[PATCH] PCI/ASPM: Fix NULL pointer dereference in sysfs show/store callbacks

[Shawn Lin]

Reading or writing a link state sysfs attribute after the upstream
bridge's pcie_link_state has been freed triggers a NULL pointer
dereference.

This was first seen on a 6.12 based kernel by userspace stress testing a
PCIe endpoint on an RK3588 EVB1 (Intel I350 dual-port NIC behind the
root port). The same NULL pointer dereference exists in upstream and can
be reproduced reliably on:

  # lspci
  00:00.0 PCI bridge: Rockchip Electronics Co., Ltd RK3588 (rev 01)
  01:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
  01:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)

by running:

  echo 1 > /sys/bus/pci/devices/0000:01:00.0/remove
  cat /sys/bus/pci/devices/0000:01:00.1/link/l1_aspm

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030
Mem abort info:
  ESR = 0x0000000096000004
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x04: level 0 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=0000000106959000
[0000000000000030] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 0000000096000004 [#1]  SMP
Modules linked in:
CPU: 3 UID: 0 PID: 646 Comm: cat Not tainted 7.3.0-rc6-next-20261007-00007-gf2fe32674ebe-dirty #134 PREEMPT(full)
Hardware name: Rockchip RK3588 EVB1 V10 Board (DT)
pstate: 40400009 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : l1_aspm_show+0x64/0x88
lr : dev_attr_show+0x24/0x68
sp : ffff800086f9bbf0
x29: ffff800086f9bbf0 x28: ffff0001036c0000 x27: 0000000000000000
x26: 0000000000000000 x25: 000000007ffff001 x24: 0000000000000001
x23: ffff800081781630 x22: ffff0001008d3c00 x21: ffff0001053b9000
x20: ffff0001020880d0 x19: ffff800082441c28 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 00000000ffffe000
x11: ffff0001053b9000 x10: 0000000000c00010 x9 : 0000000000000070
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000004
x2 : ffff0001053b9000 x1 : ffff800082441c28 x0 : ffff0001053b9000
Call trace:
 l1_aspm_show+0x64/0x88 (P)
 dev_attr_show+0x24/0x68
 sysfs_kf_seq_show+0xb8/0x138
 kernfs_seq_show+0x2c/0x38
 seq_read_iter+0x120/0x3e0
 kernfs_fop_read_iter+0x60/0x188
 vfs_read+0x200/0x2b8
 ksys_read+0x74/0xe8
 __arm64_sys_read+0x1c/0x28
 invoke_syscall+0x44/0xec
 el0_svc_common+0x8c/0xd8
 do_el0_svc+0x1c/0x28
 el0_svc+0x3c/0x98
 el0t_64_sync_handler+0x84/0x12c
 el0t_64_sync+0x198/0x19c
Code: aa1f03e8 d503233f a9bf7bfd 910003fd (b9403108)
 ---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Oops: Fatal exception
SMP: stopping secondary CPUs
Kernel Offset: disabled
CPU features: 0x0,70000000,0070002a,01180a42,0800e20b
Memory Limit: none
 ---[ end Kernel panic - not syncing: Oops: Fatal exception ]---

The sysfs attributes are created for every device below the link, but
the link state is freed by pcie_aspm_exit_link_state() when function 0
of the downstream component is removed. A sibling function or a sysfs
reader still holding a reference can then call into the show/store
callbacks while pcie_aspm_get_link() returns NULL.

aspm_attr_show_common(), aspm_attr_store_common(), clkpm_show() and
clkpm_store() all dereference the link pointer unconditionally. Add the
missing NULL checks, mirroring pcie_aspm_enabled(), and return -ENODEV.

Cc: stable at vger.kernel.org
Fixes: 72ea91afbfb0 ("PCI/ASPM: Add sysfs attributes for controlling ASPM link states")
Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>
---

 drivers/pci/pcie/aspm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index f8e6497..0e0ba0e6 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1777,6 +1777,9 @@ static ssize_t aspm_attr_show_common(struct device *dev,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
 
+	if (!link)
+		return -ENODEV;
+
 	return sysfs_emit(buf, "%d\n", (link->aspm_enabled & state) ? 1 : 0);
 }
 
@@ -1788,6 +1791,9 @@ static ssize_t aspm_attr_store_common(struct device *dev,
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
 	bool state_enable;
 
+	if (!link)
+		return -ENODEV;
+
 	if (kstrtobool(buf, &state_enable) < 0)
 		return -EINVAL;
 
@@ -1836,6 +1842,9 @@ static ssize_t clkpm_show(struct device *dev,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
 
+	if (!link)
+		return -ENODEV;
+
 	return sysfs_emit(buf, "%d\n", link->clkpm_enabled);
 }
 
@@ -1847,6 +1856,9 @@ static ssize_t clkpm_store(struct device *dev,
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
 	bool state_enable;
 
+	if (!link)
+		return -ENODEV;
+
 	if (kstrtobool(buf, &state_enable) < 0)
 		return -EINVAL;
 
-- 
2.7.4