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 730BE1AC887 for ; Mon, 14 Oct 2024 15:21:14 +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=1728919274; cv=none; b=MkYB0NJU+jgTpJmoRz5x9X6HZYcdyRRrp9Om5n7iJafhAhpirLveyFyLfig6dG8y6xXaHfzeUILrtaat4Dt/oErxBJAvyL+g86jRBKtoqoeiofaikKAsBDZk5vvpNKZbIi29y78qw91IQDNsmmtANzmRenf9zpRl5ng3+vnzFwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728919274; c=relaxed/simple; bh=vfyV2JLArq//R3EZAY5T/9gykyXsGDAtc1ey8X9Ha9I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bt4Bzays11pJDvTOJ+ZsL9nGC8SbYIu1MGdeRIgU2tSnYC4APMlL4hXDnn+O1E/JQeFy1kSGDDFg9QLlI+kU/Gb5B3SLJt0CuG8aZxLSViYB43/koltYpb4QnJ0NyuMsTj+gSN2LH867CDxgeaKPMrM+QUiMFHOCTSGscRpBvHI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=D9hdYh6t; 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="D9hdYh6t" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 262A8C4CEC3; Mon, 14 Oct 2024 15:21:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728919274; bh=vfyV2JLArq//R3EZAY5T/9gykyXsGDAtc1ey8X9Ha9I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=D9hdYh6tIv2YYru2QRnQcCc+G9LQD89PUvfPXnvxlC0nsxEOL1+6+Qw1dUgYfHlNR 12Ghy8D4g89gdjH8HzGDYv7xF9w63t+nTooCQ6J9Ug6sAjX+3tn60CQ2WH7Rv+b9Oc qNLPopQd0vqd3qiNUsUrqcGNsYxghTnGe1gz0bi7sKVORLUGrqAz+ynrUezucXqvsb 6XwZnJdIfHqvHyoqJGklrx+lwgSpxDN8E/SyM6ey6PVDA1o1Nb+eJ/KcOUsg0Zz6JQ dJGe5Xzrz0BjnI+D8FXPtc4xH8vw9RFjNg4FYURdCerwGjvPTc54o+BthAtJs3suZk YmldPonncf1uQ== From: Mike Rapoport To: stable@vger.kernel.org Cc: Mike Rapoport , Patrick Roy Subject: [PATCH 5.15.y] secretmem: disable memfd_secret() if arch cannot set direct map Date: Mon, 14 Oct 2024 18:21:03 +0300 Message-ID: <20241014152103.1328260-1-rppt@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <2024101412-prowling-snowflake-9fe0@gregkh> References: <2024101412-prowling-snowflake-9fe0@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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(-) diff --git a/mm/secretmem.c b/mm/secretmem.c index d1986ce2e7c7..624663a94808 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -234,7 +234,7 @@ SYSCALL_DEFINE1(memfd_secret, unsigned int, flags) /* make sure local flags do not confict with global fcntl.h */ BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC); - if (!secretmem_enable) + if (!secretmem_enable || !can_set_direct_map()) return -ENOSYS; if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC)) @@ -278,7 +278,7 @@ static int secretmem_init(void) { int ret = 0; - if (!secretmem_enable) + if (!secretmem_enable || !can_set_direct_map()) return ret; secretmem_mnt = kern_mount(&secretmem_fs); -- 2.43.0