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When booting with CONFIG_CFI_CLANG, there are numerous violations when
accessing the files under
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/gt/gt0:
$ cd /sys/devices/pci0000:00/0000:00:02.0/drm/card0/gt/gt0
$ grep . *
id:0
punit_req_freq_mhz:350
rc6_enable:1
rc6_residency_ms:214934
rps_act_freq_mhz:1300
rps_boost_freq_mhz:1300
rps_cur_freq_mhz:350
rps_max_freq_mhz:1300
rps_min_freq_mhz:350
rps_RP0_freq_mhz:1300
rps_RP1_freq_mhz:350
rps_RPn_freq_mhz:350
throttle_reason_pl1:0
throttle_reason_pl2:0
throttle_reason_pl4:0
throttle_reason_prochot:0
throttle_reason_ratl:0
throttle_reason_status:0
throttle_reason_thermal:0
throttle_reason_vr_tdc:0
throttle_reason_vr_thermalert:0
$ sudo dmesg &| grep "CFI failure at"
[ 214.595903] CFI failure at kobj_attr_show+0x19/0x30 (target: id_show+0x0/0x70 [i915]; expected type: 0xc527b809)
[ 214.596064] CFI failure at kobj_attr_show+0x19/0x30 (target: punit_req_freq_mhz_show+0x0/0x40 [i915]; expected type: 0xc527b809)
[ 214.596407] CFI failure at kobj_attr_show+0x19/0x30 (target: rc6_enable_show+0x0/0x40 [i915]; expected type: 0xc527b809)
[ 214.596528] CFI failure at kobj_attr_show+0x19/0x30 (target: rc6_residency_ms_show+0x0/0x270 [i915]; expected type: 0xc527b809)
[ 214.596682] CFI failure at kobj_attr_show+0x19/0x30 (target: act_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.596792] CFI failure at kobj_attr_show+0x19/0x30 (target: boost_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.596893] CFI failure at kobj_attr_show+0x19/0x30 (target: cur_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.596996] CFI failure at kobj_attr_show+0x19/0x30 (target: max_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.597099] CFI failure at kobj_attr_show+0x19/0x30 (target: min_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.597198] CFI failure at kobj_attr_show+0x19/0x30 (target: RP0_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.597301] CFI failure at kobj_attr_show+0x19/0x30 (target: RP1_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.597405] CFI failure at kobj_attr_show+0x19/0x30 (target: RPn_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
[ 214.597538] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.597701] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.597836] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.597952] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.598071] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.598177] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.598307] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.598439] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
[ 214.598542] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
With kCFI, indirect calls are validated against their expected type
versus actual type and failures occur when the two types do not match.
The ultimate issue is that these sysfs functions are expecting to be
called via dev_attr_show() but they may also be called via
kobj_attr_show(), as certain files are created under two different
kobjects that have two different sysfs_ops in intel_gt_sysfs_register(),
hence the warnings above. When accessing the gt_ files under
/sys/devices/pci0000:00/0000:00:02.0/drm/card0, which are using the same
sysfs functions, there are no violations, meaning the functions are
being called with the proper type.
To make everything work properly, adjust certain functions to match the
type of the ->show() and ->store() members in 'struct kobj_attribute'.
Add a macro to generate functions for that can be called via both
dev_attr_{show,store}() or kobj_attr_{show,store}() so that they can be
called through both kobject locations without violating kCFI and adjust
the attribute groups to account for this.
Link: https://github.com/ClangBuiltLinux/linux/issues/1716
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221013205909.1282545-1-nathan@kernel.org
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.