From: Nick Desaulniers <ndesaulniers@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev, Jiri Kosina <jikos@kernel.org>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
linux-input@vger.kernel.org,
Masahiro Yamada <masahiroy@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>
Subject: [PATCH 2/3] fortify: cosmetic cleanups to __compiletime_strlen
Date: Tue, 30 Aug 2022 13:53:08 -0700 [thread overview]
Message-ID: <20220830205309.312864-3-ndesaulniers@google.com> (raw)
In-Reply-To: <20220830205309.312864-1-ndesaulniers@google.com>
Two things I noticed in __compiletime_strlen:
1. A temporary, __p, is created+used to avoid repeated side effects from
multiple evaluation of the macro parameter, but the macro parameter
was being used accidentally in __builtin_object_size.
2. The temporary has a curious signedness and const-less qualification.
Just use __auto_type.
3. (size_t)-1 is perhaps more readable as -1UL.
4. __p_size == -1UL when __builtin_object_size can't evaluate the
object size at compile time. We could just reuse __ret and use one
less variable here.
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
include/linux/fortify-string.h | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index c5adad596a3f..aaf73575050f 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -22,11 +22,10 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("
#define __compiletime_strlen(p) \
({ \
- unsigned char *__p = (unsigned char *)(p); \
- size_t __ret = (size_t)-1; \
- size_t __p_size = __object_size(p, 1); \
- if (__p_size != (size_t)-1) { \
- size_t __p_len = __p_size - 1; \
+ __auto_type __p = (p); \
+ size_t __ret = __object_size(__p, 1); \
+ if (__ret != -1UL) { \
+ size_t __p_len = __ret - 1; \
if (__builtin_constant_p(__p[__p_len]) && \
__p[__p_len] == '\0') \
__ret = __builtin_strlen(__p); \
--
2.37.2.672.g94769d06f0-goog
next prev parent reply other threads:[~2022-08-30 20:53 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-30 20:53 [PATCH 0/3] Fix FORTIFY=y UBSAN_LOCAL_BOUNDS=y Nick Desaulniers
2022-08-30 20:53 ` [PATCH 1/3] fortify: use __builtin_dynamic_object_size in __compiletime_strlen Nick Desaulniers
2022-08-31 18:34 ` Kees Cook
2022-08-30 20:53 ` Nick Desaulniers [this message]
2022-08-31 13:13 ` [PATCH 2/3] fortify: cosmetic cleanups to __compiletime_strlen kernel test robot
2022-08-31 19:06 ` Kees Cook
2022-08-30 20:53 ` [PATCH 3/3] HID: avoid runtime call to strlen Nick Desaulniers
2022-08-31 6:05 ` Greg KH
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