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 20B7A231C92 for ; Mon, 14 Oct 2024 16:38:37 +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=1728923918; cv=none; b=ty09q6F0Aj4gTQxFU4qhef7VLZhV0jrzWJfHMZqXDZhXO71BHRpv6d3KtWZdN1ZCs47/wWrh8fwJXYsAPqWceyoGYSSTJ4oRIxMrAC3n53Z/k3prq31DyY+gQCQTRqwWzcc4ILOb0QNZ8DwonEFa32FDJuIlhRIPZjdxUc9+v2Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728923918; c=relaxed/simple; bh=yyU3R7qUtKGClEduDT1qq4PwhvXLOOsu89t//ztsvwU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QTlFeYaJnfydRobX6asu5AHkCKjfbjaI67wemRoFHFwEfCOaKPxFRVpqQLQFHCkxRh1UefuiOcJC77RCNKmnF/EKJB3Wa4M1M770oY7yYcrfOlkwFRkXnGXqBGNurAWKsshWopW/e7HnHYX8lNqwS3iA2oW7/HMZKahInGDXXy8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lkEysTOm; 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="lkEysTOm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5BA4CC4CEC3; Mon, 14 Oct 2024 16:38:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728923917; bh=yyU3R7qUtKGClEduDT1qq4PwhvXLOOsu89t//ztsvwU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lkEysTOmKBHKGl2m0eRraANuQ5Eh54H/XjBwbRpZONmslvoLpZuXSA58WHN4yCiI0 ypYpb5YdDrDACcpS3mEIEGQaTO7M0MnJGRLHoDLmN4Y7pNII6I+t81uvI5mdkCamDV YftfAWCqyHDixHbJbqxTRHaQFhBrjcPbeefIkn1jLGw0au3IzpI5qfL+V913pczZ2I vOhT7AvStItIFzHvVVJecMIAtEvknToHk4ExdJqOQTb+LYsaCU/3pso9ol7ZPpSyNU yDfTH9xc+q2K5wcVdktZdU72Fx2kWmjaEbpYUve7eprAd/HbKeBlmSGmw18qIKNMPR koylfjWFqfhrg== Date: Mon, 14 Oct 2024 19:35:03 +0300 From: Mike Rapoport To: Greg KH 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: 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: <2024101410-jiffy-handsaw-43e3@gregkh> 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 -- Sincerely yours, Mike.