[PATCH v4 1/4] PCI/sysfs: Prohibit unaligned access to I/O port

Ziming Du
2026-01-16T07:52:30Z

Unaligned access is harmful for non-x86 archs such as arm64. When we
use pwrite or pread to access the I/O port resources with unaligned
offset, system will crash as follows:

Unable to handle kernel paging request at virtual address fffffbfffe8010c1
Internal error: Oops: 0000000096000061 [#1] SMP
Call trace:
_outw include/asm-generic/io.h:594 [inline]
logic_outw+0x54/0x218 lib/logic_pio.c:305
pci_resource_io drivers/pci/pci-sysfs.c:1157 [inline]
pci_write_resource_io drivers/pci/pci-sysfs.c:1191 [inline]
pci_write_resource_io+0x208/0x260 drivers/pci/pci-sysfs.c:1181
sysfs_kf_bin_write+0x188/0x210 fs/sysfs/file.c:158
kernfs_fop_write_iter+0x2e8/0x4b0 fs/kernfs/file.c:338
vfs_write+0x7bc/0xac8 fs/read_write.c:586
ksys_write+0x12c/0x270 fs/read_write.c:639
__arm64_sys_write+0x78/0xb8 fs/read_write.c:648

Although x86 might handle unaligned I/O accesses by splitting cycles,
this approach is still limited because PCI device registers typically
expect natural alignment. A global prohibition of unaligned accesses
ensures consistent behavior across all architectures and prevents
unexpected hardware side effects.

Fixes: 8633328be242 ("PCI: Allow read/write access to sysfs I/O port resources")
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: Ziming Du <duziming2@huawei.com>
Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/pci/pci-sysfs.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index c2df915ad2d29..18e5d4603b472 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -31,6 +31,7 @@
#include <linux/of.h>
#include <linux/aperture.h>
#include <linux/unaligned.h>
+#include <linux/align.h>
#include "pci.h"

#ifndef ARCH_PCI_DEV_GROUPS
@@ -1166,12 +1167,16 @@ static ssize_t pci_resource_io(struct file *filp, struct kobject *kobj,
*(u8 *)buf = inb(port);
return 1;
case 2:
+ if (!IS_ALIGNED(port, count))
+ return -EINVAL;
if (write)
outw(*(u16 *)buf, port);
else
*(u16 *)buf = inw(port);
return 2;
case 4:
+ if (!IS_ALIGNED(port, count))
+ return -EINVAL;
if (write)
outl(*(u32 *)buf, port);
else
--
2.43.0