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, URIBL_BLOCKED,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 1A450C4363D for ; Tue, 6 Oct 2020 22:55:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFEB3208C7 for ; Tue, 6 Oct 2020 22:55:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="k8l5gHBu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727191AbgJFWzJ (ORCPT ); Tue, 6 Oct 2020 18:55:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725996AbgJFWzG (ORCPT ); Tue, 6 Oct 2020 18:55:06 -0400 Received: from mail-wr1-x444.google.com (mail-wr1-x444.google.com [IPv6:2a00:1450:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3279C061755 for ; Tue, 6 Oct 2020 15:55:04 -0700 (PDT) Received: by mail-wr1-x444.google.com with SMTP id n18so22520wrs.5 for ; Tue, 06 Oct 2020 15:55:04 -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=ZE/wKx/2RmNzMs8AoG4OykxIKmOmK9f6qquh+OkR+3A=; b=k8l5gHBu8FLs9Pi1ZWEnxYCUxxmeO6LjSOLKBlTXhxesA30vKQZ1TbOHjgA4/Vxkiu sIZCzhYXm+gsp4aTSWTbAOo3QGodZRtXsPWwjT+62xhCCfGtc9p1GtFEptQ6FIgKmCVE RWo2wLMqH5IRS9hU/QluO6sQpfxOjYGXBg+D8EX9FrvnYQVEYdhem2tfI/8vOI3r79Lv BzWUPsNp636ZRWg+DwQUXSGBOuw5/NZIxUAXtgr5II1G1jjx2Q5/FRzbfXddYePupuNQ WCC2TqJ7L/FHzJOawmS0uel0FSEauRpWzkdNYVGfB50abXfAnmt2aKIL+RuQ3NIGZPS2 PKdA== 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=ZE/wKx/2RmNzMs8AoG4OykxIKmOmK9f6qquh+OkR+3A=; b=qR3Kj26yqnIDR0O5BbmJebLW6HVb2OjLJDOPWiBAzVWCRO1s3/SMTKE1UZfrAmmrzC 60WacfvHRkOrT3f3YhrdyMqzb2m7+utNiDA4iBT6O73fdy9TQKVF42RTDOnrg+UYw4eG ndbbOczWKuz72TPBqgQXWgYElYOg8pls+xxFCxeEPxFfG0/L1rU/Of6KZNCyoNIU7ze6 1dQzvr4f0zYhK5uwVHOQOKvcBwAlFu5+ibahht9i5dO8cB87piCVmKcB6IdB93UGmOFB AEH/uymFNCq/mURTSNdamu4ihI1XWBsazpd89j7q8HK66gryHGCnU+/Srzji6lxOrgDZ klJw== X-Gm-Message-State: AOAM533xOItSooqEqnsEO9MqKJZpVQ9XT2zzvmP7n7NcHUZkWi7j0x6f tv2DIIm23jYAM7M3ViOvGFN6MQ== X-Google-Smtp-Source: ABdhPJzjkNN/QpBwkc7ric2cIHgfEVwzyvIhc8OstjwlEId4qz1orekL0RfkqLjL7OfsBD4AfXnEzA== X-Received: by 2002:adf:e70a:: with SMTP id c10mr156257wrm.425.1602024903367; Tue, 06 Oct 2020 15:55:03 -0700 (PDT) Received: from localhost ([2a02:168:96c5:1:55ed:514f:6ad7:5bcc]) by smtp.gmail.com with ESMTPSA id y11sm310504wrs.16.2020.10.06.15.55.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Oct 2020 15:55:02 -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 2/2] exec: Broadly lock nascent mm until setup_arg_pages() Date: Wed, 7 Oct 2020 00:54:50 +0200 Message-Id: <20201006225450.751742-3-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 While AFAIK there currently is nothing that can modify the VMA tree of a new mm until userspace has started running under the mm, we should properly lock the mm here anyway, both to keep lockdep happy when adding locking assertions and to be safe in the future in case someone e.g. decides to permit VMA-tree-mutating operations in process_madvise_behavior_valid(). The goal of this patch is to broadly lock the nascent mm in the exec path, from around the time it is created all the way to the end of setup_arg_pages() (because setup_arg_pages() accesses bprm->vma). As long as the mm is write-locked, keep it around in bprm->mm, even after it has been installed on the task (with an extra reference on the mm, to reduce complexity in free_bprm()). After setup_arg_pages(), we have to unlock the mm so that APIs such as copy_to_user() will work in the following binfmt-specific setup code. Suggested-by: Jason Gunthorpe Suggested-by: Michel Lespinasse Signed-off-by: Jann Horn --- fs/exec.c | 68 ++++++++++++++++++++--------------------- include/linux/binfmts.h | 2 +- 2 files changed, 35 insertions(+), 35 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 229dbc7aa61a..fe11d77e397a 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -254,11 +254,6 @@ static int __bprm_mm_init(struct linux_binprm *bprm) return -ENOMEM; vma_set_anonymous(vma); - if (mmap_write_lock_killable(mm)) { - err = -EINTR; - goto err_free; - } - /* * Place the stack at the largest stack address the architecture * supports. Later, we'll move this to an appropriate place. We don't @@ -276,12 +271,9 @@ static int __bprm_mm_init(struct linux_binprm *bprm) goto err; mm->stack_vm = mm->total_vm = 1; - mmap_write_unlock(mm); bprm->p = vma->vm_end - sizeof(void *); return 0; err: - mmap_write_unlock(mm); -err_free: bprm->vma = NULL; vm_area_free(vma); return err; @@ -364,9 +356,9 @@ static int bprm_mm_init(struct linux_binprm *bprm) struct mm_struct *mm = NULL; bprm->mm = mm = mm_alloc(); - err = -ENOMEM; if (!mm) - goto err; + return -ENOMEM; + mmap_write_lock_nascent(mm); /* Save current stack limit for all calculations made during exec. */ task_lock(current->group_leader); @@ -374,17 +366,12 @@ static int bprm_mm_init(struct linux_binprm *bprm) task_unlock(current->group_leader); err = __bprm_mm_init(bprm); - if (err) - goto err; - - return 0; - -err: - if (mm) { - bprm->mm = NULL; - mmdrop(mm); - } + if (!err) + return 0; + bprm->mm = NULL; + mmap_write_unlock(mm); + mmdrop(mm); return err; } @@ -735,6 +722,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift) /* * Finalizes the stack vm_area_struct. The flags and permissions are updated, * the stack is optionally relocated, and some extra space is added. + * At the end of this, the mm_struct will be unlocked on success. */ int setup_arg_pages(struct linux_binprm *bprm, unsigned long stack_top, @@ -787,9 +775,6 @@ int setup_arg_pages(struct linux_binprm *bprm, bprm->loader -= stack_shift; bprm->exec -= stack_shift; - if (mmap_write_lock_killable(mm)) - return -EINTR; - vm_flags = VM_STACK_FLAGS; /* @@ -807,7 +792,7 @@ int setup_arg_pages(struct linux_binprm *bprm, ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end, vm_flags); if (ret) - goto out_unlock; + return ret; BUG_ON(prev != vma); if (unlikely(vm_flags & VM_EXEC)) { @@ -819,7 +804,7 @@ int setup_arg_pages(struct linux_binprm *bprm, if (stack_shift) { ret = shift_arg_pages(vma, stack_shift); if (ret) - goto out_unlock; + return ret; } /* mprotect_fixup is overkill to remove the temporary stack flags */ @@ -846,11 +831,17 @@ int setup_arg_pages(struct linux_binprm *bprm, current->mm->start_stack = bprm->p; ret = expand_stack(vma, stack_base); if (ret) - ret = -EFAULT; + return -EFAULT; -out_unlock: + /* + * From this point on, anything that wants to poke around in the + * mm_struct must lock it by itself. + */ + bprm->vma = NULL; mmap_write_unlock(mm); - return ret; + mmput(mm); + bprm->mm = NULL; + return 0; } EXPORT_SYMBOL(setup_arg_pages); @@ -1114,8 +1105,6 @@ 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 @@ -1127,11 +1116,12 @@ 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; } } + /* bprm->mm stays refcounted, current->mm takes an extra reference */ + mmget(mm); task_lock(tsk); active_mm = tsk->active_mm; membarrier_exec_mmap(mm); @@ -1141,7 +1131,6 @@ 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); @@ -1397,8 +1386,6 @@ int begin_new_exec(struct linux_binprm * bprm) if (retval) goto out; - bprm->mm = NULL; - #ifdef CONFIG_POSIX_TIMERS exit_itimers(me->signal); flush_itimer_signals(); @@ -1545,6 +1532,18 @@ void setup_new_exec(struct linux_binprm * bprm) me->mm->task_size = TASK_SIZE; mutex_unlock(&me->signal->exec_update_mutex); mutex_unlock(&me->signal->cred_guard_mutex); + +#ifndef CONFIG_MMU + /* + * On MMU, setup_arg_pages() wants to access bprm->vma after this point, + * so we can't drop the mmap lock yet. + * On !MMU, we have neither setup_arg_pages() nor bprm->vma, so we + * should drop the lock here. + */ + mmap_write_unlock(bprm->mm); + mmput(bprm->mm); + bprm->mm = NULL; +#endif } EXPORT_SYMBOL(setup_new_exec); @@ -1581,6 +1580,7 @@ static void free_bprm(struct linux_binprm *bprm) { if (bprm->mm) { acct_arg_size(bprm, 0); + mmap_write_unlock(bprm->mm); mmput(bprm->mm); } free_arg_pages(bprm); diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 0571701ab1c5..3bf06212fbae 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -22,7 +22,7 @@ struct linux_binprm { # define MAX_ARG_PAGES 32 struct page *page[MAX_ARG_PAGES]; #endif - struct mm_struct *mm; + struct mm_struct *mm; /* nascent mm, write-locked */ unsigned long p; /* current top of mem */ unsigned long argmin; /* rlimit marker for copy_strings() */ unsigned int -- 2.28.0.806.g8561365e88-goog