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Date: Thu, 22 Dec 2022 12:52:42 +0100
From: Ladislav Michl <oss-lists@...ops.cz>
To: Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc: Jimmy Hu <hhhuuu@...gle.com>, mathias.nyman@...el.com,
gregkh@...uxfoundation.org, badhri@...gle.com,
linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH v2] usb: xhci: Check endpoint is valid before
dereferencing it
On Thu, Dec 22, 2022 at 01:08:47PM +0200, Mathias Nyman wrote:
> On 22.12.2022 11.01, Ladislav Michl wrote:
> > On Thu, Dec 22, 2022 at 07:29:12AM +0000, Jimmy Hu wrote:
> > > When the host controller is not responding, all URBs queued to all
> > > endpoints need to be killed. This can cause a kernel panic if we
> > > dereference an invalid endpoint.
> > >
> > > Fix this by using xhci_get_virt_ep() helper to find the endpoint and
> > > checking if the endpoint is valid before dereferencing it.
> > >
> > > [233311.853271] xhci-hcd xhci-hcd.1.auto: xHCI host controller not responding, assume dead
> > > [233311.853393] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000e8
> > >
> > > [233311.853964] pc : xhci_hc_died+0x10c/0x270
> > > [233311.853971] lr : xhci_hc_died+0x1ac/0x270
> > >
> > > [233311.854077] Call trace:
> > > [233311.854085] xhci_hc_died+0x10c/0x270
> > > [233311.854093] xhci_stop_endpoint_command_watchdog+0x100/0x1a4
> > > [233311.854105] call_timer_fn+0x50/0x2d4
> > > [233311.854112] expire_timers+0xac/0x2e4
> > > [233311.854118] run_timer_softirq+0x300/0xabc
> > > [233311.854127] __do_softirq+0x148/0x528
> > > [233311.854135] irq_exit+0x194/0x1a8
> > > [233311.854143] __handle_domain_irq+0x164/0x1d0
> > > [233311.854149] gic_handle_irq.22273+0x10c/0x188
> > > [233311.854156] el1_irq+0xfc/0x1a8
> > > [233311.854175] lpm_cpuidle_enter+0x25c/0x418 [msm_pm]
> > > [233311.854185] cpuidle_enter_state+0x1f0/0x764
> > > [233311.854194] do_idle+0x594/0x6ac
> > > [233311.854201] cpu_startup_entry+0x7c/0x80
> > > [233311.854209] secondary_start_kernel+0x170/0x198
> > >
> > > Fixes: 50e8725e7c42 ("xhci: Refactor command watchdog and fix split string.")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Jimmy Hu <hhhuuu@...gle.com>
> > > ---
> > > drivers/usb/host/xhci-ring.c | 5 ++++-
> > > 1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> > > index ddc30037f9ce..f5b0e1ce22af 100644
> > > --- a/drivers/usb/host/xhci-ring.c
> > > +++ b/drivers/usb/host/xhci-ring.c
> > > @@ -1169,7 +1169,10 @@ static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci,
> > > struct xhci_virt_ep *ep;
> > > struct xhci_ring *ring;
> > > - ep = &xhci->devs[slot_id]->eps[ep_index];
> > > + ep = xhci_get_virt_ep(xhci, slot_id, ep_index);
> > > + if (!ep)
> > > + return;
> > > +
> >
> > xhci_get_virt_ep also adds check for slot_id == 0. It changes behaviour,
> > do we really want to skip that slot? Original code went from 0 to
> > MAX_HC_SLOTS-1.
> >
> > It seems to be off by one to me. Am I missing anything?
>
> slot_id 0 is always invalid, so this is a good change.
I see. Now reading more carefully:
#define HCS_MAX_SLOTS(p) (((p) >> 0) & 0xff)
#define MAX_HC_SLOTS 256
So the loop should go:
for (i = 1; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++)
> > Also, what about passing ep directly to xhci_kill_endpoint_urbs
> > and do the check in xhci_hc_died? Not even compile tested:
>
> passing ep to a function named kill_endpoint_urbs() sound like the
> right thing to do, but as a generic change.
>
> I think its a good idea to first do a targeted fix for this null pointer
> issue that we can send to stable fist.
Agree. But I still do not understand the root cause. There is a check
for NULL xhci->devs[i] already, so patch does not add much more, except
for test for slot_id == 0. And the eps array is just array of
struct xhci_virt_ep, not a pointers to them, so &xhci->devs[i]->eps[j]
should be always valid pointer. However struct xhci_ring in each eps
is allocated and not protected by any lock here. Is that correct?
> > diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> > index ddc30037f9ce..5dac483c562a 100644
> > --- a/drivers/usb/host/xhci-ring.c
> > +++ b/drivers/usb/host/xhci-ring.c
> > @@ -1162,14 +1162,12 @@ static void xhci_kill_ring_urbs(struct xhci_hcd *xhci, struct xhci_ring *ring)
> > }
> > static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci,
> > - int slot_id, int ep_index)
> > + struct xhci_virt_ep *ep)
> > {
> > struct xhci_td *cur_td;
> > struct xhci_td *tmp;
> > - struct xhci_virt_ep *ep;
> > struct xhci_ring *ring;
> > - ep = &xhci->devs[slot_id]->eps[ep_index];
> > if ((ep->ep_state & EP_HAS_STREAMS) ||
> > (ep->ep_state & EP_GETTING_NO_STREAMS)) {
> > int stream_id;
> > @@ -1180,18 +1178,12 @@ static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci,
> > if (!ring)
> > continue;
> > - xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
> > - "Killing URBs for slot ID %u, ep index %u, stream %u",
> > - slot_id, ep_index, stream_id);
> > xhci_kill_ring_urbs(xhci, ring);
> > }
> > } else {
> > ring = ep->ring;
> > if (!ring)
> > return;
> > - xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
> > - "Killing URBs for slot ID %u, ep index %u",
> > - slot_id, ep_index);
> > xhci_kill_ring_urbs(xhci, ring);
> > }
> > @@ -1217,6 +1209,7 @@ static void xhci_kill_endpoint_urbs(struct xhci_hcd *xhci,
> > void xhci_hc_died(struct xhci_hcd *xhci)
> > {
> > int i, j;
> > + struct xhci_virt_ep *ep;
> > if (xhci->xhc_state & XHCI_STATE_DYING)
> > return;
> > @@ -1227,11 +1220,14 @@ void xhci_hc_died(struct xhci_hcd *xhci)
> > xhci_cleanup_command_queue(xhci);
> > /* return any pending urbs, remove may be waiting for them */
> > - for (i = 0; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++) {
> > + for (i = 0; i < HCS_MAX_SLOTS(xhci->hcs_params1); i++) {
> > if (!xhci->devs[i])
> > continue;
> > - for (j = 0; j < 31; j++)
> > - xhci_kill_endpoint_urbs(xhci, i, j);
> > + for (j = 0; j < EP_CTX_PER_DEV; j++) {
> > + ep = &xhci->devs[i]->eps[j];
> > + if (ep)
> > + xhci_kill_endpoint_urbs(xhci, ep);
> > + }
>
> This does loop a bit more than the existing code.
> With this change its always HCS_MAX_SLOTS * EP_CTX_PER_DEV.
> Previously best case was just HCS_MAX_SLOTS.
No, that's just the same:
#define EP_CTX_PER_DEV 31
to make clear where that 31 come from. Taken into acount your comment
above, the loop should be
for (i = 1; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++) ...
for (j = 0; j < EP_CTX_PER_DEV; j++) ...
ladis
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