linux-kernel - Re: [PATCH v5 6/6] soc/tegra: Expose Boot Configuration Table via sysfs

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Date:   Mon, 18 May 2020 09:45:57 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        David Heidelberg <david@...t.cz>,
        Peter Geis <pgwipeout@...il.com>,
        Stephen Warren <swarren@...dotorg.org>,
        Nicolas Chauvet <kwizart@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Billy Laws <blaws05@...il.com>,
        Nils Östlund <nils@...tan.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-tegra@...r.kernel.org, linux-block@...r.kernel.org,
        Andrey Danin <danindrey@...l.ru>,
        Gilles Grandou <gilles@...ndou.net>,
        Ryan Grachek <ryan@...ted.us>, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Steve McIntyre <steve@...val.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v5 6/6] soc/tegra: Expose Boot Configuration Table via
 sysfs

On Sat, May 16, 2020 at 06:36:44PM +0300, Dmitry Osipenko wrote:
> It's quite useful to have unencrypted BCT exposed to userspace for
> debugging purposes, so let's expose it via sysfs.  The BCT data will be
> present in '/sys/tegra/boot_config_table' binary file if BCT is available.
[...]
> +/*
> + * spare_bct[] will be released once kernel is booted, hence not wasting
> + * kernel space if BCT is missing. The tegra_bct can't be allocated during
> + * of BCT setting up because it's too early for the slab allocator.
> + */
> +static u8 spare_bct[SZ_8K] __initdata;
> +static u8 *tegra_bct;
> +
> +static ssize_t boot_config_table_read(struct file *filp,
> +				      struct kobject *kobj,
> +				      struct bin_attribute *bin_attr,
> +				      char *buf, loff_t off, size_t count)
> +{
> +	memcpy(buf, tegra_bct + off, count);
> +	return count;
> +}
> +static BIN_ATTR_RO(boot_config_table, 0);
> +
> +static int __init tegra_bootdata_bct_sysfs_init(void)
> +{
> +	if (!bin_attr_boot_config_table.size)
> +		return 0;
> +
> +	tegra_bct = kmalloc(GFP_KERNEL, bin_attr_boot_config_table.size);
> +	if (!tegra_bct)
> +		return -ENOMEM;
> +
> +	memcpy(tegra_bct, spare_bct, bin_attr_boot_config_table.size);
> +
> +	return sysfs_create_bin_file(tegra_soc_kobj,
> +				     &bin_attr_boot_config_table);

Should we consider freeing the table if sysfs registration fails?

> +}
> +late_initcall(tegra_bootdata_bct_sysfs_init)
> +
> +void __init tegra_bootdata_bct_setup(void __iomem *bct_ptr, size_t bct_size)
> +{
> +	memcpy_fromio(spare_bct, bct_ptr, bct_size);
> +	bin_attr_boot_config_table.size = bct_size;
[...]

The size isn't checked anywhere. How the maximum is obtained? At least
a comment would be good if the 8k limit is guaranteed by other means.

Best Regards,
Michał Mirosław