > > +{ > > + char buf1[64]; > > + char buf2[64]; > > + > > + snprintf(buf1, sizeof(buf1), "%pS", addr1); > > + snprintf(buf2, sizeof(buf2), "%pS", addr2); > > + return strncmp(buf1, buf2, sizeof(buf1)); > > +} > > + > > +/* > > + * Returns true if a report was generated, false otherwise. > > + */ > > +static bool print_summary(const volatile void *ptr, size_t size, bool is_write, > > + int cpu_id, enum kcsan_report_type type) > > +{ > > + unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 }; > > + int num_stack_entries = > > + stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1); > > + int skipnr = get_stack_skipnr(stack_entries, num_stack_entries); > > + int other_skipnr; > > + > > + /* Check if the top stackframe is in a blacklisted function. */ > > + if (kcsan_skip_report(stack_entries[skipnr])) > > + return false; > > + if (type == kcsan_report_race_setup) { > > + other_skipnr = get_stack_skipnr(other_info.stack_entries, > > + other_info.num_stack_entries); > > + if (kcsan_skip_report(other_info.stack_entries[other_skipnr])) > > + return false; > > + } > > + > > + /* Print report header. */ > > + pr_err("==================================================================\n"); > > + switch (type) { > > + case kcsan_report_race_setup: { > > + void *this_fn = (void *)stack_entries[skipnr]; > > + void *other_fn = (void *)other_info.stack_entries[other_skipnr]; > > + int cmp; > > + > > + /* > > + * Order functions lexographically for consistent bug titles. > > + * Do not print offset of functions to keep title short. > > + */ > > + cmp = sym_strcmp(other_fn, this_fn); > > + pr_err("BUG: KCSAN: data-race in %ps / %ps\n", > > + cmp < 0 ? other_fn : this_fn, > > + cmp < 0 ? this_fn : other_fn); > > + } break; > > + > > + case kcsan_report_race_unknown_origin: > > + pr_err("BUG: KCSAN: data-race in %pS\n", > > + (void *)stack_entries[skipnr]); > > + break; > > + > > + default: > > + BUG(); > > + } > > + > > + pr_err("\n"); > > + > > + /* Print information about the racing accesses. */ > > + switch (type) { > > + case kcsan_report_race_setup: > > + pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", > > + get_access_type(other_info.is_write), other_info.ptr, > > + other_info.size, get_thread_desc(other_info.task_pid), > > + other_info.cpu_id); > > + > > + /* Print the other thread's stack trace. */ > > + stack_trace_print(other_info.stack_entries + other_skipnr, > > + other_info.num_stack_entries - other_skipnr, > > + 0); > > + > > + pr_err("\n"); > > + pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", > > + get_access_type(is_write), ptr, size, > > + get_thread_desc(in_task() ? task_pid_nr(current) : -1), > > + cpu_id); > > + break; > > + > > + case kcsan_report_race_unknown_origin: > > + pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n", > > + get_access_type(is_write), ptr, size, > > + get_thread_desc(in_task() ? task_pid_nr(current) : -1), > > + cpu_id); > > + break; > > + > > + default: > > + BUG(); > > + } > > + /* Print stack trace of this thread. */ > > + stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, > > + 0); > > + > > + /* Print report footer. */ > > + pr_err("\n"); > > + pr_err("Reported by Kernel Concurrency Sanitizer on:\n"); > > + dump_stack_print_info(KERN_DEFAULT); > > + pr_err("==================================================================\n"); > > + > > + return true; > > +} > > + > > +void kcsan_report(const volatile void *ptr, size_t size, bool is_write, > > + int cpu_id, enum kcsan_report_type type) > > +{ > > + unsigned long flags = 0; > > + > > + if (type == kcsan_report_race_check_race) > > + return; > > + > > + kcsan_disable_current(); > > + if (set_or_lock_other_info(&flags, ptr, size, is_write, cpu_id, type)) { > > + start_report(&flags, type); > > + if (print_summary(ptr, size, is_write, cpu_id, type) && > > + panic_on_warn) > > + panic("panic_on_warn set ...\n"); > > + > > + end_report(&flags, type); > > + } > > + kcsan_enable_current(); > > +} > > diff --git a/kernel/kcsan/test.c b/kernel/kcsan/test.c > > new file mode 100644 > > index 000000000000..68c896a24529 > > --- /dev/null > > +++ b/kernel/kcsan/test.c > > @@ -0,0 +1,117 @@ > > +// SPDX-License-Identifier: GPL-2.0 > IIRC checkpatch.pl requires all SPDX headers to look like this one > (C++-style, not C-style). > Please double check and fix the headers in other files if necessary. Checkpatch is happy. // for .c, and /**/ for .h. > This file might also use some comments, now it's not easy to > understand what it's testing. Done @ v3. > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#include "encoding.h" > > + > > +#define ITERS_PER_TEST 2000 > > + > > +/* Test requirements. */ > > +static bool test_requires(void) > > +{ > > + /* random should be initialized */ > > + return prandom_u32() + prandom_u32() != 0; > > +} > > + > > +/* Test watchpoint encode and decode. */ > > +static bool test_encode_decode(void) > > +{ > > + int i; > > + > > + for (i = 0; i < ITERS_PER_TEST; ++i) { > > + size_t size = prandom_u32() % MAX_ENCODABLE_SIZE + 1; > > + bool is_write = prandom_u32() % 2; > > + unsigned long addr; > > + > > + prandom_bytes(&addr, sizeof(addr)); > > + if (WARN_ON(!check_encodable(addr, size))) > > + return false; > > + > > + /* encode and decode */ > > + { > > + const long encoded_watchpoint = > > + encode_watchpoint(addr, size, is_write); > > + unsigned long verif_masked_addr; > > + size_t verif_size; > > + bool verif_is_write; > > + > > + /* check special watchpoints */ > > + if (WARN_ON(decode_watchpoint( > > + INVALID_WATCHPOINT, &verif_masked_addr, > > + &verif_size, &verif_is_write))) > > + return false; > > + if (WARN_ON(decode_watchpoint( > > + CONSUMED_WATCHPOINT, &verif_masked_addr, > > + &verif_size, &verif_is_write))) > > + return false; > > + > > + /* check decoding watchpoint returns same data */ > > + if (WARN_ON(!decode_watchpoint( > > + encoded_watchpoint, &verif_masked_addr, > > + &verif_size, &verif_is_write))) > > + return false; > > + if (WARN_ON(verif_masked_addr != > > + (addr & WATCHPOINT_ADDR_MASK))) > > + goto fail; > > + if (WARN_ON(verif_size != size)) > > + goto fail; > > + if (WARN_ON(is_write != verif_is_write)) > > + goto fail; > > + > > + continue; > > +fail: > > + pr_err("%s fail: %s %zu bytes @ %lx -> encoded: %lx -> %s %zu bytes @ %lx\n", > > + __func__, is_write ? "write" : "read", size, > > + addr, encoded_watchpoint, > > + verif_is_write ? "write" : "read", verif_size, > > + verif_masked_addr); > > + return false; > > + } > > + } > > + > > + return true; > > +} > > + > > +static bool test_matching_access(void) > > +{ > > + if (WARN_ON(!matching_access(10, 1, 10, 1))) > > + return false; > > + if (WARN_ON(!matching_access(10, 2, 11, 1))) > > + return false; > > + if (WARN_ON(!matching_access(10, 1, 9, 2))) > > + return false; > > + if (WARN_ON(matching_access(10, 1, 11, 1))) > > + return false; > > + if (WARN_ON(matching_access(9, 1, 10, 1))) > > + return false; > > + return true; > > +} > > + > > +static int __init kcsan_selftest(void) > > +{ > > + int passed = 0; > > + int total = 0; > > + > > +#define RUN_TEST(do_test) \ > > + do { \ > > + ++total; \ > > + if (do_test()) \ > > + ++passed; \ > > + else \ > > + pr_err("KCSAN selftest: " #do_test " failed"); \ > > + } while (0) > > + > > + RUN_TEST(test_requires); > > + RUN_TEST(test_encode_decode); > > + RUN_TEST(test_matching_access); > > + > > + pr_info("KCSAN selftest: %d/%d tests passed\n", passed, total); > > + if (passed != total) > > + panic("KCSAN selftests failed"); > > + return 0; > > +} > > +postcore_initcall(kcsan_selftest); > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 93d97f9b0157..35accd1d93de 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -2086,6 +2086,8 @@ source "lib/Kconfig.kgdb" > > > > source "lib/Kconfig.ubsan" > > > > +source "lib/Kconfig.kcsan" > > + > > config ARCH_HAS_DEVMEM_IS_ALLOWED > > bool > > > > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan > > new file mode 100644 > > index 000000000000..3e1f1acfb24b > > --- /dev/null > > +++ b/lib/Kconfig.kcsan > > @@ -0,0 +1,88 @@ > > +# SPDX-License-Identifier: GPL-2.0-only > > + > > +config HAVE_ARCH_KCSAN > > + bool > > + > > +menuconfig KCSAN > > + bool "KCSAN: watchpoint-based dynamic data-race detector" > > + depends on HAVE_ARCH_KCSAN && !KASAN && STACKTRACE > > + default n > > + help > > + Kernel Concurrency Sanitizer is a dynamic data-race detector, which > > + uses a watchpoint-based sampling approach to detect races. > > + > > +if KCSAN > > + > > +config KCSAN_SELFTEST > > + bool "KCSAN: perform short selftests on boot" > > + default y > > + help > > + Run KCSAN selftests on boot. On test failure, causes kernel to panic. > > + > > +config KCSAN_EARLY_ENABLE > > + bool "KCSAN: early enable" > > + default y > > + help > > + If KCSAN should be enabled globally as soon as possible. KCSAN can > > + later be enabled/disabled via debugfs. > > + > > +config KCSAN_UDELAY_MAX_TASK > > + int "KCSAN: maximum delay in microseconds (for tasks)" > > + default 80 > > + help > > + For tasks, the max. microsecond delay after setting up a watchpoint. > > + > > +config KCSAN_UDELAY_MAX_INTERRUPT > > + int "KCSAN: maximum delay in microseconds (for interrupts)" > > + default 20 > > + help > > + For interrupts, the max. microsecond delay after setting up a watchpoint. > > + > > +config KCSAN_DELAY_RANDOMIZE > > + bool "KCSAN: randomize delays" > > + default y > > + help > > + If delays should be randomized; if false, the chosen delay is simply > > + the maximum values defined above. > > + > > +config KCSAN_WATCH_SKIP_INST > > + int "KCSAN: watchpoint instruction skip" > > + default 2000 > > + help > > + The number of per-CPU memory operations to skip watching, before > > + another watchpoint is set up; in other words, 1 in > > + KCSAN_WATCH_SKIP_INST per-CPU memory operations are used to set up a > > + watchpoint. A smaller value results in more aggressive race > > + detection, whereas a larger value improves system performance at the > > + cost of missing some races. > > + > > +config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN > > + bool "KCSAN: report races of unknown origin" > > + default y > > + help > > + If KCSAN should report races where only one access is known, and the > > + conflicting access is of unknown origin. This type of race is > > + reported if it was only possible to infer a race due to a data-value > > + change while an access is being delayed on a watchpoint. > > + > > +config KCSAN_IGNORE_ATOMICS > > + bool "KCSAN: do not instrument marked atomic accesses" > > + default n > > + help > > + If enabled, never instruments marked atomic accesses. This results in > > + not reporting data-races where one access is atomic and the other is > > + a plain access. > > + > Isn't it better to decide at runtime, whether we want to ignore atomics or not? See below. > > +config KCSAN_PLAIN_WRITE_PRETEND_ONCE > > + bool "KCSAN: pretend plain writes are WRITE_ONCE" > > + default n > > + help > > + This option makes KCSAN pretend that all plain writes are WRITE_ONCE. > > + This option should only be used to prune initial data-races found in > > + existing code. > Overall, I think it's better to make most of these configs boot-time flags. > This way one won't need to rebuild the kernel every time they want to > turn some option on or off. >From a design point of view, this complicates things on several fronts. For one I would prefer having config options in one place, however, most of these were added to "tame" syzbot, and keep reporting volume initially low. I do not expect these to be switched frequently, and for simplicity sake and to optimize for the common use-case, it'll be better to keep it as-is. Eventually, these might even go away completely. I will add a comment to that effect above these options for v3. > > +config KCSAN_DEBUG > > + bool "Debugging of KCSAN internals" > > + default n > > + > > +endif # KCSAN > > diff --git a/lib/Makefile b/lib/Makefile > > index c5892807e06f..778ab704e3ad 100644 > > --- a/lib/Makefile > > +++ b/lib/Makefile > > @@ -24,6 +24,9 @@ KASAN_SANITIZE_string.o := n > > CFLAGS_string.o := $(call cc-option, -fno-stack-protector) > > endif > > > > +# Used by KCSAN while enabled, avoid recursion. > > +KCSAN_SANITIZE_random32.o := n > > + > > lib-y := ctype.o string.o vsprintf.o cmdline.o \ > > rbtree.o radix-tree.o timerqueue.o xarray.o \ > > idr.o extable.o \ > > diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan > > new file mode 100644 > > index 000000000000..caf1111a28ae > > --- /dev/null > > +++ b/scripts/Makefile.kcsan > > @@ -0,0 +1,6 @@ > > +# SPDX-License-Identifier: GPL-2.0 > > +ifdef CONFIG_KCSAN > > + > > +CFLAGS_KCSAN := -fsanitize=thread > > + > > +endif # CONFIG_KCSAN > > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib > > index 179d55af5852..0e78abab7d83 100644 > > --- a/scripts/Makefile.lib > > +++ b/scripts/Makefile.lib > > @@ -152,6 +152,16 @@ _c_flags += $(if $(patsubst n%,, \ > > $(CFLAGS_KCOV)) > > endif > > > > +# > > +# Enable ConcurrencySanitizer flags for kernel except some files or directories > "KernelConcurrencySanitizer" or "Kernel Concurrency Sanitizer", maybe? Done @ v3. > > +# we don't want to check (depends on variables KCSAN_SANITIZE_obj.o, KCSAN_SANITIZE) > > +# > > +ifeq ($(CONFIG_KCSAN),y) > > +_c_flags += $(if $(patsubst n%,, \ > > + $(KCSAN_SANITIZE_$(basetarget).o)$(KCSAN_SANITIZE)y), \ > > + $(CFLAGS_KCSAN)) > > +endif > > + > > # $(srctree)/$(src) for including checkin headers from generated source files > > # $(objtree)/$(obj) for including generated headers from checkin source files > > ifeq ($(KBUILD_EXTMOD),) > > -- > > 2.23.0.866.gb869b98d4c-goog > > Thanks for your comments! -- Marco