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Re: [Qemu-devel] [RFC] memory-backend-file/nvdimm: support read-only fil
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Qemu-devel] [RFC] memory-backend-file/nvdimm: support read-only files as memory-backends |
Date: |
Tue, 9 Jul 2019 12:53:45 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 |
Cc'ing Igor & Xiao.
On 7/8/19 11:19 PM, Julio Montes wrote:
> Currently is not possible to use a file that is part of a read-only
> filesystem as memory backend for nvdimm devices, even if this is not modified
> in the guest. In order to improve the security of Virtual Machines that share
> and do not modify the memory-backend-file, QEMU should support
> read-only memory-backeds.
>
> Use case:
> * Kata Containers use a memory-backed-file as read-only rootfs, and this
> file is used to start all the virtual machines in the node.
> It would be really bad if somehow a malicious container modified it.
>
> Signed-off-by: Julio Montes <address@hidden>
> ---
> exec.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/exec.c b/exec.c
> index 50ea9c5aaa..1eb170b55a 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1852,6 +1852,12 @@ static int file_ram_open(const char *path,
> break;
> }
> g_free(filename);
> + } else if (errno == EROFS) {
> + fd = open(path, O_RDONLY);
While I can understand your use case, I'm not sure we want this silenced
as default. I'd expect an explicit command line option for that backend,
but I don't know well this area so let's wait for other to review.
> + if (fd >= 0) {
> + /* @path names an existing read-only file, use it */
> + break;
> + }
> }
> if (errno != EEXIST && errno != EINTR) {
> error_setg_errno(errp, errno,
> --
> 2.17.2
>