From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy1-f201.google.com (mail-dy1-f201.google.com [74.125.82.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5B3C62D9EE4 for ; Sat, 21 Mar 2026 02:45:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774061110; cv=none; b=PyIEGR6ZPnzt5K/TFe/poF1ZKsQH6z60s1Ey4AqaFRsbXJS6uatSdvSXPclj1/rrAkKfA0HA2Ja93bRfmQ/Y9fk+lHCUm2I3LIB4dDWbUF1izTZL6C5+4u3IFFlc1a7G4LdikAoHmgqF0MH1ilyAL9YFpNK25pc/QBX4EAxm054= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774061110; c=relaxed/simple; bh=Q6p/PKASAUnOEbKLfuwx+b19UcjF5du/pBhWbx4ayKA=; h=Date:Mime-Version:Message-ID:Subject:From:To:Content-Type; b=Ce857P7rF5R74oaB6bkYaoH4uAzGvWrvSUNOTMaM0OtrJ13PSAEHzOyhvB92fJsi2MKnGhKjEQHW+0Jmo50t3KLqKlSBhnC0xwBXuePABq1vTxuixpJ3mvPZ9TNfT+g07SBl80OH2smeQwwYbvV8xtrDKelAqh/wW3JaoOqGQl8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=aG1bR20n; arc=none smtp.client-ip=74.125.82.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="aG1bR20n" Received: by mail-dy1-f201.google.com with SMTP id 5a478bee46e88-2c105e5ac70so1224710eec.0 for ; Fri, 20 Mar 2026 19:45:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1774061107; x=1774665907; darn=vger.kernel.org; h=to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=g+THnNIhXb4I1Hax0SNl1UEHbEI4ZOIHd6uYzFFXr4o=; b=aG1bR20nCZIRehSZhaVDcIJqVN36sfGAM5yO0vLJcQghaohoeDAhFndRenY5Aj/THC TcvTzo1irXYYT8kQYrSQHgmu+UGPviPca8HR7cj4eV4ik+tbxc3EnY0W8FKmpoPlqXSb wo/pw6n1oBIAhxsRJRzMZ3HDiG+d6OK1dlkIHmzTwyUpYpdOq0L/n3+DcIFZUo3ExDgo M6b9l7TKeoSKazPImU5MAluOFl6HqATQjBWZMv2YLyJ0b6MrGiK862f3sNtxOYcrCOf5 oFyIFwSUsKhfRvR2WWEDm6TZ8Pclm0LCDDLyktWKiO++c/MGZ8AYBYuRLjlXy2qZJF8/ Nr7Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774061107; x=1774665907; h=to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=g+THnNIhXb4I1Hax0SNl1UEHbEI4ZOIHd6uYzFFXr4o=; b=Cn7Efh9SkvYhhpBqQViaYu2xpqNo4vxOopPJFY8R9X2k4VXuZHGXIOzZWWlOL9LW3Z pqgUE0uzejmEhDgZDutr2qtFkz2E4wwvpXoMldZSjGh5VAAxXnxiTAL6tF63hPFF6bKJ dV4R05auJ1FllX42bMymQ0ouT2MK0xfI65ycBQZmNcKstzfLKA5AZ87CBncA25Ng8SPl 3rdO1eo1z1MqF3K+YRzam8ulAWu0nF1LWej4NbwfbziBk2nMHV2Sn4thqo61hAczxbYM UtHCgHEx4OowA95OQVE81oHpwj0lDKgoqSZcA8EbtRPvfAVXj8MOHUBQ/p0Q0ZUoUY/B AYHg== X-Forwarded-Encrypted: i=1; AJvYcCVYhtTnTa4B62V50uq2TpNwxnKveSsDaL5A+5hl1nPmEG95LmAmwyVRlxv083cUEDJK1IrRFpWQYnv1xbbvadTY@vger.kernel.org X-Gm-Message-State: AOJu0Ywf4ceC7tBC0k74ZvqsGiVN+4mV+Tmc7GWylayBH7fNsjsO2p6L ZoqaRroz96UOlUJUsiSY8QpmSqmiodSYYXJ1vUHKkXmhl26iVAE4ncAtOXel9T/wcuDu5kSsiDZ MueH/m7XCOw== X-Received: from dlbvs12.prod.google.com ([2002:a05:7022:3f0c:b0:12a:6d14:dfd9]) (user=irogers job=prod-delivery.src-stubby-dispatcher) by 2002:a05:7022:4582:b0:12a:6c84:6039 with SMTP id a92af1059eb24-12a726dd70amr2048952c88.41.1774061107157; Fri, 20 Mar 2026 19:45:07 -0700 (PDT) Date: Fri, 20 Mar 2026 19:44:45 -0700 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.53.0.959.g497ff81fa9-goog Message-ID: <20260321024446.692008-1-irogers@google.com> Subject: [PATCH v1 1/2] libbpf: Fix strict aliasing violations in hashmap From: Ian Rogers To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Alexander Shishkin , Ian Rogers , Adrian Hunter , James Clark , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Content-Type: text/plain; charset="UTF-8" The hashmap implementation contained strict aliasing violations. Specifically, the hashmap_cast_ptr(p) macro was casting pointers (such as void **) to long *, and these were subsequently dereferenced in functions like hashmap_insert(), hashmap_find(), and hashmap_delete(). C's strict aliasing rules (C11 6.5/7) prohibit accessing an object through an lvalue of an incompatible type. Dereferencing a long * to write to a void * object is a violation, even if they share the same size, as they are not compatible types. This can lead to undefined behavior, especially with aggressive compiler optimizations. Fix this by: 1. Updating hashmap_insert(), hashmap_find(), and hashmap_delete() to take void * for their output parameters (old_key, old_value, and value). 2. Modifying the implementation to use memcpy() and memset() for accessing these output parameters. Accessing an object as an array of characters (as done by memcpy) is a permitted exception to the strict aliasing rules. 3. Updating the hashmap_cast_ptr(p) macro to return void *, ensuring compatibility with the new function signatures while preserving the static assertion that ensures the pointed-to type matches the size of a long. Input parameters (key and value) remain as long, as they involve value conversion rather than incompatible pointer dereferencing, which is safe under strict aliasing rules. Signed-off-by: Ian Rogers --- tools/lib/bpf/hashmap.c | 21 +++++++++++---------- tools/lib/bpf/hashmap.h | 8 ++++---- 2 files changed, 15 insertions(+), 14 deletions(-) diff --git a/tools/lib/bpf/hashmap.c b/tools/lib/bpf/hashmap.c index 140ee4055676..ef50d262a126 100644 --- a/tools/lib/bpf/hashmap.c +++ b/tools/lib/bpf/hashmap.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include #include "hashmap.h" @@ -153,24 +154,24 @@ static bool hashmap_find_entry(const struct hashmap *map, int hashmap_insert(struct hashmap *map, long key, long value, enum hashmap_insert_strategy strategy, - long *old_key, long *old_value) + void *old_key, void *old_value) { struct hashmap_entry *entry; size_t h; int err; if (old_key) - *old_key = 0; + memset(old_key, 0, sizeof(long)); if (old_value) - *old_value = 0; + memset(old_value, 0, sizeof(long)); h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits); if (strategy != HASHMAP_APPEND && hashmap_find_entry(map, key, h, NULL, &entry)) { if (old_key) - *old_key = entry->key; + memcpy(old_key, &entry->key, sizeof(long)); if (old_value) - *old_value = entry->value; + memcpy(old_value, &entry->value, sizeof(long)); if (strategy == HASHMAP_SET || strategy == HASHMAP_UPDATE) { entry->key = key; @@ -203,7 +204,7 @@ int hashmap_insert(struct hashmap *map, long key, long value, return 0; } -bool hashmap_find(const struct hashmap *map, long key, long *value) +bool hashmap_find(const struct hashmap *map, long key, void *value) { struct hashmap_entry *entry; size_t h; @@ -213,12 +214,12 @@ bool hashmap_find(const struct hashmap *map, long key, long *value) return false; if (value) - *value = entry->value; + memcpy(value, &entry->value, sizeof(long)); return true; } bool hashmap_delete(struct hashmap *map, long key, - long *old_key, long *old_value) + void *old_key, void *old_value) { struct hashmap_entry **pprev, *entry; size_t h; @@ -228,9 +229,9 @@ bool hashmap_delete(struct hashmap *map, long key, return false; if (old_key) - *old_key = entry->key; + memcpy(old_key, &entry->key, sizeof(long)); if (old_value) - *old_value = entry->value; + memcpy(old_value, &entry->value, sizeof(long)); hashmap_del_entry(pprev, entry); free(entry); diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h index 0c4f155e8eb7..a888bf8c05de 100644 --- a/tools/lib/bpf/hashmap.h +++ b/tools/lib/bpf/hashmap.h @@ -116,7 +116,7 @@ enum hashmap_insert_strategy { _Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) || \ sizeof(*(p)) == sizeof(long), \ #p " pointee should be a long-sized integer or a pointer"); \ - (long *)(p); \ + (void *)(p); \ }) /* @@ -128,7 +128,7 @@ enum hashmap_insert_strategy { */ int hashmap_insert(struct hashmap *map, long key, long value, enum hashmap_insert_strategy strategy, - long *old_key, long *old_value); + void *old_key, void *old_value); #define hashmap__insert(map, key, value, strategy, old_key, old_value) \ hashmap_insert((map), (long)(key), (long)(value), (strategy), \ @@ -147,14 +147,14 @@ int hashmap_insert(struct hashmap *map, long key, long value, #define hashmap__append(map, key, value) \ hashmap__insert((map), (key), (value), HASHMAP_APPEND, NULL, NULL) -bool hashmap_delete(struct hashmap *map, long key, long *old_key, long *old_value); +bool hashmap_delete(struct hashmap *map, long key, void *old_key, void *old_value); #define hashmap__delete(map, key, old_key, old_value) \ hashmap_delete((map), (long)(key), \ hashmap_cast_ptr(old_key), \ hashmap_cast_ptr(old_value)) -bool hashmap_find(const struct hashmap *map, long key, long *value); +bool hashmap_find(const struct hashmap *map, long key, void *value); #define hashmap__find(map, key, value) \ hashmap_find((map), (long)(key), hashmap_cast_ptr(value)) -- 2.53.0.959.g497ff81fa9-goog