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

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

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>

Mark