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=-20.4 required=3.0 tests=BAYES_00,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, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham 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 A495AC4363D for ; Tue, 6 Oct 2020 22:55:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E7CA20BED for ; Tue, 6 Oct 2020 22:55:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="MtWR3Vyu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726722AbgJFWzE (ORCPT ); Tue, 6 Oct 2020 18:55:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725996AbgJFWzC (ORCPT ); Tue, 6 Oct 2020 18:55:02 -0400 Received: from mail-wm1-x341.google.com (mail-wm1-x341.google.com [IPv6:2a00:1450:4864:20::341]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8F064C061755 for ; Tue, 6 Oct 2020 15:55:02 -0700 (PDT) Received: by mail-wm1-x341.google.com with SMTP id d3so420088wma.4 for ; Tue, 06 Oct 2020 15:55:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=HGCVKyGQYZlN2d0OUVMXYRPm5j+ZPoa8A5kyMh5F4+U=; b=MtWR3VyubrBnus+o/vh7gAp/nETf7cvtPg3bsbRbOoaBmBVPhDQViSLg0Sm+d6t2EV 1sFIztChA/8yNE6rZ+JfUbQozKN15UNruTKS97DMZO4BZGRcBJvSmnDMHH+Buvegorea uSJQp4hPC6vU1v94lar4/E34Wr1vxdJdwFPmNIUzMzod7kaC4cf+wsboZLdjioe0CIyN cdsHpaBlZizKsh1dmmSC1BTO2hcuDNe5Wuit40HFnaqcaVXxzYTB2VEYAwFzXLzXnRjN psNmrtLFyhE7lIzGaniy1ENf+7jOFbQs33UO6gsayyuDFY4MkBJPoFlLDmSfRDWIwUJI zCDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=HGCVKyGQYZlN2d0OUVMXYRPm5j+ZPoa8A5kyMh5F4+U=; b=mnHo0SI64zE8B7QkdJyoJIuFUIQINsv+XfI9oh4nWJCpEyhR6jT52yxY0FJAdbegwA gCnPkPgSbNdn8/grEFSWVyugmy7vwkkkqJOT2A2nceGkzziAmRgjCYeHEOrW3v56YaDx 5Ej25md5qUixVS6TTH6Upg3cCLoDSaSW+mP6qLMmLvzi27w8qsrrXopS8ohACdruxPrT 3G6PmrlqKNLn/E7ThvzCESg0X0Bix0gGOnx9ZPuaCUeeStIu9pX8crXVhhVGey3g2bqa G+BHPRcFxxU9PPXy0TBqyEc/UFgngakIdLV4NvYlsW3RkxvvZNICgYl7+zChQApKQNPV X/Tw== X-Gm-Message-State: AOAM533t+asqiSwwZKCzPXWSJvTVLfnfmZIFFV6q/3Du1V0e+lLZuFL3 cxl9z/K2bzkuUkuXU4qaKTp9yg== X-Google-Smtp-Source: ABdhPJxtwY+EEZDUG+ByVJbphRcGc6RU0rLKiFkJaQUAspMbv4Mof8L7Z40rGPrOffzEGzMOeng9Ig== X-Received: by 2002:a05:600c:2902:: with SMTP id i2mr167748wmd.31.1602024900851; Tue, 06 Oct 2020 15:55:00 -0700 (PDT) Received: from localhost ([2a02:168:96c5:1:55ed:514f:6ad7:5bcc]) by smtp.gmail.com with ESMTPSA id i15sm243602wrb.91.2020.10.06.15.55.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Oct 2020 15:55:00 -0700 (PDT) From: Jann Horn To: Andrew Morton , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, "Eric W . Biederman" , Michel Lespinasse , Mauro Carvalho Chehab , Sakari Ailus , Jeff Dike , Richard Weinberger , Anton Ivanov , linux-um@lists.infradead.org, Jason Gunthorpe , John Hubbard Subject: [PATCH v2 1/2] mmap locking API: Order lock of nascent mm outside lock of live mm Date: Wed, 7 Oct 2020 00:54:49 +0200 Message-Id: <20201006225450.751742-2-jannh@google.com> X-Mailer: git-send-email 2.28.0.806.g8561365e88-goog In-Reply-To: <20201006225450.751742-1-jannh@google.com> References: <20201006225450.751742-1-jannh@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Until now, the mmap lock of the nascent mm was ordered inside the mmap lock of the old mm (in dup_mmap() and in UML's activate_mm()). A following patch will change the exec path to very broadly lock the nascent mm, but fine-grained locking should still work at the same time for the old mm. In particular, mmap locking calls are hidden behind the copy_from_user() calls and such that are reached through functions like copy_strings() - when a page fault occurs on a userspace memory access, the mmap lock will be taken. To do this in a way that lockdep is happy about, let's turn around the lock ordering in both places that currently nest the locks. Since SINGLE_DEPTH_NESTING is normally used for the inner nesting layer, make up our own lock subclass MMAP_LOCK_SUBCLASS_NASCENT and use that instead. The added locking calls in exec_mmap() are temporary; the following patch will move the locking out of exec_mmap(). Signed-off-by: Jann Horn --- arch/um/include/asm/mmu_context.h | 3 +-- fs/exec.c | 4 ++++ include/linux/mmap_lock.h | 23 +++++++++++++++++++++-- kernel/fork.c | 7 ++----- 4 files changed, 28 insertions(+), 9 deletions(-) diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h index 17ddd4edf875..c13bc5150607 100644 --- a/arch/um/include/asm/mmu_context.h +++ b/arch/um/include/asm/mmu_context.h @@ -48,9 +48,8 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new) * when the new ->mm is used for the first time. */ __switch_mm(&new->context.id); - mmap_write_lock_nested(new, SINGLE_DEPTH_NESTING); + mmap_assert_write_locked(new); uml_setup_stubs(new); - mmap_write_unlock(new); } static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, diff --git a/fs/exec.c b/fs/exec.c index a91003e28eaa..229dbc7aa61a 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1114,6 +1114,8 @@ static int exec_mmap(struct mm_struct *mm) if (ret) return ret; + mmap_write_lock_nascent(mm); + if (old_mm) { /* * Make sure that if there is a core dump in progress @@ -1125,6 +1127,7 @@ static int exec_mmap(struct mm_struct *mm) if (unlikely(old_mm->core_state)) { mmap_read_unlock(old_mm); mutex_unlock(&tsk->signal->exec_update_mutex); + mmap_write_unlock(mm); return -EINTR; } } @@ -1138,6 +1141,7 @@ static int exec_mmap(struct mm_struct *mm) tsk->mm->vmacache_seqnum = 0; vmacache_flush(tsk); task_unlock(tsk); + mmap_write_unlock(mm); if (old_mm) { mmap_read_unlock(old_mm); BUG_ON(active_mm != old_mm); diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 0707671851a8..24de1fe99ee4 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -3,6 +3,18 @@ #include +/* + * Lock subclasses for the mmap_lock. + * + * MMAP_LOCK_SUBCLASS_NASCENT is for core kernel code that wants to lock an mm + * that is still being constructed and wants to be able to access the active mm + * normally at the same time. It nests outside MMAP_LOCK_SUBCLASS_NORMAL. + */ +enum { + MMAP_LOCK_SUBCLASS_NORMAL = 0, + MMAP_LOCK_SUBCLASS_NASCENT +}; + #define MMAP_LOCK_INITIALIZER(name) \ .mmap_lock = __RWSEM_INITIALIZER((name).mmap_lock), @@ -16,9 +28,16 @@ static inline void mmap_write_lock(struct mm_struct *mm) down_write(&mm->mmap_lock); } -static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass) +/* + * Lock an mm_struct that is still being set up (during fork or exec). + * This nests outside the mmap locks of live mm_struct instances. + * No interruptible/killable versions exist because at the points where you're + * supposed to use this helper, the mm isn't visible to anything else, so we + * expect the mmap_lock to be uncontended. + */ +static inline void mmap_write_lock_nascent(struct mm_struct *mm) { - down_write_nested(&mm->mmap_lock, subclass); + down_write_nested(&mm->mmap_lock, MMAP_LOCK_SUBCLASS_NASCENT); } static inline int mmap_write_lock_killable(struct mm_struct *mm) diff --git a/kernel/fork.c b/kernel/fork.c index da8d360fb032..db67eb4ac7bd 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -474,6 +474,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, unsigned long charge; LIST_HEAD(uf); + mmap_write_lock_nascent(mm); uprobe_start_dup_mmap(); if (mmap_write_lock_killable(oldmm)) { retval = -EINTR; @@ -481,10 +482,6 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, } flush_cache_dup_mm(oldmm); uprobe_dup_mmap(oldmm, mm); - /* - * Not linked in yet - no deadlock potential: - */ - mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING); /* No ordering required: file already has been exposed. */ RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm)); @@ -600,12 +597,12 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, /* a new mm has just been created */ retval = arch_dup_mmap(oldmm, mm); out: - mmap_write_unlock(mm); flush_tlb_mm(oldmm); mmap_write_unlock(oldmm); dup_userfaultfd_complete(&uf); fail_uprobe_end: uprobe_end_dup_mmap(); + mmap_write_unlock(mm); return retval; fail_nomem_anon_vma_fork: mpol_put(vma_policy(tmp)); -- 2.28.0.806.g8561365e88-goog