From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D1EF539023C; Thu, 9 Apr 2026 15:13:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775747605; cv=none; b=lIgdtjl/4dcY7xQBU6U5PpyzFapN6JMpGswbXcI5KlqwJ4POXTQ7dFQBxqdNm36GrMxmqDaE+h8PgNsWkKKN5HOqjLPbxfNDZvKdEAXk3v5FxItpzDMWNjAuXLtmfCW6wLnomHVBNGJHAvHmhet0ipdvm7bMMH7hpdVPrDi7a1g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775747605; c=relaxed/simple; bh=owesWMMhEZ10jRbXPNEnxMG0zX+QmTfFOcYuaS6Uh0o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=b7OZHjPTSXqE6oqnPC12DsG2FrrVc7lScgy+Nf4aY2nEZufVyvL1+foIwxZnorMV+LpGIvdXmURCYEwAUK4r2sDd/XNQxMeM+XVoR2ivnEeCa8wzRfDqhOT4LTCewW1ivMyZn21JVHwVCCGDKvsotbqet54FyqMTXrBmz2AT6Ck= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=l4EN9yu5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="l4EN9yu5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E6ECCC116C6; Thu, 9 Apr 2026 15:13:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775747605; bh=owesWMMhEZ10jRbXPNEnxMG0zX+QmTfFOcYuaS6Uh0o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=l4EN9yu524R4fMKtvtcTuJmGimqWFPvuyMWu5Y+SlnHXdSp+SHpy8AtM2EXrf1522 rXrnFY8/E5aAHwDVA0tlaQk+rsUzOydQolkX2P8gn+nAHCetUtkzB2mxwLJ2dWaej/ SevoiQOBFet5p4dBRVg3GCjZ8t6KTwvFLfgV8O48llfr3A3yO2Kz+JlIzNhP0uDSw4 mtdrfqI8M/fsL/wa33uQffEvI2UxZtt2/8BOTJeLX2Tt6fimxeCAfaS+gAhC71N6EF ZUcN9x87gzSTFDol4yR+vKH1kft72K1FWXfiSoOlNpzr310/3F5quZSDr++OwnN+2M u5BEbnaY47OpA== Date: Thu, 9 Apr 2026 18:13:17 +0300 From: Mike Rapoport To: "Denis M. Karpov" Cc: harry@kernel.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, peterx@redhat.com, pfalcato@suse.de, brauner@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, usama.arif@linux.dev Subject: Re: [PATCH v2] userfaultfd: allow registration of ranges below mmap_min_addr Message-ID: References: <20260409103345.15044-1-komlomal@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260409103345.15044-1-komlomal@gmail.com> On Thu, Apr 09, 2026 at 01:33:45PM +0300, Denis M. Karpov wrote: > The current implementation of validate_range() in fs/userfaultfd.c > performs a hard check against mmap_min_addr. This is redundant because > UFFDIO_REGISTER operates on memory ranges that must already be backed > by a VMA. > > Enforcing mmap_min_addr or capability checks again in userfaultfd is > unnecessary and prevents applications like binary compilers from > using UFFD for valid memory regions mapped by application. > > Remove the redundant check for mmap_min_addr. > > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") > Signed-off-by: Denis M. Karpov Reviewed-by: Mike Rapoport (Microsoft) > --- > v2: > - Remove the check entirely rather than replacing it, as suggested by > Harry Yoo and Lorenzo Stoakes. > - Added Fixes tag. > - Link to v1: https://lore.kernel.org/r/20260407081442.6256-1-komlomal@gmail.com > --- > fs/userfaultfd.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index bdc84e521..4b53dc4a3 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1238,8 +1238,6 @@ static __always_inline int validate_unaligned_range( > return -EINVAL; > if (!len) > return -EINVAL; > - if (start < mmap_min_addr) > - return -EINVAL; > if (start >= task_size) > return -EINVAL; > if (len > task_size - start) > -- > 2.43.0 > -- Sincerely yours, Mike.