Re: [PATCH] ACPI / CPPC: Replace cppc_attr with kobj_attribute

Rafael J. Wysocki
2021-04-08T17:59:39Z

On Wed, Apr 7, 2021 at 11:32 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> All of the CPPC sysfs show functions are called via indirect call in
> kobj_attr_show(), where they should be of type
>
> ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr, char *buf);
>
> because that is the type of the ->show() member in
> 'struct kobj_attribute' but they are actually of type
>
> ssize_t (*show)(struct kobject *kobj, struct attribute *attr, char *buf);
>
> because of the ->show() member in 'struct cppc_attr', resulting in a
> Control Flow Integrity violation [1].
>
> $ cat /sys/devices/system/cpu/cpu0/acpi_cppc/highest_perf
> 3400
>
> $ dmesg | grep "CFI failure"
> [ 175.970559] CFI failure (target: show_highest_perf+0x0/0x8):
>
> As far as I can tell, the only different between 'struct cppc_attr' and
> 'struct kobj_attribute' aside from the type of the attr parameter is the
> type of the count parameter in the ->store() member (ssize_t vs.
> size_t), which does not actually matter because all of these nodes are
> read-only.
>
> Eliminate 'struct cppc_attr' in favor of 'struct kobj_attribute' to fix
> the violation.
>
> [1]: https://lore.kernel.org/r/20210401233216.2540591-1-samitolvanen@google.com/
>
> Fixes: 158c998ea44b ("ACPI / CPPC: add sysfs support to compute delivered performance")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1343
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> drivers/acpi/cppc_acpi.c | 14 +++-----------
> 1 file changed, 3 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 69057fcd2c04..a5e6fd0bafa1 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -119,23 +119,15 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
> */
> #define NUM_RETRIES 500ULL
>
> -struct cppc_attr {
> - struct attribute attr;
> - ssize_t (*show)(struct kobject *kobj,
> - struct attribute *attr, char *buf);
> - ssize_t (*store)(struct kobject *kobj,
> - struct attribute *attr, const char *c, ssize_t count);
> -};
> -
> #define define_one_cppc_ro(_name) \
> -static struct cppc_attr _name = \
> +static struct kobj_attribute _name = \
> __ATTR(_name, 0444, show_##_name, NULL)
>
> #define to_cpc_desc(a) container_of(a, struct cpc_desc, kobj)
>
> #define show_cppc_data(access_fn, struct_name, member_name) \
> static ssize_t show_##member_name(struct kobject *kobj, \
> - struct attribute *attr, char *buf) \
> + struct kobj_attribute *attr, char *buf) \
> { \
> struct cpc_desc *cpc_ptr = to_cpc_desc(kobj); \
> struct struct_name st_name = {0}; \
> @@ -161,7 +153,7 @@ show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, reference_perf);
> show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, wraparound_time);
>
> static ssize_t show_feedback_ctrs(struct kobject *kobj,
> - struct attribute *attr, char *buf)
> + struct kobj_attribute *attr, char *buf)
> {
> struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
> struct cppc_perf_fb_ctrs fb_ctrs = {0};
>
> base-commit: 454859c552da78b0f587205d308401922b56863e
> --

Applied as 5.13 material, thanks!