From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ot1-f45.google.com (mail-ot1-f45.google.com [209.85.210.45]) (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 1F4FE31353C for ; Wed, 15 Jul 2026 06:40:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784097654; cv=none; b=NczMeUv8VXi/ncrDCdTHUKocudkUFbgd7wmcAPLaxfyMHsRUNKakkmdxp3rhh5QA/iyPGfRcRfMltgn8Tjhz4mykvU6u9eB+QASa6kZURAl1eSZ/GSbNoexRfc576AAHrntn+CKG6QfNJvZuuusX4jnJpbcKRV4BJXJK0EUjPoQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784097654; c=relaxed/simple; bh=knjNBY6KXAPQZlQe9bRNtDcGvCjmUroOBBgMdrKU/6g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QMmIZrfFk1iFtqvbJnEGfhevfypAfMleCIUkIyR/nLcn48Rb9X7CtZOzJF24nj3/+wx8jBYA/x6Dlftat0jcs8q8qCb9MBOkEHp2seJhw3y0kHU+zFz5y0mAZwyJpg150VOVYdAbGnnh5fqimdylfqv1ld4CA3B9t/tnF24drnw= 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=LsOhXMFV; arc=none smtp.client-ip=209.85.210.45 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="LsOhXMFV" Received: by mail-ot1-f45.google.com with SMTP id 46e09a7af769-7eb1dc6bd53so2740229a34.2 for ; Tue, 14 Jul 2026 23:40:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1784097652; x=1784702452; 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:content-type; bh=RnUjOU2zNsXgWD5I54XqK3e2II0iMbHQ5Y9pLOU3ZO8=; b=LsOhXMFVdcj0q6HIEOH4Xxgo54353y8h1e9Y3cSlXn09sHsuMke1bdwVdE4gxJlSFt 0kPsoyQ3d5PjRttPOl+Gvhf/udB0A6cdKzoKsIBLW7VOJlVqfhWOQj0ejGcSTIpc6G84 HH6YY3twBfQDtomoBZHYzRIkdu02ADlpdOnkgswpmA+33gNvRukneNE6fqT4DK7ytdkY 2HXs98ZWsXBdcj8QnHC48jwz7Dz1aydK4lc2We+QHOcF8wFFixAdSWQORcpK0VsgL01+ BNKdA0DC2Ej7hOf6sRoKu0S0VcJenANzAAs5KS8VFzwB2lLqFtKVWAYpbor8WBuXQxvD UYiQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784097652; x=1784702452; 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:content-type; bh=RnUjOU2zNsXgWD5I54XqK3e2II0iMbHQ5Y9pLOU3ZO8=; b=ENQrp6GJ47KaqdShy0ZCJxvpAHrMTe9lE/CKicvAL7Lu9cfgCzt4XUoNyJBb6T4VYZ moR7iLa2Jsw/M1dYfQbJ8yGg8SiEXEDTNiWwDobJ3NvVyIUzg6d2S/hKwdsabsluTuv2 n4aAmIqUpkxfWy95DIQvNV1eqEm4PtTnbfjH9si4XnJ+M1I7t/5fzVEwoWL+gUmwOCPn cOyReZyZfgtlshFF3lVsXFvXW+J79qiiL74RTIcj0sK8mEXaVuhfhid1gv5CXRnx3ZIf 6Y7eVILDBTHMCiyVpNBWVlCw5+HgpVdA+asxdhY/1x3q231BzD9Mt/0ntduFbltBIFnu K8tw== X-Gm-Message-State: AOJu0YwbPUzrZMJ7iCQgn1N6UBXfMGJ1WWXsAmYMTHB3sLwWKRQdm6XC xWEgnPQuKxsi24FnCVZzIymwg9rPhJ/D011rGlSaNLT284jC+IWB5x4t6Ieisw== X-Gm-Gg: AfdE7ckerKWvqi0CEMVJFmEq5rJRJAqIX+akYHZW/3psYsu9f/JPPbk5/ptzrJUDKxV fjdOiwCMpt0Nu1U7244wr9nwSkAPH9uDopoBEh7/EeHmWXSdmlHj73TCfmBq7RbqN/IMj+bsHa6 ubDnGMEms1Qed/vnNwZtFV3sqtegeP/bt0gUYb7nHQMmJ9x+8bLUFOXLhbGgePeqQUNdy5gl5D8 5tpdQta/j3AAeoZ0y9vnbpnpjXGtpJ91ENK2bdGYFB+uEdoHJ3b53ZIvAmEO2FlKFV51SHxRL9Q c6HEgpugd8uYgoOEbBZbJgpR5e3vXBKfwdAZHUvOPoyyz+UMblyR6+F/UBt4sq5VS27s6Y8nFQg qfPHcvaKt1Q7YVYLW0H7ifwjvsl8bWGhOakgD3e8euEbYM5PBEaER/QPMYK1zo+gTKOnGiI9mJP 6i5Y5rpkqNFwZW X-Received: by 2002:a05:6830:6519:b0:7eb:6891:c372 with SMTP id 46e09a7af769-7ec4a946e1emr3086906a34.13.1784097651794; Tue, 14 Jul 2026 23:40:51 -0700 (PDT) Received: from localhost ([2a03:2880:ff:8::]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7ebcae206e2sm16665730a34.2.2026.07.14.23.40.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2026 23:40:51 -0700 (PDT) From: Amery Hung To: bpf@vger.kernel.org Cc: alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, memxor@gmail.com, ameryhung@gmail.com, kernel-team@meta.com Subject: [PATCH bpf-next v2 1/7] bpf: Remove dynptr check in check_stack_range_initialized() Date: Tue, 14 Jul 2026 23:40:41 -0700 Message-ID: <20260715064047.1793790-2-ameryhung@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260715064047.1793790-1-ameryhung@gmail.com> References: <20260715064047.1793790-1-ameryhung@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit For a MEM_UNINIT ("raw mode") helper argument, check_stack_range_initialized() open-coded a scan that rejected any STACK_DYNPTR slot in the range with "potential write to dynptr". This duplicated, and was stricter than, the handling that runs when the buffer is actually marked initialized. check_helper_call() later replays the write byte by byte via check_mem_access(), which goes through destroy_if_dynptr_stack_slot(), which rejects overwritting a referenced dynptr. Therefore drop the redundant scan and rely on check_mem_access(). Acked-by: Eduard Zingerman Signed-off-by: Amery Hung --- kernel/bpf/verifier.c | 25 ------------------- .../testing/selftests/bpf/progs/dynptr_fail.c | 4 +-- 2 files changed, 2 insertions(+), 27 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 03e2202cca13..7dd961ede88d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6733,31 +6733,6 @@ static int check_stack_range_initialized( } if (meta && meta->raw_mode) { - /* Ensure we won't be overwriting dynptrs when simulating byte - * by byte access in check_helper_call using meta.access_size. - * This would be a problem if we have a helper in the future - * which takes: - * - * helper(uninit_mem, len, dynptr) - * - * Now, uninint_mem may overlap with dynptr pointer. Hence, it - * may end up writing to dynptr itself when touching memory from - * arg 1. This can be relaxed on a case by case basis for known - * safe cases, but reject due to the possibilitiy of aliasing by - * default. - */ - for (i = min_off; i < max_off + access_size; i++) { - int stack_off = -i - 1; - - spi = bpf_get_spi(i); - /* raw_mode may write past allocated_stack */ - if (state->allocated_stack <= stack_off) - continue; - if (state->stack[spi].slot_type[stack_off % BPF_REG_SIZE] == STACK_DYNPTR) { - verbose(env, "potential write to dynptr at off=%d disallowed\n", i); - return -EACCES; - } - } meta->access_size = access_size; meta->regno = reg_from_argno(argno); return 0; diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c index 344fb2aa0813..94489ac64da8 100644 --- a/tools/testing/selftests/bpf/progs/dynptr_fail.c +++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c @@ -1112,7 +1112,7 @@ int dynptr_overwrite_ref(void *ctx) /* Reject writes to dynptr slot from bpf_dynptr_read */ SEC("?raw_tp") -__failure __msg("potential write to dynptr at off=-16") +__failure __msg("cannot overwrite referenced dynptr") int dynptr_read_into_slot(void *ctx) { union { @@ -1558,7 +1558,7 @@ int BPF_PROG(skb_invalid_ctx_fexit, void *skb) /* Reject writes to dynptr slot for uninit arg */ SEC("?raw_tp") -__failure __msg("potential write to dynptr at off=-16") +__failure __msg("cannot overwrite referenced dynptr") int uninit_write_into_slot(void *ctx) { struct { -- 2.52.0