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Message-ID: <20210818145736.GD193695@rowland.harvard.edu>
Date: Wed, 18 Aug 2021 10:57:36 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Kees Cook <keescook@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Al Cooper <alcooperx@...il.com>, linux-usb@...r.kernel.org,
bcm-kernel-feedback-list@...adcom.com,
Arnd Bergmann <arnd@...db.de>,
Florian Fainelli <f.fainelli@...il.com>,
Andy Shevchenko <andy.shevchenko@...il.com>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/2] USB: EHCI: Add alias for Broadcom INSNREG
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.
> 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@...uxfoundation.org>
> Cc: Al Cooper <alcooperx@...il.com>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: linux-usb@...r.kernel.org
> Cc: bcm-kernel-feedback-list@...adcom.com
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 9df231511bd6 ("usb: ehci: Add new EHCI driver for Broadcom STB SoC's")
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> 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.
> */
> - 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.
> + 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;
};
I don't know. It would be nice to hear from somebody at Broadcom.
Alan Stern
> + };
> +
> u32 reserved5[2];
>
> /* USBMODE_EX: offset 0xc8 */
> --
> 2.30.2
>
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