Re: [PATCH v3] ACPI: platform-profile: Fix CFI violation when accessing sysfs files

["Mark Pearson" <mpearson-lenovo@squebb.ca>]

On Tue, Feb 11, 2025, at 10:05 AM, Mark Pearson wrote:
> Hi Nathan
>
> On Mon, Feb 10, 2025, at 9:28 PM, Nathan Chancellor wrote:
>> When an attribute group is created with sysfs_create_group(), the
>> ->sysfs_ops() callback is set to kobj_sysfs_ops, which sets the ->show()
>> and ->store() callbacks to kobj_attr_show() and kobj_attr_store()
>> respectively. These functions use container_of() to get the respective
>> callback from the passed attribute, meaning that these callbacks need to
>> be the same type as the callbacks in 'struct kobj_attribute'.
>>
>> However, the platform_profile sysfs functions have the type of the
>> ->show() and ->store() callbacks in 'struct device_attribute', which
>> results a CFI violation when accessing platform_profile or
>> platform_profile_choices under /sys/firmware/acpi because the types do
>> not match:
>>
>>   CFI failure at kobj_attr_show+0x19/0x30 (target: 
>> platform_profile_choices_show+0x0/0x140; expected type: 0x7a69590c)
>>
>> There is no functional issue from the type mismatch because the layout
>> of 'struct kobj_attribute' and 'struct device_attribute' are the same,
>> so the container_of() cast does not break anything aside from CFI.
>>
>> Change the type of platform_profile_choices_show() and
>> platform_profile_{show,store}() to match the callbacks in
>> 'struct kobj_attribute' and update the attribute variables to match,
>> which resolves the CFI violation.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: a2ff95e018f1 ("ACPI: platform: Add platform profile support")
>> Reported-by: John Rowley <lkml@johnrowley.me>
>> Closes: https://github.com/ClangBuiltLinux/linux/issues/2047
>> Tested-by: John Rowley <lkml@johnrowley.me>
>> Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>> ---
>> Changes in v3:
>> - Rebase on 6.14-rc1, which includes updates to the driver to address
>>   Greg's previous concerns but this change is still needed for the
>>   legacy sysfs interface. v2 can be used for the stable backport.
>> - Link to v2: 
>> https://lore.kernel.org/r/20241118-acpi-platform_profile-fix-cfi-violation-v2-1-62ff952804de@kernel.org
>>
>> Changes in v2:
>> - Rebase on linux-pm/acpi
>> - Pick up Sami's reviewed-by tag
>> - Adjust wording around why there is no functional issue from the
>>   mismatched types
>> - Link to v1: 
>> https://lore.kernel.org/r/20240819-acpi-platform_profile-fix-cfi-violation-v1-1-479365d848f6@kernel.org
>> ---
>>  drivers/acpi/platform_profile.c | 26 +++++++++++++-------------
>>  1 file changed, 13 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/acpi/platform_profile.c 
>> b/drivers/acpi/platform_profile.c
>> index fc92e43d0fe9..1b6317f759f9 100644
>> --- a/drivers/acpi/platform_profile.c
>> +++ b/drivers/acpi/platform_profile.c
>> @@ -260,14 +260,14 @@ static int _aggregate_choices(struct device *dev, 
>> void *data)
>> 
>>  /**
>>   * platform_profile_choices_show - Show the available profile choices 
>> for legacy sysfs interface
>> - * @dev: The device
>> + * @kobj: The kobject
>>   * @attr: The attribute
>>   * @buf: The buffer to write to
>>   *
>>   * Return: The number of bytes written
>>   */
>> -static ssize_t platform_profile_choices_show(struct device *dev,
>> -					     struct device_attribute *attr,
>> +static ssize_t platform_profile_choices_show(struct kobject *kobj,
>> +					     struct kobj_attribute *attr,
>>  					     char *buf)
>>  {
>>  	unsigned long aggregate[BITS_TO_LONGS(PLATFORM_PROFILE_LAST)];
>> @@ -333,14 +333,14 @@ static int _store_and_notify(struct device *dev, 
>> void *data)
>> 
>>  /**
>>   * platform_profile_show - Show the current profile for legacy sysfs interface
>> - * @dev: The device
>> + * @kobj: The kobject
>>   * @attr: The attribute
>>   * @buf: The buffer to write to
>>   *
>>   * Return: The number of bytes written
>>   */
>> -static ssize_t platform_profile_show(struct device *dev,
>> -				     struct device_attribute *attr,
>> +static ssize_t platform_profile_show(struct kobject *kobj,
>> +				     struct kobj_attribute *attr,
>>  				     char *buf)
>>  {
>>  	enum platform_profile_option profile = PLATFORM_PROFILE_LAST;
>> @@ -362,15 +362,15 @@ static ssize_t platform_profile_show(struct device *dev,
>> 
>>  /**
>>   * platform_profile_store - Set the profile for legacy sysfs interface
>> - * @dev: The device
>> + * @kobj: The kobject
>>   * @attr: The attribute
>>   * @buf: The buffer to read from
>>   * @count: The number of bytes to read
>>   *
>>   * Return: The number of bytes read
>>   */
>> -static ssize_t platform_profile_store(struct device *dev,
>> -				      struct device_attribute *attr,
>> +static ssize_t platform_profile_store(struct kobject *kobj,
>> +				      struct kobj_attribute *attr,
>>  				      const char *buf, size_t count)
>>  {
>>  	unsigned long choices[BITS_TO_LONGS(PLATFORM_PROFILE_LAST)];
>> @@ -401,12 +401,12 @@ static ssize_t platform_profile_store(struct device *dev,
>>  	return count;
>>  }
>> 
>> -static DEVICE_ATTR_RO(platform_profile_choices);
>> -static DEVICE_ATTR_RW(platform_profile);
>> +static struct kobj_attribute attr_platform_profile_choices = 
>> __ATTR_RO(platform_profile_choices);
>> +static struct kobj_attribute attr_platform_profile = 
>> __ATTR_RW(platform_profile);
>> 
>>  static struct attribute *platform_profile_attrs[] = {
>> -	&dev_attr_platform_profile_choices.attr,
>> -	&dev_attr_platform_profile.attr,
>> +	&attr_platform_profile_choices.attr,
>> +	&attr_platform_profile.attr,
>>  	NULL
>>  };
>> 
>>
>> ---
>> base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
>> change-id: 20240819-acpi-platform_profile-fix-cfi-violation-de278753bd5f
>>
>> Best regards,
>> -- 
>> Nathan Chancellor <nathan@kernel.org>
>
> Just a note to say thank you for noticing my email address change - the 
> old lenovo one was awful to use so I dropped it a while back, but it 
> meant I missed your first two patches (my mail filters for the list 
> should have caught it and I'll have to figure out why not...)
>
> From the V1 patch there was a question about why it was done this way: 
> I believe I just copied how it seems to be done everywhere else in the 
> kernel. I can't remember what I used as a reference exactly, but I went 
> and checked a few random drivers and it seems to be everywhere.
>
> Patch looks fine (I'd like to try it out on my system - will aim to do 
> that today). I didn't know what CFI was (and have lightly educated 
> myself now). 
> Is there a better way to fix this so it's common across all drivers 
> somehow? Updating every individual instance is going to be a lot.
>
> Reviewed-by: Mark Pearson <mpearson-lenovo@squebb.ca>
>
Also:
Tested-by: Mark Pearson <mpearson-lenovo@squebb.ca>

Mark