USB: EHCI: Add register array bounds to HCS ports
The original EHCI register struct used a trailing 0-element array for
addressing the N_PORTS-many available registers. However, after commit
a46af4ebf9 ("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
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210818173018.2259231-2-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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