From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f49.google.com (mail-wm1-f49.google.com [209.85.128.49]) (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 3833E2D1911 for ; Mon, 22 Jun 2026 23:01:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.49 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782169288; cv=none; b=n3wUlLdYMtWUjYeMVJSXoDt8wr2ykXaBmXeg8aLFau+k7oIrSrLfABv6OUoZ1LhHDzNsJ5c+Sl3qu9vWvz/0qB+G7mn3f9y2FMGJX3OYphoP1FIM9KZgk40X7B90GJexhPEe16wk3TG9gnT5Kt5iUkJ0IcuSjDMRd/R/V0q9ajs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782169288; c=relaxed/simple; bh=M6hXi84S5gmVIUuWj+KozD+bYt5YW3hsLAnkoVvRJf0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=l6C4T/Enic9TnuCVzIOhe11FSgQX9uXez91fvskn2eSoYht1o3kwBQw0obPWtIu3fOKlmPYnoSnBUx4dIWYPqTjV3KffedK+ovnJcYW0623Phpi6Cr6J8xsV9pTROiwb51iEdq9V/Zup62YTU/DzNZx243RMwr/nEpgw38EqKIk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=siuOBNh8; arc=none smtp.client-ip=209.85.128.49 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="siuOBNh8" Received: by mail-wm1-f49.google.com with SMTP id 5b1f17b1804b1-4923fb1f095so37230105e9.1 for ; Mon, 22 Jun 2026 16:01:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782169286; x=1782774086; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=gl7x5/Ly0sc1rwSAjd0rqRNSTSQbeRuLQa2LMGScITQ=; b=siuOBNh8g0yWlcpVkpkGAcldwx1oAYYM2L8BeAQCS8RkgvQY/jDfo23ANv3MV2Jy+6 Ucv2Vs/EcZqAENPWHGSUpM57CTNR1tAvq48HgF6W6v8EbEU6e15LNm0e+UBhrqEu4PrX 2piNXHSN6wmpEa6lBwarP67fMzKUM8SBHk4bFc5aE5PcqQEWfxNfZiVaVH6l+tKXpW1/ YcVslVgWIh7ttehfaGFAWL2GpzU+L+v1wJz8hVzvEDN0oWieSBPgpZdxCH7evn7k/K3+ oZOVXLpmLQDaRm1z5cl8PQi+4U2YG1DNKjnoe05fjFid9pFzn7ve3Dy3qtSs8EP/C6kY dhRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782169286; x=1782774086; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=gl7x5/Ly0sc1rwSAjd0rqRNSTSQbeRuLQa2LMGScITQ=; b=lKrcL6+zdKhDw5G4jh3SW75RwzLQgkU0tup9KzaH19PQtq/HJEvu//8Yz7yHjoAqN8 kSqomNi5yugCSBvu8vwfyLkdGo2Mgi+muu6dlsEjkPGSG83QYJ4M8rkAbuIcNZpO77i6 hG8vVtYcbsi5/s1//KCqj/Sb6a1NVM0h/ip5LEeatTjIYR4DG5xMbFOtOTrkZuyg687O Ff2RiZNCkTjPeLCZBq52SOCDzkX/dBv9mt67bl+c8lakLdcUVgZrTZdT8msg+s5e2yqW PwAUf34jZAsuYVKdoZeTnq2idyOu1D+ciRhskk2M2iaxopgPVPBAskbpHJIO0NohrTKq 5sPg== X-Forwarded-Encrypted: i=1; AFNElJ8cgjJHXLs5AUs/zYxlhk9reS3FWNNzSrrIFO2g+5CZXbX9w7/02bR8KE/jJeCsTrEPLxdaM58=@vger.kernel.org X-Gm-Message-State: AOJu0YzLzUFjhIoP9kIvGtOnjq+AWC8YRG0N2TH7zR8VbMQmAldFaEJg PZtM24vP9vXy007Nr5EDkiD7QxAhCq+RGNhMYAyhS04qCm0TpkYhFHM= X-Gm-Gg: AfdE7clxfiRPOQSpQjRHDw4UuBm1FMPpsiY/gBJdMEei/d6ZGFkgX4+hVPuwDIqwc5m QZtoAmIqDd9hVDP+xmV2yB9p32zwrPf6EpT9DViV++PkVxXdPvN5GR+/K5A7XKnOQvhm5/GtWQ0 xMc//TuX66LVSWx5ZpUqJMqqrxgppmgKZ9QA09Nb3q861ZFoVuXjFdFvhMsCq2o3Q9T8CVg0I1k Zhf9VrDC98pzA8yLIwQabAN2XZPxBozuewmAE1+kA/vXmnJ32QMH38mL9OEnJo5BEyQw2pE+tgl Eoxfo6Mt02SZOYBEefF0mdKVkMqDc9rWtT/7z7d2vhTGnR7MYPuF4LZmqESqvGMWuWc9X9sBejq PaJ+67RKN0KFLFTuiWWHvhNxL/T4BoB5Zr23oPA6qhQ2uVVwAnc49ht2uOw== X-Received: by 2002:a05:600c:8b77:b0:492:4911:8a with SMTP id 5b1f17b1804b1-4925b35a0f9mr2465495e9.12.1782169285687; Mon, 22 Jun 2026 16:01:25 -0700 (PDT) Received: from debian.. ([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4923fd1fa34sm371339255e9.5.2026.06.22.16.01.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jun 2026 16:01:24 -0700 (PDT) From: Tristan Madani To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: Eduard Zingerman , Xu Kuohai , Jiri Olsa , John Fastabend , Martin KaFai Lau , bpf@vger.kernel.org, stable@vger.kernel.org, tristan@talencesecurity.com Subject: [PATCH bpf v3 1/2] bpf: Reset register bounds before narrowing retval range in check_mem_access() Date: Mon, 22 Jun 2026 23:01:22 +0000 Message-ID: <20260622230123.3695446-2-tristmd@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260622230123.3695446-1-tristmd@gmail.com> References: <20260622230123.3695446-1-tristmd@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani When the BPF verifier processes a context load of an LSM hook return value, it calls __mark_reg_s32_range() to narrow the register to the hook's valid range. However, __mark_reg_s32_range() intersects the new range with the register's existing bounds using max_t()/min_t() rather than replacing them. If the destination register carries stale bounds from a prior instruction (e.g. BPF_MOV64_IMM), the intersection can produce a range narrower than reality. The verifier then believes it knows the register's exact value, while at runtime the actual hook return value is loaded, creating a verifier/runtime mismatch that can be used to bypass BPF memory safety checks. The else branch already calls mark_reg_unknown() to reset register state before any narrowing. Apply the same reset in the is_retval path so stale bounds are cleared before __mark_reg_s32_range() intersects. Fixes: 5d99e198be27 ("bpf, lsm: Add check for BPF LSM return value") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a2b348f98080..21a365d436a5 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6201,6 +6201,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, struct b */ if (info.reg_type == SCALAR_VALUE) { if (info.is_retval && get_func_retval_range(env->prog, &range)) { + mark_reg_unknown(env, regs, value_regno); err = __mark_reg_s32_range(env, regs, value_regno, range.minval, range.maxval); if (err) -- 2.47.3