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Message-ID: <e954fe32-4a6b-458f-97a7-d9fbefc48144@huawei.com>
Date: Wed, 17 Dec 2025 17:47:27 +0800
From: duziming <duziming2@...wei.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>, LKML
<linux-kernel@...r.kernel.org>, <chrisw@...hat.com>,
<jbarnes@...tuousgeek.org>, <alex.williamson@...hat.com>,
<liuyongqiang13@...wei.com>
Subject: Re: [PATCH 2/3] PCI/sysfs: Prohibit unaligned access to I/O port on
non-x86
在 2025/12/16 18:43, Ilpo Järvinen 写道:
> On Tue, 16 Dec 2025, Ziming Du 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
>> 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@...wei.com>
>> Signed-off-by: Ziming Du <duziming2@...wei.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.
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)
>>
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