On Tue, Jul 7, 2020 at 6:22 AM Philippe Mathieu-Daudé <f4...@amsat.org> wrote: > > 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. > > Before CVE-2020-13253 fix, this would allow OOB read/write accesses > past the image size end. > > CVE-2020-13253 has been fixed 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 (expecting at least 64 MiB) > > Signed-off-by: Philippe Mathieu-Daudé <f4...@amsat.org> > --- > hw/sd/sd.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/hw/sd/sd.c b/hw/sd/sd.c > index cb81487e5c..c45106b78e 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" > @@ -2130,11 +2131,26 @@ 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 = size_to_str(blk_size); > + char *blk_size_aligned_str = size_to_str(blk_size_aligned); > + > + error_setg(errp, "Invalid SD card size: %s (expecting at least > %s)", > + blk_size_str, blk_size_aligned_str);
Should we print that we expect a power of 2? This isn't always obvious from the message. Alistair > + g_free(blk_size_str); > + g_free(blk_size_aligned_str); > + return; > + } > + > ret = blk_set_perm(sd->blk, BLK_PERM_CONSISTENT_READ | > BLK_PERM_WRITE, > BLK_PERM_ALL, errp); > if (ret < 0) { > -- > 2.21.3 > >