Re: [PATCH 2/3] PCI/sysfs: Prohibit unaligned access to I/O port on non-x86

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Wed, 17 Dec 2025, duziming wrote:

> 
> 在 2025/12/16 18:43, Ilpo Järvinen 写道:
> > On Tue, 16 Dec 2025, Ziming Du wrote:
> > 
> > > From: Yongqiang Liu <liuyongqiang13@huawei.com>
> > > 
> > > 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
> > > Modules linked in:
> > > CPU: 1 PID: 44230 Comm: syz.1.10955 Not tainted 6.6.0+ #1
> > > Hardware name: linux,dummy-virt (DT)
> > > pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > > pc : __raw_writew arch/arm64/include/asm/io.h:33 [inline]
> > > pc : _outw include/asm-generic/io.h:594 [inline]
> > > pc : logic_outw+0x54/0x218 lib/logic_pio.c:305
> > > lr : _outw include/asm-generic/io.h:593 [inline]
> > > lr : logic_outw+0x40/0x218 lib/logic_pio.c:305
> > > sp : ffff800083097a30
> > > x29: ffff800083097a30 x28: ffffba71ba86e130 x27: 1ffff00010612f93
> > > x26: ffff3bae63b3a420 x25: ffffba71bbf585d0 x24: 0000000000005ac1
> > > x23: 00000000000010c1 x22: ffff3baf0deb6488 x21: 0000000000000002
> > > x20: 00000000000010c1 x19: 0000000000ffbffe x18: 0000000000000000
> > > x17: 0000000000000000 x16: ffffba71b9f44b48 x15: 00000000200002c0
> > > x14: 0000000000000000 x13: 0000000000000000 x12: ffff6775ca80451f
> > > x11: 1fffe775ca80451e x10: ffff6775ca80451e x9 : ffffba71bb78cf2c
> > > x8 : 0000988a357fbae2 x7 : ffff3bae540228f7 x6 : 0000000000000001
> > > x5 : 1fffe775e2b43c78 x4 : dfff800000000000 x3 : ffffba71b9a00000
> > > x2 : ffff80008d22a000 x1 : ffffc58ec6600000 x0 : fffffbfffe8010c1
> > > 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
> > >   call_write_iter include/linux/fs.h:2085 [inline]
> > >   new_sync_write fs/read_write.c:493 [inline]
> > >   vfs_write+0x7bc/0xac8 fs/read_write.c:586
> > >   ksys_write+0x12c/0x270 fs/read_write.c:639
> > >   __do_sys_write fs/read_write.c:651 [inline]
> > >   __se_sys_write fs/read_write.c:648 [inline]
> > >   __arm64_sys_write+0x78/0xb8 fs/read_write.c:648
> > >   __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
> > >   invoke_syscall+0x8c/0x2e0 arch/arm64/kernel/syscall.c:51
> > >   el0_svc_common.constprop.0+0x200/0x2a8 arch/arm64/kernel/syscall.c:134
> > >   do_el0_svc+0x4c/0x70 arch/arm64/kernel/syscall.c:176
> > >   el0_svc+0x44/0x1d8 arch/arm64/kernel/entry-common.c:806
> > >   el0t_64_sync_handler+0x100/0x130 arch/arm64/kernel/entry-common.c:844
> > >   el0t_64_sync+0x3c8/0x3d0 arch/arm64/kernel/entry.S:757
> > > 
> > > Powerpc seems affected as well, so prohibit the unaligned access
> > > on non-x86 archs.
> > > 
> > > 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>
> > > ---
> > >   drivers/pci/pci-sysfs.c | 12 ++++++++++++
> > >   1 file changed, 12 insertions(+)
> > > 
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 7e697b82c5e1..6fa3c9d0e97e 100644
> > > --- a/drivers/pci/pci-sysfs.c
> > > +++ b/drivers/pci/pci-sysfs.c
> > > @@ -1141,6 +1141,13 @@ static int pci_mmap_resource_wc(struct file *filp,
> > > struct kobject *kobj,
> > >   	return pci_mmap_resource(kobj, attr, vma, 1);
> > >   }
> > >   +#if !defined(CONFIG_X86)
> > > +static bool is_unaligned(unsigned long port, size_t size)
> > > +{
> > > +	return port & (size - 1);
> > > +}
> > > +#endif
> > > +
> > >   static ssize_t pci_resource_io(struct file *filp, struct kobject *kobj,
> > >   			       const struct bin_attribute *attr, char *buf,
> > >   			       loff_t off, size_t count, bool write)
> > > @@ -1158,6 +1165,11 @@ static ssize_t pci_resource_io(struct file *filp,
> > > struct kobject *kobj,
> > >   	if (port + count - 1 > pci_resource_end(pdev, bar))
> > >   		return -EINVAL;
> > >   +#if !defined(CONFIG_X86)
> > > +	if (is_unaligned(port, count))
> > > +		return -EFAULT;
> > > +#endif
> > > +
> > This changes return value from -EINVAL -> -EFAULT for some values of count
> > which seems not justified.
> > 
> > To me it's not clear why even x86 should allow unaligned access. This
> > interface is very much geared towards natural alignment and sizing of the
> > reads (e.g. count = 3 leads to -EINVAL), so it feels somewhat artificial
> > to make x86 behave different here from the others.
> 
> Thanks for your review! We verify that when count = 3, the return value will
> not be
> 
> -EFAULT; It will only return -EFAULT in cases of unaligned access.

Oh, then there's even worse problem in your code as your is_aligned() 
assumes size is a power of two value.

Also, is_aligned() seems to be duplicating IS_ALIGNED() (your naming is 
very misleading as it's a prefixless name that overlaps with a generic 
macro with the very same name).

> We conduct a POC on QEMU with the ARM architecture as follows:
> 
> #include <stdio.h>
> #include <fcntl.h>
> #include <unistd.h>
> 
> int main()
> {
>         int fd = open("/sys/bus/pci/devices/0000:00:01.0/resource0", O_RDWR);
>         char buf[] = "1233333";
>         if (fd < 0) {
>                 printf("open failed\n");
>                 return 1;
>         }
> 
>         pwrite(fd, buf, 2, 1);
> 
>         return 0;
> }
> 
> On x86, this does not trigger a kernel panic.
> 
> > >   	switch (count) {
> > >   	case 1:
> > >   		if (write)
> > > 
> 

-- 
 i.