From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [RFC PATCH 3/5] mm: introduce VM_EXEC_KEEP Date: Tue, 28 Jul 2020 08:38:58 -0500 Message-ID: <87365bg3nx.fsf@x220.int.ebiederm.org> References: <1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com> <1595869887-23307-4-git-send-email-anthony.yznaga@oracle.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from out03.mta.xmission.com ([166.70.13.233]:48638 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730069AbgG1NmN (ORCPT ); Tue, 28 Jul 2020 09:42:13 -0400 In-Reply-To: <1595869887-23307-4-git-send-email-anthony.yznaga@oracle.com> (Anthony Yznaga's message of "Mon, 27 Jul 2020 10:11:25 -0700") Sender: linux-arch-owner@vger.kernel.org List-ID: To: Anthony Yznaga Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, mhocko@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, arnd@arndb.de, keescook@chromium.org, gerg@linux-m68k.org, ktkhai@virtuozzo.com, christian.brauner@ubuntu.com, peterz@infradead.org, esyr@redhat.com, jgg@ziepe.ca, christian@kellner.me, areber@redhat.com, cyphar@cyphar.com, steven.sistare@oracle.com Anthony Yznaga writes: > A vma with the VM_EXEC_KEEP flag is preserved across exec. For anonymous > vmas only. For safety, overlap with fixed address VMAs created in the new > mm during exec (e.g. the stack and elf load segments) is not permitted and > will cause the exec to fail. > (We are studying how to guarantee there are no conflicts. Comments welcome.) > > diff --git a/fs/exec.c b/fs/exec.c > index 262112e5f9f8..1de09c4eef00 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1069,6 +1069,20 @@ ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len) > EXPORT_SYMBOL(read_code); > #endif > > +static int vma_dup_some(struct mm_struct *old_mm, struct mm_struct *new_mm) > +{ > + struct vm_area_struct *vma; > + int ret; > + > + for (vma = old_mm->mmap; vma; vma = vma->vm_next) > + if (vma->vm_flags & VM_EXEC_KEEP) { > + ret = vma_dup(vma, new_mm); > + if (ret) > + return ret; > + } > + return 0; > +} > + > /* > * Maps the mm_struct mm into the current task struct. > * On success, this function returns with the mutex > @@ -1104,6 +1118,12 @@ static int exec_mmap(struct mm_struct *mm) > mutex_unlock(&tsk->signal->exec_update_mutex); > return -EINTR; > } > + ret = vma_dup_some(old_mm, mm); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ouch! An unconditional loop through all of the vmas of the execing process, just in case there is a VM_EXEC_KEEP vma. I know we already walk the list in exit_mmap, but I get the feeling this will slow exec down when this feature is not enabled, especially when a process with a lot of vmas is calling exec. > + if (ret) { > + mmap_read_unlock(old_mm); > + mutex_unlock(&tsk->signal->exec_update_mutex); > + return ret; > + } > } > > task_lock(tsk);