On 7/7/20 6:06 PM, Peter Maydell wrote: > On Tue, 7 Jul 2020 at 17:04, Alistair Francis <alistai...@gmail.com> wrote: >> >> 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. > > Mmm, I was thinking that. Perhaps > "expecting a power of 2, e.g. %s" > ?
OK, thanks guys! > > thanks > -- PMM >