linux-kernel - Re: [PATCH v7 2/8] efi: Add embedded peripheral firmware support

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Date:   Fri, 11 Oct 2019 14:48:34 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Jonathan Corbet <corbet@....net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Peter Jones <pjones@...hat.com>,
        Dave Olsthoorn <dave@...aar.me>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-input@...r.kernel.org
Subject: Re: [PATCH v7 2/8] efi: Add embedded peripheral firmware support

On Fri, Oct 04, 2019 at 04:50:50PM +0200, Hans de Goede wrote:
> +static int __init efi_check_md_for_embedded_firmware(
> +	efi_memory_desc_t *md, const struct efi_embedded_fw_desc *desc)
> +{
> +	const u64 prefix = *((u64 *)desc->prefix);
> +	struct sha256_state sctx;
> +	struct embedded_fw *fw;
> +	u8 sha256[32];
> +	u64 i, size;
> +	void *map;
> +
> +	size = md->num_pages << EFI_PAGE_SHIFT;
> +	map = memremap(md->phys_addr, size, MEMREMAP_WB);

Since our limitaiton is the init process must have mostly finished,
it implies early x86 boot code cannot use this, what measures can we
take to prevent / check for such conditions to be detected and
gracefully errored out?

> +	if (!map) {
> +		pr_err("Error mapping EFI mem at %#llx\n", md->phys_addr);
> +		return -ENOMEM;
> +	}
> +
> +	size -= desc->length;

Remind me again, why we decrement the size here?
I was going to ask if we didn't need a:

if (desc->length > size) {
	memunmap(map);
	return -EINVAL;
}

> +	for (i = 0; i < size; i += 8) {
> +		u64 *mem = map + i;
> +
> +		if (*mem != prefix)
> +			continue;
> +
> +		sha256_init(&sctx);
> +		sha256_update(&sctx, map + i, desc->length);
> +		sha256_final(&sctx, sha256);
> +		if (memcmp(sha256, desc->sha256, 32) == 0)
> +			break;
> +	}
> +	if (i >= size) {
> +		memunmap(map);
> +		return -ENOENT;
> +	}
> +
> +	pr_info("Found EFI embedded fw '%s'\n", desc->name);

Otherwise looks good.

  Luis