[PATCH] usb: xhci: validate CAPLENGTH in xhci_gen_setup()

[erdaitianjiao]

xhci_hcd can be bound to arbitrary PCI devices via the
driver_override sysfs knob. When this happens to a device whose
MMIO registers are not xHCI capability registers,
xhci_gen_setup() reads CAPLENGTH from the foreign register
layout and uses it as a byte offset to compute op_regs.

A non-xHCI device can return a CAPLENGTH value that is
  - not large enough to fit the capability register block, or
  - not 4-byte aligned (e.g. the NVMe CAP register's low byte is
    0xff, which becomes CAPLENGTH = 0xff).

The unaligned case is especially harmful on arm64: MMIO is
Device memory and Device-nGnRE accesses require natural
alignment, so readl(&op_regs->command) faults with an
alignment exception even when the address is within the
ioremapped region.

Validate CAPLENGTH in xhci_gen_setup() and fail probe with
-ENODEV if the value is smaller than 0x20 (capability registers
are 32 bytes per the xHCI spec), not 4-byte aligned, or leaves
no room for the operational register space within the mapped
region.

The run_regs_off read on the next line has the same shape, but
is not reachable on the xhci_halt code path and is left
untouched here.

Reproduced on a QEMU virt machine with a syzkaller repro that
unbinds the NVMe driver on 0000:00:02.0 and binds xhci_hcd via
driver_override. Before this patch the kernel Oopses and
panics; after, the probe is rejected cleanly (verified with 46
consecutive probe attempts, zero Oopses).

Reported-by: syzbot+c90273bf9017ef1462af@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?id=44c85514940262c7e2fad6f8fd0c07d8f2884154
Fixes: 552e0c4f12fe ("usb/xhci: move xhci_gen_setup() away from -pci.")
Signed-off-by: erdaitianjiao <erdaitianjiao@xxxxxxxxx>
---
 drivers/usb/host/xhci.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 091c82ca8ee2..fb0075d0530f 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -5432,7 +5432,7 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
 	 */
 	struct device		*dev = hcd->self.sysdev;
 	int			retval;
-	u32			hcs_params1;
+	u32			hcs_params1, capbase;
 
 	/* Accept arbitrarily long scatter-gather lists */
 	hcd->self.sg_tablesize = ~0;
@@ -5453,8 +5453,16 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
 	mutex_init(&xhci->mutex);
 	xhci->main_hcd = hcd;
 	xhci->cap_regs = hcd->regs;
-	xhci->op_regs = hcd->regs +
-		HC_LENGTH(readl(&xhci->cap_regs->hc_capbase));
+	capbase = readl(&xhci->cap_regs->hc_capbase);
+	if (HC_LENGTH(capbase) < 0x20 ||
+	    (HC_LENGTH(capbase) & 0x3) ||
+	    (hcd->rsrc_len &&
+	     HC_LENGTH(capbase) + sizeof(struct xhci_op_regs) > hcd->rsrc_len)) {
+		xhci_err(xhci, "Invalid CAPLENGTH %#x (rsrc_len %#lx)
",
+			 HC_LENGTH(capbase), (unsigned long)hcd->rsrc_len);
+		return -ENODEV;
+	}
+	xhci->op_regs = hcd->regs + HC_LENGTH(capbase);
 	xhci->run_regs = hcd->regs +
 		(readl(&xhci->cap_regs->run_regs_off) & RTSOFF_MASK);
 	/* Cache read-only capability registers */
-- 
2.55.0