From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
Kees Cook <keescook@chromium.org>
Subject: [PATCH] efi: Replace zero-length array and use struct_size() helper
Date: Wed, 27 May 2020 12:14:25 -0500 [thread overview]
Message-ID: <20200527171425.GA4053@embeddedor> (raw)
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
Lastly, make use of the sizeof_field() helper instead of an open-coded
version.
This issue was found with the help of Coccinelle and audited _manually_.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
drivers/firmware/efi/efi.c | 3 ++-
include/linux/efi.h | 7 ++-----
2 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 7f1657b6c30df..edc5d36caf54e 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -622,7 +622,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
rsv = (void *)(p + prsv % PAGE_SIZE);
/* reserve the entry itself */
- memblock_reserve(prsv, EFI_MEMRESERVE_SIZE(rsv->size));
+ memblock_reserve(prsv,
+ struct_size(rsv, entry, rsv->size));
for (i = 0; i < atomic_read(&rsv->count); i++) {
memblock_reserve(rsv->entry[i].base,
diff --git a/include/linux/efi.h b/include/linux/efi.h
index c45ac969ea4eb..328cc52a5fd45 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {
struct {
phys_addr_t base;
phys_addr_t size;
- } entry[0];
+ } entry[];
};
-#define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
- (count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
-
#define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
- / sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
+ / sizeof_field(struct linux_efi_memreserve, entry[0]))
void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size);
--
2.26.2
next reply other threads:[~2020-05-27 17:09 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-27 17:14 Gustavo A. R. Silva [this message]
2020-05-29 8:31 ` [PATCH] efi: Replace zero-length array and use struct_size() helper Kees Cook
2020-05-29 17:37 ` Gustavo A. R. Silva
2020-06-15 10:00 ` Ard Biesheuvel
2020-06-19 16:46 ` [tip: efi/urgent] " tip-bot2 for Gustavo A. R. Silva
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200527171425.GA4053@embeddedor \
--to=gustavoars@kernel.org \
--cc=ardb@kernel.org \
--cc=gustavo@embeddedor.com \
--cc=keescook@chromium.org \
--cc=linux-efi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).