linux-kernel - Re: [PATCH 1/2] ARM: decompressor: support memory start validation for appended DTB

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Date: Sat, 20 Jan 2024 12:15:20 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Russell King <linux@...linux.org.uk>, Arnd Bergmann <arnd@...db.de>, 
	Andrew Morton <akpm@...ux-foundation.org>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Jonathan Corbet <corbet@....net>, 
	Thomas Gleixner <tglx@...utronix.de>, Randy Dunlap <rdunlap@...radead.org>, 
	"Mike Rapoport (IBM)" <rppt@...nel.org>, Eric DeVolder <eric.devolder@...cle.com>, 
	Nathan Chancellor <nathan@...nel.org>, "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>, 
	Kees Cook <keescook@...omium.org>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...ainline.org>, Linus Walleij <linus.walleij@...aro.org>, 
	John Crispin <john@...ozen.org>
Subject: Re: [PATCH 1/2] ARM: decompressor: support memory start validation
 for appended DTB

On Fri, Jan 19, 2024 at 9:14 PM Christian Marangi <ansuelsmth@...ilcom> wrote:
> There is currently a problem with a very specific sets of kernel config
> and AUTO_ZRELADDR.
>
> For the most common case AUTO_ZRELADDR check the PC register and
> calculate the start of the physical memory. Then fdt_check_mem_start is
> called to make sure the detected value makes sense by comparing it with
> what is present in DTB in the memory nodes and if additional fixup are
> required with the use of linux,usable-memory-range in the chosen node to
> hardcode usable memory range in case some reserved space needs to be
> addressed. With the help of this function the right address is
> calculated and the kernel correctly decompress and loads.
>
> Things starts to become problematic when in the mix,
> CONFIG_ARM_APPENDED_DTB is used. This is a particular kernel config is
> used when legacy systems doesn't support passing a DTB directly and a
> DTB is appended at the end of the image.
>
> In such case, fdt_check_mem_start is skipped in AUTO_ZRELADDR iteration
> as the appended DTB can be augumented later with ATAGS passed from the
> bootloader (if CONFIG_ARM_ATAG_DTB_COMPAT is enabled).
>
> The main problem and what this patch address is the fact that
> fdt_check_mem_start is never called later when the appended DTB is
> augumented, hence any fixup and validation is not done making AUTO_ZRELADDR
> detection inconsistent and most of the time wrong.
>
> Add support in head.S for this by checking if AUTO_ZRELADDR is enabled
> and calling fdt_check_mem_start with the appended DTB and the augumented
> values permitting legacy device to provide info in DTB instead of
> disabling AUTO_ZRELADDR and hardcoding the physical address offsets.
>
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>

LGTM, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

I plan to give this a try (for regression testing) next week.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds