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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id g9-20020a17090a67c900b002465ff5d829sm6599949pjm.13.2023.04.24.09.24.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Apr 2023 09:24:53 -0700 (PDT) Message-ID: <6446ad55.170a0220.c82cd.cedc@mx.google.com> X-Google-Original-Message-ID: <202304240922.@keescook> Date: Mon, 24 Apr 2023 09:24:52 -0700 From: Kees Cook To: Alexander Potapenko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, elver@google.com, dvyukov@google.com, kasan-dev@googlegroups.com, andy@kernel.org, ndesaulniers@google.com, nathan@kernel.org Subject: Re: [PATCH] string: use __builtin_memcpy() in strlcpy/strlcat References: <20230424112313.3408363-1-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230424112313.3408363-1-glider@google.com> X-Stat-Signature: wnn4tqbjpx59e1jke9pawoak4i9k5cuq X-Rspam-User: X-Rspamd-Queue-Id: DE85B4001F X-Rspamd-Server: rspam06 X-HE-Tag: 1682353494-872014 X-HE-Meta: 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 3rHrwnqz rInag8KGy4VOGy4W5AAHCgYa4B3n9TMqbarHzJ+P9OweJj5pX30V9EYOSih5qpM6fLgvkxorIFgTNmKCq+Y0FYzPcPq9raa0WHBJqoTCQIcc7pv0RbH8Iwrpyy10A16BT0YcoD/ma9JpnS5HCA4N5uyYS7S6js2/rID2c0yRf6py6xYCq1aZcQjkUUv8K/8EFjCSOSz2yrr2QgHqvCvxEVcdA6tX2XHF4qGBmTfevi/e/h1rpxfGGkg7SOB/4Q82FNsPvaNJamRF7vQJpVD2WS+ioVkg6aUyTrhbIKeJy2SB89giMWFVlPvLSDng2BDrs5WuYlKpl2WPlaAyVtdvfH63ByjODmk1aIqAswfz+J15qx7ilR/j5j7TT5nporMSlloU4DK1LyHFoquqbYWo+W4Gm93GFZ4rSCNpCXLQZDH0pSkKlB3ozMpe2G2/bvCa8dRfL X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Apr 24, 2023 at 01:23:13PM +0200, Alexander Potapenko wrote: > lib/string.c is built with -ffreestanding, which prevents the compiler > from replacing certain functions with calls to their library versions. > > On the other hand, this also prevents Clang and GCC from instrumenting > calls to memcpy() when building with KASAN, KCSAN or KMSAN: > - KASAN normally replaces memcpy() with __asan_memcpy() with the > additional cc-param,asan-kernel-mem-intrinsic-prefix=1; > - KCSAN and KMSAN replace memcpy() with __tsan_memcpy() and > __msan_memcpy() by default. > > To let the tools catch memory accesses from strlcpy/strlcat, replace > the calls to memcpy() with __builtin_memcpy(), which KASAN, KCSAN and > KMSAN are able to replace even in -ffreestanding mode. > > This preserves the behavior in normal builds (__builtin_memcpy() ends up > being replaced with memcpy()), and does not introduce new instrumentation > in unwanted places, as strlcpy/strlcat are already instrumented. > > Suggested-by: Marco Elver > Signed-off-by: Alexander Potapenko > Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@google.com/ > --- > lib/string.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/lib/string.c b/lib/string.c > index 3d55ef8901068..be26623953d2e 100644 > --- a/lib/string.c > +++ b/lib/string.c > @@ -110,7 +110,7 @@ size_t strlcpy(char *dest, const char *src, size_t size) > > if (size) { > size_t len = (ret >= size) ? size - 1 : ret; > - memcpy(dest, src, len); > + __builtin_memcpy(dest, src, len); > dest[len] = '\0'; > } > return ret; > @@ -260,7 +260,7 @@ size_t strlcat(char *dest, const char *src, size_t count) > count -= dsize; > if (len >= count) > len = count-1; > - memcpy(dest, src, len); > + __builtin_memcpy(dest, src, len); > dest[len] = 0; > return res; I *think* this isn't a problem for CONFIG_FORTIFY, since these will be replaced and checked separately -- but it still seems strange that you need to explicitly use __builtin_memcpy. Does this end up changing fortify coverage? -- Kees Cook