target/linux/ipq806x/patches-6.1/901-01-ARM-decompressor-support-memory-start-validation-.patch

   1 From 2f86b9b71a11f86e3d850214ab781ebb17d7260e Mon Sep 17 00:00:00 2001
   2 From: Christian Marangi <ansuelsmth@gmail.com>
   3 Date: Fri, 19 Jan 2024 19:48:30 +0100
   4 Subject: [PATCH v2 1/2] ARM: decompressor: support memory start validation for
   5  appended DTB
   6
   7 There is currently a problem with a very specific sets of kernel config
   8 and AUTO_ZRELADDR.
   9
  10 For the most common case AUTO_ZRELADDR check the PC register and
  11 calculate the start of the physical memory. Then fdt_check_mem_start is
  12 called to make sure the detected value makes sense by comparing it with
  13 what is present in DTB in the memory nodes and if additional fixup are
  14 required with the use of linux,usable-memory-range in the chosen node to
  15 hardcode usable memory range in case some reserved space needs to be
  16 addressed. With the help of this function the right address is
  17 calculated and the kernel correctly decompress and loads.
  18
  19 Things starts to become problematic when in the mix,
  20 CONFIG_ARM_APPENDED_DTB is used. This is a particular kernel config is
  21 used when legacy systems doesn't support passing a DTB directly and a
  22 DTB is appended at the end of the image.
  23
  24 In such case, fdt_check_mem_start is skipped in AUTO_ZRELADDR iteration
  25 as the appended DTB can be augumented later with ATAGS passed from the
  26 bootloader (if CONFIG_ARM_ATAG_DTB_COMPAT is enabled).
  27
  28 The main problem and what this patch address is the fact that
  29 fdt_check_mem_start is never called later when the appended DTB is
  30 augumented, hence any fixup and validation is not done making AUTO_ZRELADDR
  31 detection inconsistent and most of the time wrong.
  32
  33 Add support in head.S for this by checking if AUTO_ZRELADDR is enabled
  34 and calling fdt_check_mem_start with the appended DTB and the augumented
  35 values permitting legacy device to provide info in DTB instead of
  36 disabling AUTO_ZRELADDR and hardcoding the physical address offsets.
  37
  38 Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
  39 Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
  40 Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
  41 ---
  42  arch/arm/boot/compressed/head.S | 22 ++++++++++++++++++++++
  43  1 file changed, 22 insertions(+)
  44
  45 --- a/arch/arm/boot/compressed/head.S
  46 +++ b/arch/arm/boot/compressed/head.S
  47 @@ -443,6 +443,28 @@ restart:   adr     r0, LC1
  48                 add     r6, r6, r5
  49                 add     r10, r10, r5
  50                 add     sp, sp, r5
  51 +
  52 +#ifdef CONFIG_AUTO_ZRELADDR
  53 +               /*
  54 +                * Validate calculated start of physical memory with appended DTB.
  55 +                * In the first iteration for physical memory start calculation,
  56 +                * we skipped validating it as it could have been augumented by
  57 +                * ATAGS stored at an offset from the same start of physical memory.
  58 +                *
  59 +                * We now have parsed them and augumented the appended DTB if asked
  60 +                * so we can finally validate the start of physical memory.
  61 +                *
  62 +                * This is needed to apply additional fixup with
  63 +                * linux,usable-memory-range or to make sure AUTO_ZRELADDR detected
  64 +                * the correct value.
  65 +                */
  66 +               sub     r0, r4, #TEXT_OFFSET    @ revert to base address
  67 +               mov     r1, r8                  @ use appended DTB
  68 +               bl      fdt_check_mem_start
  69 +
  70 +               /* Determine final kernel image address. */
  71 +               add     r4, r0, #TEXT_OFFSET
  72 +#endif
  73  dtb_check_done:
  74  #endif
  75