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Message-ID: <20241029140036.577804-2-kernel@jfarr.cc>
Date: Tue, 29 Oct 2024 15:00:36 +0100
From: Jan Hendrik Farr <kernel@...rr.cc>
To: kees@...nel.org
Cc: nathan@...nel.org,
ojeda@...nel.org,
ndesaulniers@...gle.com,
morbo@...gle.com,
justinstitt@...gle.com,
thorsten.blum@...lux.com,
ardb@...nel.org,
oliver.sang@...el.com,
gustavoars@...nel.org,
kent.overstreet@...ux.dev,
arnd@...db.de,
gregkh@...uxfoundation.org,
akpm@...ux-foundation.org,
tavianator@...ianator.com,
linux-hardening@...r.kernel.org,
llvm@...ts.linux.dev,
linux-kernel@...r.kernel.org,
stable@...r.kernel.org,
kernel@...rr.cc
Subject: [PATCH 1/1] Compiler Attributes: disable __counted_by for clang < 19.1.3
This patch disables __counted_by for clang versions < 19.1.3 because
of the two issues listed below. It does this by introducing
CONFIG_CC_HAS_COUNTED_BY.
1. clang < 19.1.2 has a bug that can lead to __bdos returning 0:
https://github.com/llvm/llvm-project/pull/110497
2. clang < 19.1.3 has a bug that can lead to __bdos being off by 4:
https://github.com/llvm/llvm-project/pull/112636
Fixes: c8248faf3ca2 ("Compiler Attributes: counted_by: Adjust name and identifier expansion")
Cc: stable@...r.kernel.org # 6.6.x: 16c31dd7fdf6: Compiler Attributes: counted_by: bump min gcc version
Cc: stable@...r.kernel.org # 6.6.x: 2993eb7a8d34: Compiler Attributes: counted_by: fixup clang URL
Cc: stable@...r.kernel.org # 6.6.x: 231dc3f0c936: lkdtm/bugs: Improve warning message for compilers without counted_by support
Cc: stable@...r.kernel.org # 6.6.x
Reported-by: Nathan Chancellor <nathan@...nel.org>
Closes: https://lore.kernel.org/all/20240913164630.GA4091534@thelio-3990X/
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202409260949.a1254989-oliver.sang@intel.com
Link: https://lore.kernel.org/all/Zw8iawAF5W2uzGuh@archlinux/T/#m204c09f63c076586a02d194b87dffc7e81b8de7b
Suggested-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Jan Hendrik Farr <kernel@...rr.cc>
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
Tested-by: Nathan Chancellor <nathan@...nel.org>
Reviewed-by: Miguel Ojeda <ojeda@...nel.org>
---
drivers/misc/lkdtm/bugs.c | 2 +-
include/linux/compiler_attributes.h | 13 -------------
include/linux/compiler_types.h | 19 +++++++++++++++++++
init/Kconfig | 9 +++++++++
lib/overflow_kunit.c | 2 +-
5 files changed, 30 insertions(+), 15 deletions(-)
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 62ba01525479..376047beea3d 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -445,7 +445,7 @@ static void lkdtm_FAM_BOUNDS(void)
pr_err("FAIL: survived access of invalid flexible array member index!\n");
- if (!__has_attribute(__counted_by__))
+ if (!IS_ENABLED(CONFIG_CC_HAS_COUNTED_BY))
pr_warn("This is expected since this %s was built with a compiler that does not support __counted_by\n",
lkdtm_kernel_info);
else if (IS_ENABLED(CONFIG_UBSAN_BOUNDS))
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 32284cd26d52..c16d4199bf92 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -94,19 +94,6 @@
# define __copy(symbol)
#endif
-/*
- * Optional: only supported since gcc >= 15
- * Optional: only supported since clang >= 18
- *
- * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
- * clang: https://github.com/llvm/llvm-project/pull/76348
- */
-#if __has_attribute(__counted_by__)
-# define __counted_by(member) __attribute__((__counted_by__(member)))
-#else
-# define __counted_by(member)
-#endif
-
/*
* Optional: not supported by gcc
* Optional: only supported since clang >= 14.0
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 1a957ea2f4fe..639be0f30b45 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -323,6 +323,25 @@ struct ftrace_likely_data {
#define __no_sanitize_or_inline __always_inline
#endif
+/*
+ * Optional: only supported since gcc >= 15
+ * Optional: only supported since clang >= 18
+ *
+ * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
+ * clang: https://github.com/llvm/llvm-project/pull/76348
+ *
+ * __bdos on clang < 19.1.2 can erroneously return 0:
+ * https://github.com/llvm/llvm-project/pull/110497
+ *
+ * __bdos on clang < 19.1.3 can be off by 4:
+ * https://github.com/llvm/llvm-project/pull/112636
+ */
+#ifdef CONFIG_CC_HAS_COUNTED_BY
+# define __counted_by(member) __attribute__((__counted_by__(member)))
+#else
+# define __counted_by(member)
+#endif
+
/*
* Apply __counted_by() when the Endianness matches to increase test coverage.
*/
diff --git a/init/Kconfig b/init/Kconfig
index 530a382ee0fe..92f106cf5572 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -116,6 +116,15 @@ config CC_HAS_ASM_INLINE
config CC_HAS_NO_PROFILE_FN_ATTR
def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
+config CC_HAS_COUNTED_BY
+ # TODO: when gcc 15 is released remove the build test and add
+ # a gcc version check
+ def_bool $(success,echo 'struct flex { int count; int array[] __attribute__((__counted_by__(count))); };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
+ # clang needs to be at least 19.1.3 to avoid __bdos miscalculations
+ # https://github.com/llvm/llvm-project/pull/110497
+ # https://github.com/llvm/llvm-project/pull/112636
+ depends on !(CC_IS_CLANG && CLANG_VERSION < 190103)
+
config PAHOLE_VERSION
int
default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
index 2abc78367dd1..5222c6393f11 100644
--- a/lib/overflow_kunit.c
+++ b/lib/overflow_kunit.c
@@ -1187,7 +1187,7 @@ static void DEFINE_FLEX_test(struct kunit *test)
{
/* Using _RAW_ on a __counted_by struct will initialize "counter" to zero */
DEFINE_RAW_FLEX(struct foo, two_but_zero, array, 2);
-#if __has_attribute(__counted_by__)
+#ifdef CONFIG_CC_HAS_COUNTED_BY
int expected_raw_size = sizeof(struct foo);
#else
int expected_raw_size = sizeof(struct foo) + 2 * sizeof(s16);
--
2.47.0
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