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

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Message-ID: <98ecea9b-ca2f-4ef7-9f1a-848faa9c92a3@huawei.com>
Date: Thu, 8 Jan 2026 19:49:57 +0800
From: duziming <duziming2@...wei.com>
To: David Laight <david.laight.linux@...il.com>
CC: <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <liuyongqiang13@...wei.com>
Subject: Re: [PATCH v3 3/3] PCI/sysfs: Prohibit unaligned access to I/O port
 on non-x86


在 2026/1/8 16:56, David Laight 写道:
> On Thu, 8 Jan 2026 09:59:44 +0800
> Ziming Du <duziming2@...wei.com> wrote:
>
>> From: Yongqiang Liu <liuyongqiang13@...wei.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.
>
> 	David
Just to confirm: should all architectures prohibit unaligned access to 
device registers?
>> Fixes: 8633328be242 ("PCI: Allow read/write access to sysfs I/O port resources")
>> Signed-off-by: Yongqiang Liu <liuyongqiang13@...wei.com>
>> Signed-off-by: Ziming Du <duziming2@...wei.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