Re: [PATCH v3 1/6] hw/sd/sdcard: Fix size check for backing block image

[Warner Losh <imp@bsdimp.com>]

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On Tue, Sep 9, 2025 at 6:51 AM Jan Kiszka <jan.kiszka@siemens.com> wrote:

> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> Alignment rules apply the the individual partitions (user, boot, later
> on also RPMB) and depend both on the size of the image and the type of
> the device. Up to and including 2GB, the power-of-2 rule applies to the
> user data area. For larger images, multiples of 512 sectors must be used
> for eMMC and multiples of 512K for SD-cards. Fix the check accordingly
> and also detect if the image is too small to even hold the boot
> partitions.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> CC: Warner Losh <imp@bsdimp.com>
> CC: Cédric Le Goater <clg@kaod.org>
> CC: Joel Stanley <joel@jms.id.au>
> CC: Alistair Francis <alistair@alistair23.me>
> CC: Alexander Bulekov <alxndr@bu.edu>
> ---
>  hw/sd/sd.c | 61 +++++++++++++++++++++++++++++++++++++-----------------
>

Reviewed-by: Warner Losh <imp@bsdimp.com>



>  1 file changed, 42 insertions(+), 19 deletions(-)
> diff --git a/hw/sd/sd.c b/hw/sd/sd.c
> index d7a496d77c..b42cd01d1f 100644
> --- a/hw/sd/sd.c
> +++ b/hw/sd/sd.c
> @@ -2759,6 +2759,28 @@ static void sd_instance_finalize(Object *obj)
>      timer_free(sd->ocr_power_timer);
>  }
>
> +static void sd_blk_size_error(SDState *sd, int64_t blk_size,
> +                              int64_t blk_size_aligned, const char *rule,
> +                              Error **errp)
> +{
> +    const char *dev_type = sd_is_emmc(sd) ? "eMMC" : "SD card";
> +    char *blk_size_str;
> +
> +    blk_size_str = size_to_str(blk_size);
> +    error_setg(errp, "Invalid %s size: %s", dev_type, blk_size_str);
> +    g_free(blk_size_str);
> +
> +    blk_size_str = size_to_str(blk_size_aligned);
> +    error_append_hint(errp,
> +                      "%s size has to be %s, e.g. %s.\n"
> +                      "You can resize disk images with"
> +                      " 'qemu-img resize <imagefile> <new-size>'\n"
> +                      "(note that this will lose data if you make the"
> +                      " image smaller than it currently is).\n",
> +                      dev_type, rule, blk_size_str);
> +    g_free(blk_size_str);
> +}
> +
>  static void sd_realize(DeviceState *dev, Error **errp)
>  {
>      SDState *sd = SDMMC_COMMON(dev);
> @@ -2781,25 +2803,26 @@ static void sd_realize(DeviceState *dev, Error
> **errp)
>              return;
>          }
>
> -        blk_size = blk_getlength(sd->blk);
> -        if (blk_size > 0 && !is_power_of_2(blk_size)) {
> -            int64_t blk_size_aligned = pow2ceil(blk_size);
> -            char *blk_size_str;
> -
> -            blk_size_str = size_to_str(blk_size);
> -            error_setg(errp, "Invalid SD card size: %s", blk_size_str);
> -            g_free(blk_size_str);
> -
> -            blk_size_str = size_to_str(blk_size_aligned);
> -            error_append_hint(errp,
> -                              "SD card size has to be a power of 2, e.g.
> %s.\n"
> -                              "You can resize disk images with"
> -                              " 'qemu-img resize <imagefile>
> <new-size>'\n"
> -                              "(note that this will lose data if you make
> the"
> -                              " image smaller than it currently is).\n",
> -                              blk_size_str);
> -            g_free(blk_size_str);
> -
> +        blk_size = blk_getlength(sd->blk) - sd->boot_part_size * 2;
> +        if (blk_size > SDSC_MAX_CAPACITY) {
> +            if (sd_is_emmc(sd) && blk_size % (1 << HWBLOCK_SHIFT) != 0) {
> +                int64_t blk_size_aligned =
> +                    ((blk_size >> HWBLOCK_SHIFT) + 1) << HWBLOCK_SHIFT;
> +                sd_blk_size_error(sd, blk_size, blk_size_aligned,
> +                                  "multiples of 512", errp);
> +                return;
> +            } else if (!sd_is_emmc(sd) && blk_size % (512 * KiB)) {
> +                int64_t blk_size_aligned = ((blk_size >> 19) + 1) << 19;
> +                sd_blk_size_error(sd, blk_size, blk_size_aligned,
> +                                  "multiples of 512K", errp);
> +                return;
> +            }
> +        } else if (blk_size > 0 && !is_power_of_2(blk_size)) {
> +            sd_blk_size_error(sd, blk_size, pow2ceil(blk_size), "a power
> of 2",
> +                              errp);
> +            return;
> +        } else if (blk_size < 0) {
> +            error_setg(errp, "eMMC image smaller than boot partitions");
>              return;
>          }
>
> --
> 2.51.0
>
>

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