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* string.h: Introduce memset_startat() for wiping trailing members and paddingKees Cook2021-10-181-0/+11
| | | | | | | | | | | | | | | | | | | | | | | A common idiom in kernel code is to wipe the contents of a structure starting from a given member. These open-coded cases are usually difficult to read and very sensitive to struct layout changes. Like memset_after(), introduce a new helper, memset_startat() that takes the target struct instance, the byte to write, and the member name where zeroing should start. Note that this doesn't zero padding preceding the target member. For those cases, memset_after() should be used on the preceding member. Cc: Steffen Klassert <steffen.klassert@secunet.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: "David S. Miller" <davem@davemloft.net> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Francis Laniel <laniel_francis@privacyrequired.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Daniel Axtens <dja@axtens.net> Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org>
* string.h: Introduce memset_after() for wiping trailing members/paddingKees Cook2021-10-181-0/+13
| | | | | | | | | | | | | | | | | | | | 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. Cc: Steffen Klassert <steffen.klassert@secunet.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: "David S. Miller" <davem@davemloft.net> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Francis Laniel <laniel_francis@privacyrequired.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Daniel Axtens <dja@axtens.net> Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org>
* lib: Introduce CONFIG_MEMCPY_KUNIT_TESTKees Cook2021-10-181-0/+265
Before changing anything about memcpy(), memmove(), and memset(), add run-time tests to check basic behaviors for any regressions. Signed-off-by: Kees Cook <keescook@chromium.org>