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Re: [RFC PATCH-for-5.1 v2] hw/ide: Avoid #DIV/0! FPU exception by settin
From: |
Darren Kenny |
Subject: |
Re: [RFC PATCH-for-5.1 v2] hw/ide: Avoid #DIV/0! FPU exception by setting CD-ROM sector count |
Date: |
Mon, 20 Jul 2020 12:07:47 +0100 |
On Friday, 2020-07-17 at 15:38:47 +02, Philippe Mathieu-Daudé wrote:
> libFuzzer found an undefined behavior (#DIV/0!) in ide_set_sector()
> when using a CD-ROM (reproducer available on the BugLink):
>
> UndefinedBehaviorSanitizer:DEADLYSIGNAL
> ==12163==ERROR: UndefinedBehaviorSanitizer: FPE on unknown address
> 0x5616279cffdc (pc 0x5616279cffdc bp 0x7ffcdaabae90 sp 0x7ffcdaabae30 T12163)
>
> Fix by initializing the CD-ROM number of sectors in ide_dev_initfn().
>
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Fixes: b2df431407 ("ide scsi: Mess with geometry only for hard disk devices")
> BugLink: https://bugs.launchpad.net/qemu/+bug/1887309
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
The changes LGTM, presume the 'shrug' is OK to leave in ;)
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Thanks,
Darren.
> ---
> Since v1:
> - Allow zero-sized drive images (not sure why we need them)
> but display a friendly message that this is unsupported
>
> Unrelated but interesting:
> http://www.physics.udel.edu/~watson/scen103/cdsoln.html
> ---
> hw/ide/qdev.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/hw/ide/qdev.c b/hw/ide/qdev.c
> index 27ff1f7f66..005d73bdb9 100644
> --- a/hw/ide/qdev.c
> +++ b/hw/ide/qdev.c
> @@ -201,6 +201,15 @@ static void ide_dev_initfn(IDEDevice *dev, IDEDriveKind
> kind, Error **errp)
> errp)) {
> return;
> }
> + } else {
> + uint64_t nb_sectors;
> +
> + blk_get_geometry(dev->conf.blk, &nb_sectors);
> + if (!nb_sectors) {
> + warn_report("Drive image of size zero is unsupported for
> 'ide-cd', "
> + "use at your own risk ¯\\_(ツ)_/¯");
> + }
> + dev->conf.secs = nb_sectors;
> }
> if (!blkconf_apply_backend_options(&dev->conf, kind == IDE_CD,
> kind != IDE_CD, errp)) {
> --
> 2.21.3