linux-kernel - Re: [PATCH] ACPI / CPPC: Replace cppc_attr with kobj

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Date:   Thu, 8 Apr 2021 19:59:27 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] ACPI / CPPC: Replace cppc_attr with kobj_attribute

On Wed, Apr 7, 2021 at 11:32 PM Nathan Chancellor <nathan@...nel.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@...nel.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!