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 29C2118E76B for ; Fri, 18 Oct 2024 08:47:20 +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=1729241241; cv=none; b=qdD0filJFxuadtXhDgCXkLqa0QuWR+b1D0WToE5TCl6WiOFc2QrB4W/lCaJZOGHqtpLs2pLU+gTq8pqtzADnY3dJnMIpiNtRvZlReUFStJbSkGlSFkT4Xacjjshukhn0LKsq+mf0Uru0geModJISahHEKxA3YURGpx62S6+1nwU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729241241; c=relaxed/simple; bh=fQeb01CaKI5jdhIpCvwWzDL/PMMLZyYp4syorKQpjfU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VAzUH3ml/R9bUftwM2RhQwrElCKf3fJmb1xwmIeMyOVMf5xKTKCyNEWdfGX8Cqj3X1MVF4gE20QXzEiWJpLikCX+3RvYRa6NhA1HlMhh+yfPIKXbx168xNugrjawZRZQM8O+LZN9wmA2sWCuM6PuFDSzHvVauwq10/WxTdPilq4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kgZ0Pny4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="kgZ0Pny4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81759C4CEC3; Fri, 18 Oct 2024 08:47:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1729241240; bh=fQeb01CaKI5jdhIpCvwWzDL/PMMLZyYp4syorKQpjfU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kgZ0Pny4HdNf86e62RL4uom3yOHqaK2hQxuksFRta1pDyA/Jv1+WFYnyYK5w+0wgi OA+NtXJdGQ5GsyyYEZccFgVAO+ZdJYJD81imxHl3pF/bgKsZ/JrJ7RJwgIYnOckz/w nxttjp7N2LsaUcGpcNFeWY6k/j9txkPvqb3D6dNM= Date: Fri, 18 Oct 2024 10:47:13 +0200 From: Greg KH To: Mike Rapoport Cc: stable@vger.kernel.org, Patrick Roy Subject: Re: [PATCH 5.15.y] secretmem: disable memfd_secret() if arch cannot set direct map Message-ID: <2024101853-margin-clumsily-6239@gregkh> References: <2024101412-prowling-snowflake-9fe0@gregkh> <20241014152103.1328260-1-rppt@kernel.org> <2024101410-jiffy-handsaw-43e3@gregkh> Precedence: bulk X-Mailing-List: stable@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: On Mon, Oct 14, 2024 at 07:35:03PM +0300, Mike Rapoport wrote: > On Mon, Oct 14, 2024 at 05:55:22PM +0200, Greg KH wrote: > > On Mon, Oct 14, 2024 at 06:21:03PM +0300, Mike Rapoport wrote: > > > From: Patrick Roy > > > > > > Return -ENOSYS from memfd_secret() syscall if !can_set_direct_map(). > > > This is the case for example on some arm64 configurations, where marking > > > 4k PTEs in the direct map not present can only be done if the direct map > > > is set up at 4k granularity in the first place (as ARM's > > > break-before-make semantics do not easily allow breaking apart > > > large/gigantic pages). > > > > > > More precisely, on arm64 systems with !can_set_direct_map(), > > > set_direct_map_invalid_noflush() is a no-op, however it returns success > > > (0) instead of an error. This means that memfd_secret will seemingly > > > "work" (e.g. syscall succeeds, you can mmap the fd and fault in pages), > > > but it does not actually achieve its goal of removing its memory from > > > the direct map. > > > > > > Note that with this patch, memfd_secret() will start erroring on systems > > > where can_set_direct_map() returns false (arm64 with > > > CONFIG_RODATA_FULL_DEFAULT_ENABLED=n, CONFIG_DEBUG_PAGEALLOC=n and > > > CONFIG_KFENCE=n), but that still seems better than the current silent > > > failure. Since CONFIG_RODATA_FULL_DEFAULT_ENABLED defaults to 'y', most > > > arm64 systems actually have a working memfd_secret() and aren't be > > > affected. > > > > > > >>From going through the iterations of the original memfd_secret patch > > > series, it seems that disabling the syscall in these scenarios was the > > > intended behavior [1] (preferred over having > > > set_direct_map_invalid_noflush return an error as that would result in > > > SIGBUSes at page-fault time), however the check for it got dropped > > > between v16 [2] and v17 [3], when secretmem moved away from CMA > > > allocations. > > > > > > [1]: https://lore.kernel.org/lkml/20201124164930.GK8537@kernel.org/ > > > [2]: https://lore.kernel.org/lkml/20210121122723.3446-11-rppt@kernel.org/#t > > > [3]: https://lore.kernel.org/lkml/20201125092208.12544-10-rppt@kernel.org/ > > > > > > Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas") > > > Signed-off-by: Patrick Roy > > > Reviewed-by: Mike Rapoport (Microsoft) > > > Signed-off-by: Mike Rapoport (Microsoft) > > > --- > > > mm/secretmem.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > What is the git id of this change in Linus's tree? > > 532b53cebe58f34ce1c0f34d866f5c0e335c53c6 Thanks, next time please include that in the original patch so we don't have to do this back/forth emails :) now queued up. greg k-h