Re: [PATCH v14 9/9] RFC: fw_cfg: do DMA read operation

From: Marc-Andre Lureau
Date: Wed Feb 14 2018 - 12:08:54 EST


Hi

On Wed, Feb 14, 2018 at 5:59 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> On Wed, Feb 14, 2018 at 05:52:10PM +0100, Marc-Andre Lureau wrote:
>> >> @@ -282,8 +320,9 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
>> >> #endif
>> >>
>> >> /* verify fw_cfg device signature */
>> >> - fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
>> >> - if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
>> >> + if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig,
>> >> + 0, FW_CFG_SIG_SIZE, false) < 0 ||
>> >> + memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
>> >> fw_cfg_io_cleanup();
>> >> return -ENODEV;
>> >> }
>> >
>> > Rather than add dead code, how about a promise not to
>> > fail if dma is disabled? Patch will be smaller then.
>>
>> Even with dma disabled, you could have a locking bug which was
>> silently ignored before and is now taken into account.
>
> I see. I'd start with a patch reporting errors to users then.
> That would be a bugfix and can be merged for this version.

silently is the wrong word for it, there is already a WARN(). However,
the memcmp was done on uninitialzed sig[] (which likely resulted in
returning -ENODEV in the function)

Now it can check if the function failed to read before doing the memcmp.

Hope that clarifies it.

>
>> >
>> >> @@ -466,8 +505,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
>> >> if (count > entry->size - pos)
>> >> count = entry->size - pos;
>> >>
>> >> - fw_cfg_read_blob(entry->select, buf, pos, count);
>> >> - return count;
>> >> + /* do not use DMA, virt_to_phys(buf) might not be ok */
>> >> + return fw_cfg_read_blob(entry->select, buf, pos, count, false);
>> >> }
>> >>
>> >> static struct bin_attribute fw_cfg_sysfs_attr_raw = {
>> >> @@ -632,7 +671,12 @@ static int fw_cfg_register_dir_entries(void)
>> >> struct fw_cfg_file *dir;
>> >> size_t dir_size;
>> >>
>> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count, 0, sizeof(files.count));
>> >> + ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count,
>> >> + 0, sizeof(files.count), false);
>> >> + if (ret < 0) {
>> >> + return ret;
>> >> + }
>> >> +
>> >> count = be32_to_cpu(files.count);
>> >> dir_size = count * sizeof(struct fw_cfg_file);
>> >>
>> >> @@ -640,7 +684,11 @@ static int fw_cfg_register_dir_entries(void)
>> >> if (!dir)
>> >> return -ENOMEM;
>> >>
>> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(files.count), dir_size);
>> >> + ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir,
>> >> + sizeof(files.count), dir_size, false);
>> >> + if (ret < 0) {
>> >> + goto end;
>> >> + }
>> >>
>> >> for (i = 0; i < count; i++) {
>> >> ret = fw_cfg_register_file(&dir[i]);
>> >> @@ -648,6 +696,7 @@ static int fw_cfg_register_dir_entries(void)
>> >> break;
>> >> }
>> >>
>> >> +end:
>> >> kfree(dir);
>> >> return ret;
>> >> }
>> >> @@ -688,7 +737,10 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
>> >> goto err_probe;
>> >>
>> >> /* get revision number, add matching top-level attribute */
>> >> - fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev));
>> >> + err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev), false);
>> >> + if (err < 0) {
>> >> + goto err_probe;
>> >> + }
>> >> fw_cfg_rev = le32_to_cpu(rev);
>> >> err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
>> >> if (err)
>> >> --
>> >> 2.16.1.73.g5832b7e9f2