From: Ian Rogers <irogers@google.com>
To: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: Ian Rogers <irogers@google.com>
Subject: [PATCH] libbpf hashmap: Fix undefined behavior in hash_bits
Date: Thu, 29 Oct 2020 09:09:38 -0700 [thread overview]
Message-ID: <20201029160938.154084-1-irogers@google.com> (raw)
If bits is 0, the case when the map is empty, then the >> is the size of
the register which is undefined behavior - on x86 it is the same as a
shift by 0. Fix by handling the 0 case explicitly when running with
address sanitizer.
A variant of this patch was posted previously as:
https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/lib/bpf/hashmap.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
index d9b385fe808c..27d0556527d3 100644
--- a/tools/lib/bpf/hashmap.h
+++ b/tools/lib/bpf/hashmap.h
@@ -12,9 +12,23 @@
#include <stddef.h>
#include <limits.h>
+#ifdef __has_feature
+#define HAVE_FEATURE(f) __has_feature(f)
+#else
+#define HAVE_FEATURE(f) 0
+#endif
+
static inline size_t hash_bits(size_t h, int bits)
{
/* shuffle bits and return requested number of upper bits */
+#if defined(ADDRESS_SANITIZER) || HAVE_FEATURE(address_sanitizer)
+ /*
+ * If the requested bits == 0 avoid undefined behavior from a
+ * greater-than bit width shift right (aka invalid-shift-exponent).
+ */
+ if (bits == 0)
+ return -1;
+#endif
#if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__)
/* LP64 case */
return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits);
--
2.29.1.341.ge80a0c044ae-goog
next reply other threads:[~2020-10-29 16:09 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-29 16:09 Ian Rogers [this message]
2020-10-29 17:45 ` [PATCH] libbpf hashmap: Fix undefined behavior in hash_bits Song Liu
2020-10-29 19:37 ` Ian Rogers
2020-10-29 20:16 ` Andrii Nakryiko
2020-10-29 20:58 ` Ian Rogers
-- strict thread matches above, loose matches on Subject: below --
2020-05-08 6:39 [PATCH] libbpf hashmap: fix " Ian Rogers
2020-05-08 7:11 ` Andrii Nakryiko
2020-05-08 7:21 ` Ian Rogers
2020-05-08 18:04 ` Andrii Nakryiko
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