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Kees Cook 05a940656e slab: Introduce kmalloc_size_roundup()
In the effort to help the compiler reason about buffer sizes, the
__alloc_size attribute was added to allocators. This improves the scope
of the compiler's ability to apply CONFIG_UBSAN_BOUNDS and (in the near
future) CONFIG_FORTIFY_SOURCE. For most allocations, this works well,
as the vast majority of callers are not expecting to use more memory
than what they asked for.

There is, however, one common exception to this: anticipatory resizing
of kmalloc allocations. These cases all use ksize() to determine the
actual bucket size of a given allocation (e.g. 128 when 126 was asked
for). This comes in two styles in the kernel:

1) An allocation has been determined to be too small, and needs to be
   resized. Instead of the caller choosing its own next best size, it
   wants to minimize the number of calls to krealloc(), so it just uses
   ksize() plus some additional bytes, forcing the realloc into the next
   bucket size, from which it can learn how large it is now. For example:

	data = krealloc(data, ksize(data) + 1, gfp);
	data_len = ksize(data);

2) The minimum size of an allocation is calculated, but since it may
   grow in the future, just use all the space available in the chosen
   bucket immediately, to avoid needing to reallocate later. A good
   example of this is skbuff's allocators:

	data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc);
	...
	/* kmalloc(size) might give us more room than requested.
	 * Put skb_shared_info exactly at the end of allocated zone,
	 * to allow max possible filling before reallocation.
	 */
	osize = ksize(data);
        size = SKB_WITH_OVERHEAD(osize);

In both cases, the "how much was actually allocated?" question is answered
_after_ the allocation, where the compiler hinting is not in an easy place
to make the association any more. This mismatch between the compiler's
view of the buffer length and the code's intention about how much it is
going to actually use has already caused problems[1]. It is possible to
fix this by reordering the use of the "actual size" information.

We can serve the needs of users of ksize() and still have accurate buffer
length hinting for the compiler by doing the bucket size calculation
_before_ the allocation. Code can instead ask "how large an allocation
would I get for a given size?".

Introduce kmalloc_size_roundup(), to serve this function so we can start
replacing the "anticipatory resizing" uses of ksize().

[1] https://github.com/ClangBuiltLinux/linux/issues/1599
    https://github.com/KSPP/linux/issues/183

[ vbabka@suse.cz: add SLOB version ]

Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
2022-09-29 11:10:34 +02:00
arch Misc irqchip fixes: LoongArch driver fixes and a Hyper-V IOMMU fix. 2022-08-21 15:09:55 -07:00
block block-6.0-2022-08-19 2022-08-20 10:17:05 -07:00
certs Kbuild updates for v5.20 2022-08-10 10:40:41 -07:00
crypto crypto: blake2b: effectively disable frame size warning 2022-08-10 17:59:11 -07:00
Documentation asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
drivers Misc irqchip fixes: LoongArch driver fixes and a Hyper-V IOMMU fix. 2022-08-21 15:09:55 -07:00
fs 5 cifs/smb3 fixes, one for stable 2022-08-21 10:21:16 -07:00
include slab: Introduce kmalloc_size_roundup() 2022-09-29 11:10:34 +02:00
init asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
io_uring io_uring/net: use right helpers for async_data 2022-08-18 07:27:20 -06:00
ipc Updates to various subsystems which I help look after. lib, ocfs2, 2022-08-07 10:03:24 -07:00
kernel Various fixes for tracing: 2022-08-21 14:49:42 -07:00
lib lib/cpumask: drop always-true preprocessor guard 2022-08-15 11:00:44 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm slab: Introduce kmalloc_size_roundup() 2022-09-29 11:10:34 +02:00
net tcp: handle pure FIN case correctly 2022-08-18 11:04:56 -07:00
samples Tracing updates for 5.20 / 6.0 2022-08-05 09:41:12 -07:00
scripts asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
security hardening fixes for v6.0-rc2 2022-08-19 13:56:14 -07:00
sound sound fixes for 6.0-rc2 2022-08-19 09:46:11 -07:00
tools asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt KVM: Drop unnecessary initialization of "ops" in kvm_ioctl_create_device() 2022-08-19 04:05:43 -04:00
.clang-format PCI/DOE: Add DOE mailbox support functions 2022-07-19 15:38:04 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap Updates to various subsystems which I help look after. lib, ocfs2, 2022-08-07 10:03:24 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS drm for 5.20/6.0 2022-08-03 19:52:08 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS 5 cifs/smb3 fixes, one for stable 2022-08-21 10:21:16 -07:00
Makefile Linux 6.0-rc2 2022-08-21 17:32:54 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.