linux-kernel - Re: [PATCH v3] module: add in-kernel support for decompressing

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Message-ID: <YbPnCo8ZZ6vrMASe@google.com>
Date:   Fri, 10 Dec 2021 15:47:22 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Jessica Yu <jeyu@...nel.org>, Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] module: add in-kernel support for decompressing

On Fri, Dec 10, 2021 at 03:35:30PM -0800, Luis Chamberlain wrote:
> On Fri, Dec 10, 2021 at 03:21:03PM -0800, Dmitry Torokhov wrote:
> > On Fri, Dec 10, 2021 at 02:05:17PM -0800, Luis Chamberlain wrote:
> > > On Thu, Dec 09, 2021 at 10:09:17PM -0800, Dmitry Torokhov wrote:
> > > > +static ssize_t module_xz_decompress(struct load_info *info,
> > > > +				    const void *buf, size_t size)
> > > > +{
> > > > +	static const u8 signature[] = { 0xfd, '7', 'z', 'X', 'Z', 0 };
> > > > +	struct xz_dec *xz_dec;
> > > > +	struct xz_buf xz_buf;
> > > > +	enum xz_ret xz_ret;
> > > > +	size_t new_size = 0;
> > > > +	ssize_t retval;
> > > > +
> > > > +	if (size < sizeof(signature) ||
> > > > +	    memcmp(buf, signature, sizeof(signature))) {
> > > > +		pr_err("not an xz compressed module\n");
> > > > +		return -EINVAL;
> > > > +	}
> > > > +
> > > > +	xz_dec = xz_dec_init(XZ_DYNALLOC, (u32)-1);
> > > > +	if (!xz_dec)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	xz_buf.in_size = size;
> > > > +	xz_buf.in = buf;
> > > > +	xz_buf.in_pos = 0;
> > > > +
> > > > +	do {
> > > > +		struct page *page = module_get_next_page(info);
> > > > +		if (!page) {
> > > > +			retval = -ENOMEM;
> > > > +			goto out;
> > > > +		}
> > > 
> > > This looks very similar to fw_decompress_xz_pages() on
> > > drivers/base/firmware_loader/main.c
> > > 
> > > Is there any sharing possible with decompression between the two?
> > 
> > Ideally we'd get proper crypto API allowing this (page by page)
> > decompression and then we can switch to it in both places and stop
> > calling into particular algorithms directly. Unfortunately this is not
> > something I can sign up for at this time.
> > 
> > As it is I am not sure if it worth to try to split out XZ code and share
> > it between module and firmware loader.
> 
> Got it, makes sense.
> 
> What type of tests have you implemented for this ? kmod has quite a bit
> of tests. Can you add some for this?

OK, will do.

Thanks.

-- 
Dmitry