[PATCH] fdt: Fix fdt_pack_reg() on 64-bit platforms

[Heinrich Schuchardt]

On 3/30/24 01:55, Sam Protsenko wrote:
> When "memory" node is being processed in fdt_pack_reg() on ARM64
> platforms, an unaligned bus access might happen, which leads to
> "synchronous abort" CPU exception. Consider next dts example:
>
>      / {
>          #address-cells = <2>;
>          #size-cells = <1>;
>
>          memory at 80000000 {
>              device_type = "memory";
>              reg = <0x0 0x80000000 0x3ab00000>,
>                    <0x0 0xc0000000 0x40000000>,
>                    <0x8 0x80000000 0x80000000>;
>          };
>      };
>
> After fdt_pack_reg() reads the first addr/size entry from such memory
> node, the "p" pointer becomes 12 bytes shifted from its original value
> (8 bytes for two address cells + 4 bytes for one size cell). So now it's
> not 64-bit aligned, and an attempt to do 64-bit bus access to that
> address will cause an abort like this:
>
>      "Synchronous Abort" handler, esr 0x96000021, far 0xba235efc
>
> This issue was originally reported by David Virag [1] who observed it
> happening on Samsung Exynos7885 SoC (ARM64), and later the same issue
> was observed on Samsung Exynos850 (ARM64).
>
> Fix the issue by using put_unaligned_be64() helper, which takes care of
> possible unaligned 64-bit accesses. That solution was proposed by Simon
> Glass in the original thread [1].
>
> [1] https://lists.denx.de/pipermail/u-boot/2023-July/522074.html
>
> Fixes: 739a01ed8e02 ("fdt_support: fix an endian bug of fdt_fixup_memory_banks")
> Suggested-by: Simon Glass <sjg at google.com>
> Reported-by: David Virag <virag.david003 at gmail.com>
> Closes: https://lists.denx.de/pipermail/u-boot/2023-July/522074.html
> Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>

Reviewed-by: Heinrich Schuchardt <xypron.glpk at gmx.de>

> ---
>   boot/fdt_support.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> index 090d82ee80a5..9844c70be806 100644
> --- a/boot/fdt_support.c
> +++ b/boot/fdt_support.c
> @@ -17,6 +17,7 @@
>   #include <linux/ctype.h>
>   #include <linux/types.h>
>   #include <asm/global_data.h>
> +#include <asm/unaligned.h>
>   #include <linux/libfdt.h>
>   #include <fdt_support.h>
>   #include <exports.h>
> @@ -421,13 +422,13 @@ static int fdt_pack_reg(const void *fdt, void *buf, u64 *address, u64 *size,
>
>   	for (i = 0; i < n; i++) {
>   		if (address_cells == 2)
> -			*(fdt64_t *)p = cpu_to_fdt64(address[i]);
> +			put_unaligned_be64(address[i], p);
>   		else
>   			*(fdt32_t *)p = cpu_to_fdt32(address[i]);
>   		p += 4 * address_cells;
>
>   		if (size_cells == 2)
> -			*(fdt64_t *)p = cpu_to_fdt64(size[i]);
> +			put_unaligned_be64(size[i], p);
>   		else
>   			*(fdt32_t *)p = cpu_to_fdt32(size[i]);
>   		p += 4 * size_cells;