[PATCH v6 0/5] asdf

Kees Cook
2025-12-03T23:30:40Z

Hi,

Here's an update for the kmalloc_obj() API proposal based on Linus's
feedback. I normally wouldn't send this during the merge window,
but I wanted to have it updated for discussion at LPC[1] (and here in
email). Please see patches 1 and 4 for the bulk of the details. This is
obviously not v6.19 material! :)

Replacing[2] all existing simple code patterns found via Coccinelle
shows what could be replaced immediately (also saving roughly 1000 lines):

7971 files changed, 19880 insertions(+), 20752 deletions(-)

This would take us from 24515 size-based k*alloc assignments to 7682:

$ git grep ' = kv\?[mzcv]alloc\(\|_array\)(' | wc -l
24515
$ git reset --hard HEAD^
HEAD is now at 8bccc91e6cdf treewide: kmalloc_obj conversion
$ git grep ' = kv\?[mzcv]alloc\(\|_array\)(' | wc -l
7682

This treewide change could be done at the end of the merge window just
before -rc1 is released (as is common for treewide changes). Handling
this API change in backports to -stable should be possible without much
hassle by backporting the __flex_counter() patch and this patch, while
taking conversions as-needed.

The impact on my bootable testing image size (with the treewide patch
applied) is tiny. With both GCC 13 (no __counted_by support) and GCC 15
(with __counted_by) the images are actually very slightly smaller:

$ size -G gcc-boot/vmlinux.gcc*
text data bss total filename
29975593 21527689 16601200 68104482 gcc-boot/vmlinux.gcc13-before
29969263 21528663 16601112 68099038 gcc-boot/vmlinux.gcc13-after
30555626 21291299 17086620 68933545 gcc-boot/vmlinux.gcc15-before
30550144 21292039 17086540 68928723 gcc-boot/vmlinux.gcc15-after

Thanks!

-Kees

[1] https://lpc.events/event/19/contributions/2136/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=dev/v6.18-rc6/alloc_obj/v5&id=f79ee96ad6a3cafdb274fe15d3ae067724e72327

v6:
- Drop _sz() helpers and simplify the resulting internals
- Split _flex() helper into its own patch to make review easier
- Explicitly use TYPE within the internals to make things more readable
- Move treewide change details into the cover letter
v5: https://lore.kernel.org/lkml/20251122014258.do.018-kees@kernel.org/
v4: https://lore.kernel.org/lkml/20250315025852.it.568-kees@kernel.org/
v3: https://lore.kernel.org/lkml/20240822231324.make.666-kees@kernel.org/
v2: https://lore.kernel.org/lkml/20240807235433.work.317-kees@kernel.org/
v1: https://lore.kernel.org/lkml/20240719192744.work.264-kees@kernel.org/

Kees Cook (5):
slab: Introduce kmalloc_obj() and family
checkpatch: Suggest kmalloc_obj family for sizeof allocations
compiler_types: Introduce __flex_counter() and family
slab: Introduce kmalloc_flex() and family
coccinelle: Add kmalloc_objs conversion script

scripts/checkpatch.pl | 39 ++++++--
scripts/coccinelle/api/kmalloc_objs.cocci | 109 ++++++++++++++++++++++
Documentation/process/deprecated.rst | 31 ++++++
include/linux/compiler_types.h | 31 ++++++
include/linux/overflow.h | 42 +++++++++
include/linux/slab.h | 106 +++++++++++++++++++++
6 files changed, 352 insertions(+), 6 deletions(-)
create mode 100644 scripts/coccinelle/api/kmalloc_objs.cocci

--
2.34.1