From: Dan Williams <dan.j.williams@intel.com>
To: Kees Cook <keescook@chromium.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Keith Packard <keithp@keithp.com>,
"Gustavo A . R . Silva" <gustavoars@kernel.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Wireless List <linux-wireless@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
Maling list - DRI developers <dri-devel@lists.freedesktop.org>,
linux-staging@lists.linux.dev, linux-block@vger.kernel.org,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 05/63] stddef: Introduce struct_group() helper macro
Date: Wed, 18 Aug 2021 15:35:13 -0700 [thread overview]
Message-ID: <CAPcyv4jU+FhX0e4EXXVzisD5hzsdxK+cyVD3=QuqGOSpE4j-SQ@mail.gmail.com> (raw)
In-Reply-To: <20210818060533.3569517-6-keescook@chromium.org>
On Tue, Aug 17, 2021 at 11:06 PM Kees Cook <keescook@chromium.org> wrote:
>
> Kernel code has a regular need to describe groups of members within a
> structure usually when they need to be copied or initialized separately
> from the rest of the surrounding structure. The generally accepted design
> pattern in C is to use a named sub-struct:
>
> struct foo {
> int one;
> struct {
> int two;
> int three, four;
> } thing;
> int five;
> };
>
> This would allow for traditional references and sizing:
>
> memcpy(&dst.thing, &src.thing, sizeof(dst.thing));
>
> However, doing this would mean that referencing struct members enclosed
> by such named structs would always require including the sub-struct name
> in identifiers:
>
> do_something(dst.thing.three);
>
> This has tended to be quite inflexible, especially when such groupings
> need to be added to established code which causes huge naming churn.
> Three workarounds exist in the kernel for this problem, and each have
> other negative properties.
>
> To avoid the naming churn, there is a design pattern of adding macro
> aliases for the named struct:
>
> #define f_three thing.three
>
> This ends up polluting the global namespace, and makes it difficult to
> search for identifiers.
>
> Another common work-around in kernel code avoids the pollution by avoiding
> the named struct entirely, instead identifying the group's boundaries using
> either a pair of empty anonymous structs of a pair of zero-element arrays:
>
> struct foo {
> int one;
> struct { } start;
> int two;
> int three, four;
> struct { } finish;
> int five;
> };
>
> struct foo {
> int one;
> int start[0];
> int two;
> int three, four;
> int finish[0];
> int five;
> };
>
> This allows code to avoid needing to use a sub-struct named for member
> references within the surrounding structure, but loses the benefits of
> being able to actually use such a struct, making it rather fragile. Using
> these requires open-coded calculation of sizes and offsets. The efforts
> made to avoid common mistakes include lots of comments, or adding various
> BUILD_BUG_ON()s. Such code is left with no way for the compiler to reason
> about the boundaries (e.g. the "start" object looks like it's 0 bytes
> in length), making bounds checking depend on open-coded calculations:
>
> if (length > offsetof(struct foo, finish) -
> offsetof(struct foo, start))
> return -EINVAL;
> memcpy(&dst.start, &src.start, offsetof(struct foo, finish) -
> offsetof(struct foo, start));
>
> However, the vast majority of places in the kernel that operate on
> groups of members do so without any identification of the grouping,
> relying either on comments or implicit knowledge of the struct contents,
> which is even harder for the compiler to reason about, and results in
> even more fragile manual sizing, usually depending on member locations
> outside of the region (e.g. to copy "two" and "three", use the start of
> "four" to find the size):
>
> BUILD_BUG_ON((offsetof(struct foo, four) <
> offsetof(struct foo, two)) ||
> (offsetof(struct foo, four) <
> offsetof(struct foo, three));
> if (length > offsetof(struct foo, four) -
> offsetof(struct foo, two))
> return -EINVAL;
> memcpy(&dst.two, &src.two, length);
>
> In order to have a regular programmatic way to describe a struct
> region that can be used for references and sizing, can be examined for
> bounds checking, avoids forcing the use of intermediate identifiers,
> and avoids polluting the global namespace, introduce the struct_group()
> macro. This macro wraps the member declarations to create an anonymous
> union of an anonymous struct (no intermediate name) and a named struct
> (for references and sizing):
>
> struct foo {
> int one;
> struct_group(thing,
> int two;
> int three, four;
> );
> int five;
> };
>
> if (length > sizeof(src.thing))
> return -EINVAL;
> memcpy(&dst.thing, &src.thing, length);
> do_something(dst.three);
>
> There are some rare cases where the resulting struct_group() needs
> attributes added, so struct_group_attr() is also introduced to allow
> for specifying struct attributes (e.g. __align(x) or __packed).
> Additionally, there are places where such declarations would like to
> have the struct be typed, so struct_group_typed() is added.
>
> Given there is a need for a handful of UAPI uses too, the underlying
> __struct_group() macro has been defined in UAPI so it can be used there
> too.
>
> Co-developed-by: Keith Packard <keithp@keithp.com>
> Signed-off-by: Keith Packard <keithp@keithp.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> Link: https://lore.kernel.org/lkml/20210728023217.GC35706@embeddedor
> Enhanced-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Link: https://lore.kernel.org/lkml/41183a98-bdb9-4ad6-7eab-5a7292a6df84@rasmusvillemoes.dk
> Enhanced-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
next prev parent reply other threads:[~2021-08-18 22:35 UTC|newest]
Thread overview: 116+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 6:04 [PATCH v2 00/63] Introduce strict memcpy() bounds checking Kees Cook
2021-08-18 6:04 ` [PATCH v2 01/63] ipw2x00: Avoid field-overflowing memcpy() Kees Cook
2021-08-18 6:04 ` [PATCH v2 02/63] net/mlx5e: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 03/63] rpmsg: glink: Replace strncpy() with strscpy_pad() Kees Cook
2021-08-18 6:04 ` [PATCH v2 04/63] pcmcia: ray_cs: Split memcpy() to avoid bounds check warning Kees Cook
2021-08-18 6:04 ` [PATCH v2 05/63] stddef: Introduce struct_group() helper macro Kees Cook
2021-08-18 22:35 ` Dan Williams [this message]
2021-08-18 6:04 ` [PATCH v2 06/63] cxl/core: Replace unions with struct_group() Kees Cook
2021-08-18 22:36 ` Dan Williams
2021-08-18 6:04 ` [PATCH v2 07/63] skbuff: Switch structure bounds to struct_group() Kees Cook
2021-09-01 13:46 ` Jason A. Donenfeld
2021-08-18 6:04 ` [PATCH v2 08/63] bnxt_en: Use struct_group_attr() for memcpy() region Kees Cook
2021-08-18 6:04 ` [PATCH v2 09/63] mwl8k: Use struct_group() " Kees Cook
2021-08-18 6:04 ` [PATCH v2 10/63] libertas: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 11/63] libertas_tf: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 12/63] thermal: intel: int340x_thermal: " Kees Cook
2021-11-23 13:19 ` Rafael J. Wysocki
2021-11-23 23:53 ` Srinivas Pandruvada
2021-11-24 13:33 ` Rafael J. Wysocki
2021-08-18 6:04 ` [PATCH v2 13/63] iommu/amd: " Kees Cook
2021-08-18 11:34 ` Joerg Roedel
2021-08-18 6:04 ` [PATCH v2 14/63] cxgb3: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 15/63] intersil: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 16/63] cxgb4: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 17/63] bnx2x: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 18/63] drm/amd/pm: " Kees Cook
2021-08-18 11:42 ` Lazar, Lijo
2021-08-18 23:59 ` Kees Cook
2021-08-19 5:03 ` Lazar, Lijo
2021-08-19 19:58 ` Kees Cook
2021-08-18 6:04 ` [PATCH v2 19/63] staging: wlan-ng: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 20/63] drm/mga/mga_ioc32: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 21/63] net/mlx5e: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 22/63] HID: cp2112: " Kees Cook
2021-08-20 13:01 ` Jiri Kosina
2021-08-20 15:48 ` Kees Cook
2021-08-18 6:04 ` [PATCH v2 23/63] media: omap3isp: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 24/63] sata_fsl: " Kees Cook
2021-08-18 6:04 ` [PATCH v2 25/63] compiler_types.h: Remove __compiletime_object_size() Kees Cook
2021-08-18 13:02 ` Miguel Ojeda
2021-08-18 6:04 ` [PATCH v2 26/63] lib/string: Move helper functions out of string.c Kees Cook
2021-08-18 9:35 ` Andy Shevchenko
2021-08-18 6:04 ` [PATCH v2 27/63] fortify: Move remaining fortify helpers into fortify-string.h Kees Cook
2021-08-18 19:05 ` Francis Laniel
2021-08-18 6:04 ` [PATCH v2 28/63] fortify: Explicitly disable Clang support Kees Cook
2021-08-18 6:04 ` [PATCH v2 29/63] fortify: Fix dropped strcpy() compile-time write overflow check Kees Cook
2021-08-18 6:05 ` [PATCH v2 30/63] fortify: Prepare to improve strnlen() and strlen() warnings Kees Cook
2021-08-18 6:05 ` [PATCH v2 31/63] fortify: Allow strlen() and strnlen() to pass compile-time known lengths Kees Cook
2021-08-18 6:05 ` [PATCH v2 32/63] fortify: Add compile-time FORTIFY_SOURCE tests Kees Cook
2021-08-18 6:05 ` [PATCH v2 33/63] lib: Introduce CONFIG_TEST_MEMCPY Kees Cook
2021-08-18 6:05 ` [PATCH v2 34/63] fortify: Detect struct member overflows in memcpy() at compile-time Kees Cook
2021-08-18 6:05 ` [PATCH v2 35/63] fortify: Detect struct member overflows in memmove() " Kees Cook
2021-08-18 6:05 ` [PATCH v2 36/63] scsi: ibmvscsi: Avoid multi-field memset() overflow by aiming at srp Kees Cook
2021-08-18 6:05 ` [PATCH v2 37/63] string.h: Introduce memset_after() for wiping trailing members/padding Kees Cook
2021-08-18 6:05 ` [PATCH v2 38/63] xfrm: Use memset_after() to clear padding Kees Cook
2021-08-18 6:05 ` [PATCH v2 39/63] ipv6: Use memset_after() to zero rt6_info Kees Cook
2021-08-18 6:05 ` [PATCH v2 40/63] netfilter: conntrack: Use memset_startat() to zero struct nf_conn Kees Cook
2021-08-18 6:05 ` [PATCH v2 41/63] net: 802: Use memset_startat() to clear struct fields Kees Cook
2021-08-18 6:05 ` [PATCH v2 42/63] net: dccp: Use memset_startat() for TP zeroing Kees Cook
2021-08-18 6:05 ` [PATCH v2 43/63] net: qede: Use memset_startat() for counters Kees Cook
2021-08-18 6:05 ` [PATCH v2 44/63] mac80211: Use memset_after() to clear tx status Kees Cook
2021-08-18 7:08 ` Johannes Berg
2021-08-18 8:06 ` Johannes Berg
2021-08-18 9:05 ` Kees Cook
2021-08-18 6:05 ` [PATCH v2 45/63] ath11k: Use memset_startat() for clearing queue descriptors Kees Cook
2021-08-19 13:19 ` Kalle Valo
2021-08-19 16:25 ` Kees Cook
2021-08-21 10:17 ` Kalle Valo
2021-08-22 8:11 ` Kees Cook
2021-08-18 6:05 ` [PATCH v2 46/63] iw_cxgb4: Use memset_startat() for cpl_t5_pass_accept_rpl Kees Cook
2021-08-18 6:05 ` [PATCH v2 47/63] intel_th: msu: Use memset_startat() for clearing hw header Kees Cook
2021-08-24 7:38 ` Alexander Shishkin
2021-08-18 6:05 ` [PATCH v2 48/63] IB/mthca: Use memset_startat() for clearing mpt_entry Kees Cook
2021-08-18 6:05 ` [PATCH v2 49/63] btrfs: Use memset_startat() to clear end of struct Kees Cook
2021-08-18 6:35 ` Nikolay Borisov
2021-08-18 9:28 ` David Sterba
2021-08-18 6:05 ` [PATCH v2 50/63] tracing: Use memset_startat() to zero struct trace_iterator Kees Cook
2021-08-18 13:33 ` Steven Rostedt
2021-08-18 16:21 ` Kees Cook
2021-08-18 6:05 ` [PATCH v2 51/63] drbd: Use struct_group() to zero algs Kees Cook
2021-08-18 6:05 ` [PATCH v2 52/63] cm4000_cs: Use struct_group() to zero struct cm4000_dev region Kees Cook
2021-08-18 6:05 ` [PATCH v2 53/63] KVM: x86: Use struct_group() to zero decode cache Kees Cook
2021-08-18 15:11 ` Sean Christopherson
2021-08-18 16:23 ` Kees Cook
2021-08-18 22:53 ` Sean Christopherson
2021-08-18 23:06 ` Kees Cook
2021-08-18 6:05 ` [PATCH v2 54/63] dm integrity: Use struct_group() to zero struct journal_sector Kees Cook
2021-08-18 6:05 ` [PATCH v2 55/63] HID: roccat: Use struct_group() to zero kone_mouse_event Kees Cook
2021-08-20 13:02 ` Jiri Kosina
[not found] ` <CAJr-aD=6-g7VRw2Hw0dhs+RrtA=Tago5r6Dukfw_gGPB0YYKOQ@mail.gmail.com>
2021-08-20 15:27 ` Jiri Kosina
2021-08-20 15:49 ` Kees Cook
2021-08-20 15:57 ` Kees Cook
2021-08-20 16:11 ` Jiri Kosina
2021-08-18 6:05 ` [PATCH v2 56/63] RDMA/mlx5: Use struct_group() to zero struct mlx5_ib_mr Kees Cook
2021-08-19 12:27 ` Jason Gunthorpe
2021-08-19 16:19 ` Kees Cook
2021-08-19 16:47 ` Jason Gunthorpe
2021-08-19 18:14 ` Kees Cook
2021-08-20 12:34 ` Jason Gunthorpe
2021-08-20 15:56 ` Kees Cook
2021-08-18 6:05 ` [PATCH v2 57/63] powerpc/signal32: Use struct_group() to zero spe regs Kees Cook
2021-08-20 7:49 ` Michael Ellerman
2021-08-20 7:53 ` Christophe Leroy
2021-08-20 12:13 ` Michael Ellerman
2021-08-20 15:55 ` Kees Cook
2021-08-23 4:55 ` Michael Ellerman
2021-08-18 6:05 ` [PATCH v2 58/63] ethtool: stats: Use struct_group() to clear all stats at once Kees Cook
2021-08-18 6:05 ` [PATCH v2 59/63] can: flexcan: Use struct_group() to zero struct flexcan_regs regions Kees Cook
2021-08-18 6:26 ` Marc Kleine-Budde
2021-08-18 6:05 ` [PATCH v2 60/63] net/af_iucv: Use struct_group() to zero struct iucv_sock region Kees Cook
2021-09-09 6:14 ` Karsten Graul
2021-08-18 6:05 ` [PATCH v2 61/63] powerpc: Split memset() to avoid multi-field overflow Kees Cook
2021-08-18 6:42 ` Christophe Leroy
2021-08-18 22:30 ` Kees Cook
2021-08-18 6:05 ` [PATCH v2 62/63] fortify: Detect struct member overflows in memset() at compile-time Kees Cook
2021-08-18 6:05 ` [PATCH v2 63/63] fortify: Work around Clang inlining bugs Kees Cook
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