Re: [PATCH v3 3/3] PCI/sysfs: Prohibit unaligned access to I/O port on non-x86

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

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On Thu, 8 Jan 2026, duziming wrote:

> 
> 在 2026/1/8 16:56, David Laight 写道:
> > On Thu, 8 Jan 2026 09:59:44 +0800
> > Ziming Du <duziming2@huawei.com> 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
> > > 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
> > > 
> > > Powerpc seems affected as well, so prohibit the unaligned access
> > > on non-x86 archs.
> > I'm not sure it makes any real sense for x86 either.
> > IIRC io space is just like memory space, so a 16bit io access looks the
> > same as two 8bit accesses to an 8bit device (some put the 'data fifo' on
> > addresses 0 and 1 so the code could use 16bit io accesses to speed things
> > up).
> > The same will have applied to misaligned accesses.
> > But, in reality, all device registers are aligned.
> > 
> > I'm not sure EFAULT is the best error code though, EINVAL might be better.
> > (EINVAL is returned for other address/size errors.)
> > EFAULT is usually returned for errors accessing the user buffer, a least
> > one unix system raises SIGSEGV whenever EFAULT is returned.
> > 
> Just to confirm: should all architectures prohibit unaligned access to device
> registers?

In my opinion, yes, also x86 should prohibit it (like I already 
expressed but you ignored that comment until now).

-- 
 i.

> > > 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 | 9 +++++++++
> > >   1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 7e697b82c5e1..11d8b7ec4263 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 +1167,20 @@ static ssize_t pci_resource_io(struct file *filp,
> > > struct kobject *kobj,
> > >   			*(u8 *)buf = inb(port);
> > >   		return 1;
> > >   	case 2:
> > > +		#if !defined(CONFIG_X86)
> > > +			if (!IS_ALIGNED(port, count))
> > > +				return -EFAULT;
> > > +		#endif
> > >   		if (write)
> > >   			outw(*(u16 *)buf, port);
> > >   		else
> > >   			*(u16 *)buf = inw(port);
> > >   		return 2;
> > >   	case 4:
> > > +		#if !defined(CONFIG_X86)
> > > +			if (!IS_ALIGNED(port, count))
> > > +				return -EFAULT;
> > > +		#endif
> > >   		if (write)
> > >   			outl(*(u32 *)buf, port);
> > >   		else
>