On Wed, Aug 18, 2021 at 10:57:36AM -0400, Alan Stern wrote:
> On Tue, Aug 17, 2021 at 09:30:34PM -0700, Kees Cook wrote:
> > Refactor struct ehci_regs to avoid accessing beyond the end of
> > port_status. This change results in no difference in the resulting
> > object code.
> >
> > Avoids several warnings when building with -Warray-bounds:
> >
> > drivers/usb/host/ehci-brcm.c: In function 'ehci_brcm_reset':
> > drivers/usb/host/ehci-brcm.c:113:32: warning: array subscript 16 is above array bounds of 'u32[15]' {aka 'unsigned int[15]'} [-Warray-bounds]
> > 113 | ehci_writel(ehci, 0x00800040, &ehci->regs->port_status[0x10]);
> > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > In file included from drivers/usb/host/ehci.h:274,
> > from drivers/usb/host/ehci-brcm.c:15:
> > ./include/linux/usb/ehci_def.h:132:7: note: while referencing 'port_status'
> > 132 | u32 port_status[HCS_N_PORTS_MAX];
> > | ^~~~~~~~~~~
> >
> > Note that the documentation around this proprietary register is
> > confusing. If "USB_EHCI_INSNREG00" is at port_status[0x0f], its offset
> > would be 0x80 (not 0x90). The code uses port_status[0x10], so is that
> > not using "USB_EHCI_INSNREG00"?
>
> I suspect the 0x90 value in the comment is a typo for 0x80.
That'd be my conclusion too. I've updated this for v2.
>
> > Perhaps port_status[0x10] is USB_EHCI_INSNREG01 and port_status[0x12]
> > is USB_EHCI_INSNREG03? If so, the union could be adjusted to better
> > represent the layout.
> >
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Al Cooper <alcooperx@xxxxxxxxx>
> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > Cc: linux-usb@xxxxxxxxxxxxxxx
> > Cc: bcm-kernel-feedback-list@xxxxxxxxxxxx
> > Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
> > Fixes: 9df231511bd6 ("usb: ehci: Add new EHCI driver for Broadcom STB SoC's")
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> > drivers/usb/host/ehci-brcm.c | 11 +++++------
> > include/linux/usb/ehci_def.h | 16 ++++++++++++++--
> > 2 files changed, 19 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/usb/host/ehci-brcm.c b/drivers/usb/host/ehci-brcm.c
> > index 3e0ebe8cc649..5d232d3701f9 100644
> > --- a/drivers/usb/host/ehci-brcm.c
> > +++ b/drivers/usb/host/ehci-brcm.c
> > @@ -110,8 +110,8 @@ static int ehci_brcm_reset(struct usb_hcd *hcd)
> > * bus usage
> > * port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x90
>
> This last comment line is no longer necessary, thanks to the revised
> port definitions. And since it is actively misleading, with the 0x90
> instead of 0x80, I think it should be removed entirely.
Done.
>
> > */
> > - ehci_writel(ehci, 0x00800040, &ehci->regs->port_status[0x10]);
> > - ehci_writel(ehci, 0x00000001, &ehci->regs->port_status[0x12]);
> > + ehci_writel(ehci, 0x00800040, &ehci->regs->brcm_insnreg[0]);
> > + ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[2]);
> >
> > return ehci_setup(hcd);
> > }
> > @@ -223,11 +223,10 @@ static int __maybe_unused ehci_brcm_resume(struct device *dev)
> > /*
> > * SWLINUX-1705: Avoid OUT packet underflows during high memory
> > * bus usage
> > - * port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00
> > - * @ 0x90
> > + * port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x90
>
> Same here.
>
> > */
> > - ehci_writel(ehci, 0x00800040, &ehci->regs->port_status[0x10]);
> > - ehci_writel(ehci, 0x00000001, &ehci->regs->port_status[0x12]);
> > + ehci_writel(ehci, 0x00800040, &ehci->regs->brcm_insnreg[0]);
> > + ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[2]);
> >
> > ehci_resume(hcd, false);
> >
> > diff --git a/include/linux/usb/ehci_def.h b/include/linux/usb/ehci_def.h
> > index 5398f571113b..86f0909cab99 100644
> > --- a/include/linux/usb/ehci_def.h
> > +++ b/include/linux/usb/ehci_def.h
> > @@ -182,11 +182,23 @@ struct ehci_regs {
> > * its EHCI controller has both TT and LPM support. HOSTPCx are extensions to
> > * PORTSCx
> > */
> > - /* HOSTPC: offset 0x84 */
> > - u32 hostpc[HCS_N_PORTS_MAX];
> > + union {
> > + /* HOSTPC: offset 0x84 */
> > + u32 hostpc[HCS_N_PORTS_MAX];
> > #define HOSTPC_PHCD (1<<22) /* Phy clock disable */
> > #define HOSTPC_PSPD (3<<25) /* Port speed detection */
> >
> > + /*
> > + * This was originally documented as:
> > + * "port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x90"
> > + * but this doesn't make sense: the code was using
> > + * port_status[0x10]. port_status[0x0f] would be reserved4.
> > + * Also, none of these are near 0x90. port_status[0x10] is
> > + * offset 0x84, and port_status[0x0f] would be 0x80.
> > + */
>
> This comment is entirely inappropriate. It's the sort of thing that
> belongs in the git history, not in the code.
I wanted it to be easily discoverable, but since we've got a preferred
result now, I'm dropping this and orienting against 0x80.
>
> > + u32 brcm_insnreg[3];
>
> Given the notation in the original comments, perhaps it would be better
> to define this as:
>
> struct { /* Broadcom proprietary registers */
> u32 brcm_insnreg01; /* offset 0x84 */
> u32 brcm_insnreg02;
> u32 brcm_insnreg03;
> };
Following the other register arrays, I'm going to keep an array for
this, but adjust the numbering to start at 0 @ 0x80 so the code will
poke offset 1 and 3.
> I don't know. It would be nice to hear from somebody at Broadcom.
Agreed. :)
Thanks for the review!
--
Kees Cook
