From: Kees Cook <keescook@chromium.org>
To: linux-kernel@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Daniel Micay <danielmicay@gmail.com>,
Francis Laniel <laniel_francis@privacyrequired.com>,
Bart Van Assche <bvanassche@acm.org>,
David Gow <davidgow@google.com>,
linux-mm@kvack.org, clang-built-linux@googlegroups.com,
linux-hardening@vger.kernel.org
Subject: [PATCH for-next 22/25] string.h: Introduce memset_after() for wiping trailing members/padding
Date: Sun, 22 Aug 2021 00:51:19 -0700 [thread overview]
Message-ID: <20210822075122.864511-23-keescook@chromium.org> (raw)
In-Reply-To: <20210822075122.864511-1-keescook@chromium.org>
A common idiom in kernel code is to wipe the contents of a structure
after a given member. This is especially useful in places where there is
trailing padding. These open-coded cases are usually difficult to read
and very sensitive to struct layout changes. Introduce a new helper,
memset_after() that takes the target struct instance, the byte to write,
and the member name after which the zeroing should start.
Additionally adds memset_startat() for wiping trailing members _starting_
at a specific member instead of after a member, which is more readable
in certain circumstances, but doesn't include any preceding padding.
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/string.h | 17 +++++++++++++++++
lib/test_memcpy.c | 13 +++++++++++++
2 files changed, 30 insertions(+)
diff --git a/include/linux/string.h b/include/linux/string.h
index 9473f81b9db2..d593de2635ba 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -271,6 +271,23 @@ static inline void memcpy_and_pad(void *dest, size_t dest_len,
memcpy(dest, src, dest_len);
}
+/**
+ * memset_after - Set a value after a struct member to the end of a struct
+ *
+ * @obj: Address of target struct instance
+ * @v: Byte value to repeatedly write
+ * @member: after which struct member to start writing bytes
+ *
+ * This is good for clearing padding following the given member.
+ */
+#define memset_after(obj, v, member) \
+({ \
+ u8 *__ptr = (u8 *)(obj); \
+ typeof(v) __val = (v); \
+ memset(__ptr + offsetofend(typeof(*(obj)), member), __val, \
+ sizeof(*(obj)) - offsetofend(typeof(*(obj)), member)); \
+})
+
/**
* str_has_prefix - Test if a string has a given prefix
* @str: The string to test
diff --git a/lib/test_memcpy.c b/lib/test_memcpy.c
index ec546cec883e..3b485de8c885 100644
--- a/lib/test_memcpy.c
+++ b/lib/test_memcpy.c
@@ -215,6 +215,13 @@ static void memset_test(struct kunit *test)
0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
},
};
+ struct some_bytes after = {
+ .data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x72,
+ 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72,
+ 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72,
+ 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72,
+ },
+ };
struct some_bytes dest = { };
int count, value;
u8 *ptr;
@@ -245,6 +252,12 @@ static void memset_test(struct kunit *test)
ptr += 8;
memset(ptr++, value++, count++);
compare("argument side-effects", dest, three);
+
+ /* Verify memset_after() */
+ dest = control;
+ memset_after(&dest, 0x72, three);
+ compare("memset_after()", dest, after);
+
#undef TEST_OP
}
--
2.30.2
next prev parent reply other threads:[~2021-08-22 7:56 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-22 7:50 [PATCH for-next 00/25] Prepare for better FORTIFY_SOURCE Kees Cook
2021-08-22 7:50 ` [PATCH for-next 01/25] scsi: ibmvscsi: Avoid multi-field memset() overflow by aiming at srp Kees Cook
2021-08-22 7:50 ` [PATCH for-next 02/25] powerpc: Split memset() to avoid multi-field overflow Kees Cook
2021-08-22 7:51 ` [PATCH for-next 03/25] stddef: Fix kerndoc for sizeof_field() and offsetofend() Kees Cook
2021-08-22 7:51 ` [PATCH for-next 04/25] stddef: Introduce struct_group() helper macro Kees Cook
2021-08-22 7:51 ` [PATCH for-next 05/25] cxl/core: Replace unions with struct_group() Kees Cook
2021-08-22 7:51 ` [PATCH for-next 06/25] bnxt_en: Use struct_group_attr() for memcpy() region Kees Cook
2021-08-22 7:51 ` [PATCH for-next 07/25] iommu/amd: Use struct_group() " Kees Cook
2021-08-22 7:51 ` [PATCH for-next 08/25] drm/mga/mga_ioc32: " Kees Cook
2021-08-22 7:51 ` [PATCH for-next 09/25] HID: cp2112: " Kees Cook
2021-08-22 7:51 ` [PATCH for-next 10/25] HID: roccat: Use struct_group() to zero kone_mouse_event Kees Cook
2021-08-22 7:51 ` [PATCH for-next 11/25] can: flexcan: Use struct_group() to zero struct flexcan_regs regions Kees Cook
2021-08-22 7:51 ` [PATCH for-next 12/25] cm4000_cs: Use struct_group() to zero struct cm4000_dev region Kees Cook
2021-08-22 7:51 ` [PATCH for-next 13/25] compiler_types.h: Remove __compiletime_object_size() Kees Cook
2021-08-23 6:43 ` Rasmus Villemoes
2021-08-25 19:43 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 14/25] lib/string: Move helper functions out of string.c Kees Cook
2021-08-25 21:48 ` Nick Desaulniers
2021-08-26 2:47 ` Kees Cook
2021-08-26 18:08 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 15/25] fortify: Move remaining fortify helpers into fortify-string.h Kees Cook
2021-08-25 21:59 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 16/25] fortify: Explicitly disable Clang support Kees Cook
2021-08-25 19:41 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 17/25] fortify: Fix dropped strcpy() compile-time write overflow check Kees Cook
2021-08-25 21:55 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 18/25] fortify: Prepare to improve strnlen() and strlen() warnings Kees Cook
2021-08-25 22:01 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 19/25] fortify: Allow strlen() and strnlen() to pass compile-time known lengths Kees Cook
2021-08-25 22:05 ` Nick Desaulniers
2021-08-26 2:56 ` Kees Cook
2021-08-26 18:02 ` Nick Desaulniers
2021-08-22 7:51 ` [PATCH for-next 20/25] fortify: Add compile-time FORTIFY_SOURCE tests Kees Cook
2021-08-22 7:51 ` [PATCH for-next 21/25] lib: Introduce CONFIG_TEST_MEMCPY Kees Cook
2021-08-24 7:00 ` David Gow
2021-08-25 2:32 ` Kees Cook
2021-10-18 15:46 ` Arnd Bergmann
2021-10-18 19:28 ` Kees Cook
2021-08-22 7:51 ` Kees Cook [this message]
2021-08-22 7:51 ` [PATCH for-next 23/25] xfrm: Use memset_after() to clear padding Kees Cook
2021-08-22 7:51 ` [PATCH for-next 24/25] string.h: Introduce memset_startat() for wiping trailing members and padding Kees Cook
2021-08-22 7:51 ` [PATCH for-next 25/25] btrfs: Use memset_startat() to clear end of struct Kees Cook
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