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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Igor Mammedov <imammedo@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: acpi_pcihp_eject_slot() bug if passed 'slots == 0'
Date: Thu, 26 Mar 2020 09:29:41 -0400
Message-ID: <20200326092845-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20200326135041.297de118@redhat.com>

On Thu, Mar 26, 2020 at 01:50:41PM +0100, Igor Mammedov wrote:
> On Thu, 26 Mar 2020 13:29:01 +0100
> Igor Mammedov <imammedo@redhat.com> wrote:
> 
> > On Thu, 26 Mar 2020 11:52:36 +0000
> > Peter Maydell <peter.maydell@linaro.org> wrote:
> > 
> > > Hi; Coverity spots that if hw/acpi/pcihp.c:acpi_pcihp_eject_slot()
> > > is passed a zero 'slots' argument then ctz32(slots) will return 32,
> > > and then the code that does '1U << slot' is C undefined behaviour
> > > because it's an oversized shift. (This is CID 1421896.)
> > > 
> > > Since the pci_write() function in this file can call
> > > acpi_pcihp_eject_slot() with an arbitrary value from the guest,
> > > I think we need to handle 'slots == 0' safely. But what should
> > > the behaviour be?  
> > 
> > 0 is not valid value, we should ignore and return early in this case
> > like we do with bsel. I'll post a path shortly.
> well, looking more that is only true for main bus, for bridges it can be
> slot number can be zero,

It can but we don't allow slot zero hotplug with SHPC
so it's easier if we don't allow this with ACPI either.

> then AML left shifts it and writes into B0EJ
> which traps into pci_write(, data) and that is supposed to eject
> slot 0 according to guest(AML).
> 
> Michael,
> what's your take on it?
> 
> > 
> > > 
> > > thanks
> > > -- PMM
> > >   
> > 
> > 



  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26 11:52 Peter Maydell
2020-03-26 12:29 ` Igor Mammedov
2020-03-26 12:50   ` Igor Mammedov
2020-03-26 13:29     ` Michael S. Tsirkin [this message]
2020-03-26 13:23 ` Igor Mammedov
2020-03-26 13:28   ` Michael S. Tsirkin
2020-03-26 13:31     ` Michael S. Tsirkin
2020-03-26 13:40       ` Igor Mammedov

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