[PATCH v2 0/2] USB: EHCI: Add register array bounds to HCS ports

[PATCH v2 0/2] USB: EHCI: Add register array bounds to HCS ports

[Kees Cook]

Hi,

This is cleaning up some of the remaining things to be able to apply
-Warray-bounds and -Wzero-length-bounds globally. Only after doing my
own version of the port_status patch did I find Arnd's earlier
patches, including for the weird Broadcom stuff[1].

No binary differences.

v2:
- use 0x80 as base for brcm registers (stern)
- switch HCS_N_PORTS_MAX to decimal (stern)
- update various comments (stern)
v1: https://lore.kernel.org/lkml/20210818043035.1308062-1-keescook@chromium.org

Thanks!

-Kees

[1] https://lore.kernel.org/lkml/20200527134320.869042-1-arnd@arndb.de/#t

Kees Cook (2):
  USB: EHCI: Add register array bounds to HCS ports
  USB: EHCI: Add alias for Broadcom INSNREG

 drivers/usb/host/ehci-brcm.c | 11 ++++-------
 include/linux/usb/ehci_def.h | 33 +++++++++++++++++++++------------
 2 files changed, 25 insertions(+), 19 deletions(-)

-- 
2.30.2

[PATCH v2 1/2] USB: EHCI: Add register array bounds to HCS ports

[Kees Cook]

The original EHCI register struct used a trailing 0-element array for
addressing the N_PORTS-many available registers. However, after commit
a46af4ebf9ff ("USB: EHCI: define extension registers like normal ones")
the 0-element array started to overlap the USBMODE extension register.

To avoid future compile-time warnings about accessing indexes within a
0-element array, rearrange the struct to actually describe the expected
layout (max 15 registers) with a union. All offsets remain the same, and
bounds checking becomes possible on accesses to port_status and hostpc.

There are no binary differences, and struct offsets continue to match.
"pahole --hex -C ehci_regs" before:

struct ehci_regs {
	u32                        command;              /*     0   0x4 */
	u32                        status;               /*   0x4   0x4 */
	u32                        intr_enable;          /*   0x8   0x4 */
	u32                        frame_index;          /*   0xc   0x4 */
	u32                        segment;              /*  0x10   0x4 */
	u32                        frame_list;           /*  0x14   0x4 */
	u32                        async_next;           /*  0x18   0x4 */
	u32                        reserved1[2];         /*  0x1c   0x8 */
	u32                        txfill_tuning;        /*  0x24   0x4 */
	u32                        reserved2[6];         /*  0x28  0x18 */
	/* --- cacheline 1 boundary (64 bytes) --- */
	u32                        configured_flag;      /*  0x40   0x4 */
	u32                        port_status[0];       /*  0x44     0 */
	u32                        reserved3[9];         /*  0x44  0x24 */
	u32                        usbmode;              /*  0x68   0x4 */
	u32                        reserved4[6];         /*  0x6c  0x18 */
	/* --- cacheline 2 boundary (128 bytes) was 4 bytes ago --- */
	u32                        hostpc[0];            /*  0x84     0 */
	u32                        reserved5[17];        /*  0x84  0x44 */
	/* --- cacheline 3 boundary (192 bytes) was 8 bytes ago --- */
	u32                        usbmode_ex;           /*  0xc8   0x4 */

	/* size: 204, cachelines: 4, members: 18 */
	/* last cacheline: 12 bytes */
};

after:

struct ehci_regs {
	u32                        command;              /*     0   0x4 */
	u32                        status;               /*   0x4   0x4 */
	u32                        intr_enable;          /*   0x8   0x4 */
	u32                        frame_index;          /*   0xc   0x4 */
	u32                        segment;              /*  0x10   0x4 */
	u32                        frame_list;           /*  0x14   0x4 */
	u32                        async_next;           /*  0x18   0x4 */
	u32                        reserved1[2];         /*  0x1c   0x8 */
	u32                        txfill_tuning;        /*  0x24   0x4 */
	u32                        reserved2[6];         /*  0x28  0x18 */
	/* --- cacheline 1 boundary (64 bytes) --- */
	u32                        configured_flag;      /*  0x40   0x4 */
	union {
		u32                port_status[15];      /*  0x44  0x3c */
		struct {
			u32        reserved3[9];         /*  0x44  0x24 */
			u32        usbmode;              /*  0x68   0x4 */
		};                                       /*  0x44  0x28 */
	};                                               /*  0x44  0x3c */
	/* --- cacheline 2 boundary (128 bytes) --- */
	u32                        reserved4;            /*  0x80   0x4 */
	u32                        hostpc[15];           /*  0x84  0x3c */
	/* --- cacheline 3 boundary (192 bytes) --- */
	u32                        reserved5[2];         /*  0xc0   0x8 */
	u32                        usbmode_ex;           /*  0xc8   0x4 */

	/* size: 204, cachelines: 4, members: 16 */
	/* last cacheline: 12 bytes */
};

With this fixed, adding -Wzero-length-bounds to the build no longer
produces several warnings like this:

In file included from drivers/usb/host/ehci-hcd.c:306:
drivers/usb/host/ehci-hub.c: In function 'ehci_port_handed_over':
drivers/usb/host/ehci-hub.c:1194:8: warning: array subscript '<unknown>' is outside the bounds of an interior zero-length array 'u32[0]' {aka 'unsigned int[]'} [-Wzero-length-bounds]
 1194 |  reg = &ehci->regs->port_status[portnum - 1];
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/usb/host/ehci.h:274,
                 from drivers/usb/host/ehci-hcd.c:97:
./include/linux/usb/ehci_def.h:130:7: note: while referencing 'port_status'
  130 |  u32  port_status[0]; /* up to N_PORTS */
      |       ^~~~~~~~~~~

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Al Cooper <alcooperx@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/usb/ehci_def.h | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/include/linux/usb/ehci_def.h b/include/linux/usb/ehci_def.h
index 78e006355557..dcbe2b068569 100644
--- a/include/linux/usb/ehci_def.h
+++ b/include/linux/usb/ehci_def.h
@@ -45,6 +45,7 @@ struct ehci_caps {
 #define HCS_PORTROUTED(p)	((p)&(1 << 7))	/* true: port routing */
 #define HCS_PPC(p)		((p)&(1 << 4))	/* true: port power control */
 #define HCS_N_PORTS(p)		(((p)>>0)&0xf)	/* bits 3:0, ports on HC */
+#define HCS_N_PORTS_MAX		15		/* N_PORTS valid 0x1-0xF */
 
 	u32		hcc_params;      /* HCCPARAMS - offset 0x8 */
 /* EHCI 1.1 addendum */
@@ -126,8 +127,9 @@ struct ehci_regs {
 	u32		configured_flag;
 #define FLAG_CF		(1<<0)		/* true: we'll support "high speed" */
 
-	/* PORTSC: offset 0x44 */
-	u32		port_status[0];	/* up to N_PORTS */
+	union {
+		/* PORTSC: offset 0x44 */
+		u32	port_status[HCS_N_PORTS_MAX];	/* up to N_PORTS */
 /* EHCI 1.1 addendum */
 #define PORTSC_SUSPEND_STS_ACK 0
 #define PORTSC_SUSPEND_STS_NYET 1
@@ -164,28 +166,28 @@ struct ehci_regs {
 #define PORT_CSC	(1<<1)		/* connect status change */
 #define PORT_CONNECT	(1<<0)		/* device connected */
 #define PORT_RWC_BITS   (PORT_CSC | PORT_PEC | PORT_OCC)
-
-	u32		reserved3[9];
-
-	/* USBMODE: offset 0x68 */
-	u32		usbmode;	/* USB Device mode */
+		struct {
+			u32	reserved3[9];
+			/* USBMODE: offset 0x68 */
+			u32	usbmode;	/* USB Device mode */
+		};
 #define USBMODE_SDIS	(1<<3)		/* Stream disable */
 #define USBMODE_BE	(1<<2)		/* BE/LE endianness select */
 #define USBMODE_CM_HC	(3<<0)		/* host controller mode */
 #define USBMODE_CM_IDLE	(0<<0)		/* idle state */
-
-	u32		reserved4[6];
+	};
+	u32		reserved4;
 
 /* Moorestown has some non-standard registers, partially due to the fact that
  * its EHCI controller has both TT and LPM support. HOSTPCx are extensions to
  * PORTSCx
  */
 	/* HOSTPC: offset 0x84 */
-	u32		hostpc[0];	/* HOSTPC extension */
+	u32		hostpc[HCS_N_PORTS_MAX];
 #define HOSTPC_PHCD	(1<<22)		/* Phy clock disable */
 #define HOSTPC_PSPD	(3<<25)		/* Port speed detection */
 
-	u32		reserved5[17];
+	u32		reserved5[2];
 
 	/* USBMODE_EX: offset 0xc8 */
 	u32		usbmode_ex;	/* USB Device mode extension */
-- 
2.30.2

[PATCH v2 2/2] USB: EHCI: Add alias for Broadcom INSNREG

[Kees Cook]

Refactor struct ehci_regs to avoid accessing beyond the end of
port_status. This change results in no difference in the final
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 was
confusing. If "USB_EHCI_INSNREG00" is at port_status[0x0f], its offset
would be 0x80 (not 0x90). The comments have been adjusted to fix this
apparent typo.

Cc: Al Cooper <alcooperx@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Cc: bcm-kernel-feedback-list@broadcom.com
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 9df231511bd6 ("usb: ehci: Add new EHCI driver for Broadcom STB SoC's")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/usb/host/ehci-brcm.c | 11 ++++-------
 include/linux/usb/ehci_def.h | 13 ++++++++++---
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/host/ehci-brcm.c b/drivers/usb/host/ehci-brcm.c
index 3e0ebe8cc649..d3626bfa966b 100644
--- a/drivers/usb/host/ehci-brcm.c
+++ b/drivers/usb/host/ehci-brcm.c
@@ -108,10 +108,9 @@ static int ehci_brcm_reset(struct usb_hcd *hcd)
 	/*
 	 * SWLINUX-1705: Avoid OUT packet underflows during high memory
 	 *   bus usage
-	 * port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x90
 	 */
-	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[1]);
+	ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[3]);
 
 	return ehci_setup(hcd);
 }
@@ -223,11 +222,9 @@ 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
 	 */
-	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[1]);
+	ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[3]);
 
 	ehci_resume(hcd, false);
 
diff --git a/include/linux/usb/ehci_def.h b/include/linux/usb/ehci_def.h
index dcbe2b068569..c892c5bc6638 100644
--- a/include/linux/usb/ehci_def.h
+++ b/include/linux/usb/ehci_def.h
@@ -176,16 +176,23 @@ struct ehci_regs {
 #define USBMODE_CM_HC	(3<<0)		/* host controller mode */
 #define USBMODE_CM_IDLE	(0<<0)		/* idle state */
 	};
-	u32		reserved4;
 
 /* Moorestown has some non-standard registers, partially due to the fact that
  * its EHCI controller has both TT and LPM support. HOSTPCx are extensions to
  * PORTSCx
  */
-	/* HOSTPC: offset 0x84 */
-	u32		hostpc[HCS_N_PORTS_MAX];
+	union {
+		struct {
+			u32	reserved4;
+			/* 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 */
+		};
+
+		/* Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x80 */
+		u32	brcm_insnreg[4];
+	};
 
 	u32		reserved5[2];
 
-- 
2.30.2

Re: [PATCH v2 0/2] USB: EHCI: Add register array bounds to HCS ports

[Alan Stern]

On Wed, Aug 18, 2021 at 10:30:16AM -0700, Kees Cook wrote:
> Hi,
> 
> This is cleaning up some of the remaining things to be able to apply
> -Warray-bounds and -Wzero-length-bounds globally. Only after doing my
> own version of the port_status patch did I find Arnd's earlier
> patches, including for the weird Broadcom stuff[1].
> 
> No binary differences.
> 
> v2:
> - use 0x80 as base for brcm registers (stern)
> - switch HCS_N_PORTS_MAX to decimal (stern)
> - update various comments (stern)
> v1: https://lore.kernel.org/lkml/20210818043035.1308062-1-keescook@chromium.org
> 
> Thanks!
> 
> -Kees
> 
> [1] https://lore.kernel.org/lkml/20200527134320.869042-1-arnd@arndb.de/#t
> 
> Kees Cook (2):
>   USB: EHCI: Add register array bounds to HCS ports
>   USB: EHCI: Add alias for Broadcom INSNREG
> 
>  drivers/usb/host/ehci-brcm.c | 11 ++++-------
>  include/linux/usb/ehci_def.h | 33 +++++++++++++++++++++------------
>  2 files changed, 25 insertions(+), 19 deletions(-)

For both patches:

Acked-by: Alan Stern <stern@rowland.harvard.edu>