linux-hardening - [PATCH net-next v2 1/3] compiler_types: add Endianness-dependent __counted_by

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Date: Wed, 27 Mar 2024 15:22:39 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>,
	Kees Cook <keescook@...omium.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Simon Horman <horms@...nel.org>,
	nex.sw.ncis.osdt.itp.upstreaming@...el.com,
	intel-wired-lan@...ts.osuosl.org,
	linux-hardening@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net-next v2 1/3] compiler_types: add Endianness-dependent __counted_by_{le,be}

Some structures contain flexible arrays at the end and the counter for
them, but the counter has explicit Endianness and thus __counted_by()
can't be used directly.

To increase test coverage for potential problems without breaking
anything, introduce __counted_by_{le,be}() defined depending on
platform's Endianness to either __counted_by() when applicable or noop
otherwise.
Maybe it would be a good idea to introduce such attributes on compiler
level if possible, but for now let's stop on what we have.

Acked-by: Kees Cook <keescook@...omium.org>
Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
---
 Documentation/conf.py          |  2 ++
 scripts/kernel-doc             |  1 +
 include/linux/compiler_types.h | 11 +++++++++++
 3 files changed, 14 insertions(+)

diff --git a/Documentation/conf.py b/Documentation/conf.py
index d148f3e8dd57..0c2205d536b3 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -75,6 +75,8 @@ if major >= 3:
             "__rcu",
             "__user",
             "__force",
+            "__counted_by_le",
+            "__counted_by_be",
 
             # include/linux/compiler_attributes.h:
             "__alias",
diff --git a/scripts/kernel-doc b/scripts/kernel-doc
index 967f1abb0edb..1474e95dbe4f 100755
--- a/scripts/kernel-doc
+++ b/scripts/kernel-doc
@@ -1143,6 +1143,7 @@ sub dump_struct($$) {
         $members =~ s/\s*$attribute/ /gi;
         $members =~ s/\s*__aligned\s*\([^;]*\)/ /gos;
         $members =~ s/\s*__counted_by\s*\([^;]*\)/ /gos;
+        $members =~ s/\s*__counted_by_(le|be)\s*\([^;]*\)/ /gos;
         $members =~ s/\s*__packed\s*/ /gos;
         $members =~ s/\s*CRYPTO_MINALIGN_ATTR/ /gos;
         $members =~ s/\s*____cacheline_aligned_in_smp/ /gos;
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 2abaa3a825a9..a29ba6ef1e27 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -282,6 +282,17 @@ struct ftrace_likely_data {
 #define __no_sanitize_or_inline __always_inline
 #endif
 
+/*
+ * Apply __counted_by() when the Endianness matches to increase test coverage.
+ */
+#ifdef __LITTLE_ENDIAN
+#define __counted_by_le(member)	__counted_by(member)
+#define __counted_by_be(member)
+#else
+#define __counted_by_le(member)
+#define __counted_by_be(member)	__counted_by(member)
+#endif
+
 /* Do not trap wrapping arithmetic within an annotated function. */
 #ifdef CONFIG_UBSAN_SIGNED_WRAP
 # define __signed_wrap __attribute__((no_sanitize("signed-integer-overflow")))
-- 
2.44.0