Messages in this thread Patch in this message | | | From | Valentine Sinitsyn <> | Subject | [PATCH v4 2/2] PCI: Implement custom llseek for sysfs resource entries | Date | Tue, 22 Aug 2023 16:54:55 +0500 |
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Since commit 636b21b50152 ("PCI: Revoke mappings like devmem"), mmappable sysfs entries have started to receive their f_mapping from the iomem pseudo filesystem, so that CONFIG_IO_STRICT_DEVMEM is honored in sysfs (and procfs) as well as in /dev/[k]mem.
This resulted in a userspace-visible regression:
1. Open a sysfs PCI resource file (eg. /sys/bus/pci/devices/*/resource0) 2. Use lseek(fd, 0, SEEK_END) to determine its size
Expected result: a PCI region size is returned. Actual result: 0 is returned.
The reason is that PCI resource files residing in sysfs use generic_file_llseek(), which relies on f_mapping->host inode to get the file size. As f_mapping is now redefined, f_mapping->host points to an anonymous zero-sized iomem_inode which has nothing to do with sysfs file in question.
Implement a custom llseek method for sysfs PCI resources, which is almost the same as proc_bus_pci_lseek() used for procfs entries.
This makes sysfs and procfs entries consistent with regards to seeking, but also introduces userspace-visible changes to seeking PCI resources in sysfs:
- SEEK_DATA and SEEK_HOLE are no longer supported; - Seeking past the end of the file is prohibited while previously offsets up to MAX_NON_LFS were accepted (reading from these offsets was always invalid).
Fixes: 636b21b50152 ("PCI: Revoke mappings like devmem") Cc: stable@vger.kernel.org Signed-off-by: Valentine Sinitsyn <valesini@yandex-team.ru> Acked-by: Bjorn Helgaas <bhelgaas@google.com> --- drivers/pci/pci-sysfs.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c index ab32a91f287b..2b9d93f11dd1 100644 --- a/drivers/pci/pci-sysfs.c +++ b/drivers/pci/pci-sysfs.c @@ -836,6 +836,12 @@ static const struct attribute_group pci_dev_config_attr_group = { }; #ifdef HAVE_PCI_LEGACY + +static loff_t pci_llseek_resource(struct file *filep, + struct kobject *kobj, + struct bin_attribute *attr, + loff_t offset, int whence); + /** * pci_read_legacy_io - read byte(s) from legacy I/O port space * @filp: open sysfs file @@ -967,6 +973,8 @@ void pci_create_legacy_files(struct pci_bus *b) b->legacy_io->attr.mode = 0600; b->legacy_io->read = pci_read_legacy_io; b->legacy_io->write = pci_write_legacy_io; + /* See pci_create_attr() for motivation */ + b->legacy_io->llseek = pci_llseek_resource; b->legacy_io->mmap = pci_mmap_legacy_io; b->legacy_io->f_mapping = iomem_get_mapping; pci_adjust_legacy_attr(b, pci_mmap_io); @@ -981,6 +989,8 @@ void pci_create_legacy_files(struct pci_bus *b) b->legacy_mem->size = 1024*1024; b->legacy_mem->attr.mode = 0600; b->legacy_mem->mmap = pci_mmap_legacy_mem; + /* See pci_create_attr() for motivation */ + b->legacy_io->llseek = pci_llseek_resource; b->legacy_mem->f_mapping = iomem_get_mapping; pci_adjust_legacy_attr(b, pci_mmap_mem); error = device_create_bin_file(&b->dev, b->legacy_mem); @@ -1138,6 +1148,14 @@ static ssize_t pci_write_resource_io(struct file *filp, struct kobject *kobj, return pci_resource_io(filp, kobj, attr, buf, off, count, true); } +static loff_t pci_llseek_resource(struct file *filep, + struct kobject *kobj __always_unused, + struct bin_attribute *attr, + loff_t offset, int whence) +{ + return fixed_size_llseek(filep, offset, whence, attr->size); +} + /** * pci_remove_resource_files - cleanup resource files * @pdev: dev to cleanup @@ -1195,8 +1213,15 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine) res_attr->mmap = pci_mmap_resource_uc; } } - if (res_attr->mmap) + if (res_attr->mmap) { res_attr->f_mapping = iomem_get_mapping; + /* + * generic_file_llseek() consults f_mapping->host to determine + * the file size. As iomem_inode knows nothing about the + * attribute, it's not going to work, so override it as well. + */ + res_attr->llseek = pci_llseek_resource; + } res_attr->attr.name = res_attr_name; res_attr->attr.mode = 0600; res_attr->size = pci_resource_len(pdev, num); -- 2.34.1
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