[qemu-xen staging] hw/sd/sdcard: Do not allow invalid SD card sizes

[patchbot@xxxxxxx]

commit a9bcedd15a5834ca9ae6c3a97933e85ac7edbd36
Author:     Philippe Mathieu-Daudé <f4bug@xxxxxxxxx>
AuthorDate: Tue Jul 7 13:02:34 2020 +0200
Commit:     Philippe Mathieu-Daudé <f4bug@xxxxxxxxx>
CommitDate: Tue Jul 14 15:46:07 2020 +0200

    hw/sd/sdcard: Do not allow invalid SD card sizes
    
    QEMU allows to create SD card with unrealistic sizes. This could
    work, but some guests (at least Linux) consider sizes that are not
    a power of 2 as a firmware bug and fix the card size to the next
    power of 2.
    
    While the possibility to use small SD card images has been seen as
    a feature, it became a bug with CVE-2020-13253, where the guest is
    able to do OOB read/write accesses past the image size end.
    
    In a pair of commits we will fix CVE-2020-13253 as:
    
        Read command is rejected if BLOCK_LEN_ERROR or ADDRESS_ERROR
        occurred and no data transfer is performed.
    
        Write command is rejected if BLOCK_LEN_ERROR or ADDRESS_ERROR
        occurred and no data transfer is performed.
    
        WP_VIOLATION errors are not modified: the error bit is set, we
        stay in receive-data state, wait for a stop command. All further
        data transfer is ignored. See the check on sd->card_status at the
        beginning of sd_read_data() and sd_write_data().
    
    While this is the correct behavior, in case QEMU create smaller SD
    cards, guests still try to access past the image size end, and QEMU
    considers this is an invalid address, thus "all further data transfer
    is ignored". This is wrong and make the guest looping until
    eventually timeouts.
    
    Fix by not allowing invalid SD card sizes (suggesting the expected
    size as a hint):
    
      $ qemu-system-arm -M orangepi-pc -drive file=rootfs.ext2,if=sd,format=raw
      qemu-system-arm: Invalid SD card size: 60 MiB
      SD card size has to be a power of 2, e.g. 64 MiB.
      You can resize disk images with 'qemu-img resize <imagefile> <new-size>'
      (note that this will lose data if you make the image smaller than it 
currently is).
    
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Philippe Mathieu-Daudé <f4bug@xxxxxxxxx>
    Reviewed-by: Alistair Francis <alistair.francis@xxxxxxx>
    Reviewed-by: Peter Maydell <peter.maydell@xxxxxxxxxx>
    Message-Id: <20200713183209.26308-8-f4bug@xxxxxxxxx>
---
 hw/sd/sd.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/hw/sd/sd.c b/hw/sd/sd.c
index edd60a09c0..76d68359a4 100644
--- a/hw/sd/sd.c
+++ b/hw/sd/sd.c
@@ -32,6 +32,7 @@
 
 #include "qemu/osdep.h"
 #include "qemu/units.h"
+#include "qemu/cutils.h"
 #include "hw/irq.h"
 #include "hw/registerfields.h"
 #include "sysemu/block-backend.h"
@@ -2106,11 +2107,35 @@ static void sd_realize(DeviceState *dev, Error **errp)
     }
 
     if (sd->blk) {
+        int64_t blk_size;
+
         if (blk_is_read_only(sd->blk)) {
             error_setg(errp, "Cannot use read-only drive as SD card");
             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);
+
+            return;
+        }
+
         ret = blk_set_perm(sd->blk, BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE,
                            BLK_PERM_ALL, errp);
         if (ret < 0) {
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging