From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 428CC13C8FF for ; Thu, 26 Jun 2025 01:25:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750901160; cv=none; b=Hr3soG0Lhip76qeOKDAd2puzpmGD3jRz2GUipupS5UqqUNdaaMjZIe8h8EEqG+CEjZQTDR5UVE55EOGVqXEJQKJAvjvXIsErzAFbRvzgjBBJ3N5kyqRl27fuALVCBb0V6FHx1ALjneKAbIc/28+0l3o0gjohGrZlJpL2UOyyxBs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750901160; c=relaxed/simple; bh=Mma+smHy8Bn5YkWAgTrJRXkVdda5HC29vDWL+WVpnhM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UJ8o4DQr4N8Cxptuj0SQzUhETBM+VbuzP0hCvgdVbEXivezrJX2YcmuL+nnty2VHw5AGR5kK65yqKE4KApNdM+VTDfSMxPhKii1DW9dsjVij465vUooT2lTGckp/FpodgllEwbhHjH21engQd6Iej3dYpOPOEmyx17y2Ijq6QfQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=BBlUxsPK; arc=none smtp.client-ip=91.218.175.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="BBlUxsPK" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1750901155; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=z4OZ8zA7jIIESIfUjfoc872YxAKDYQLaX3efqeg+Rok=; b=BBlUxsPKzGqA/GDV+ghP+uB615XWNJYWVdhEckhE85e/uRZUzAOfFzJu8Q6i9fIynG9NqY 2NPrrUfI9/lLaJDlrGi76efvn9AsbnUNDwSBdsZYUQC5+mQZoIN9yQavTp0Ru0VakjOicl wiQrQp/HSo+Q0gWIbl3QTIB6euuvTJM= Date: Wed, 25 Jun 2025 18:25:49 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v2 2/2] selftests/bpf: add test cases for bpf_dynptr_memset() To: Mykyta Yatsenko , bpf@vger.kernel.org Cc: andrii@kernel.org, ast@kernel.org, eddyz87@gmail.com, mykolal@fb.com, kernel-team@meta.com References: <20250624205240.1311453-1-isolodrai@meta.com> <20250624205240.1311453-3-isolodrai@meta.com> <5f00c508-5150-4e69-b006-d15b0e6b2d23@gmail.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ihor Solodrai In-Reply-To: <5f00c508-5150-4e69-b006-d15b0e6b2d23@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/25/25 4:45 AM, Mykyta Yatsenko wrote: > On 6/24/25 21:52, Ihor Solodrai wrote: >> Add tests to verify the behavior of bpf_dynptr_memset(): >>    * normal memset 0 >>    * normal memset non-0 >>    * memset with an offset >>    * memset in dynptr that was adjusted >>    * error: size overflow >>    * error: offset+size overflow >>    * error: readonly dynptr >>    * memset into non-linear xdp dynptr >> >> Signed-off-by: Ihor Solodrai >> --- >>   .../testing/selftests/bpf/prog_tests/dynptr.c |   8 + >>   .../selftests/bpf/progs/dynptr_success.c      | 164 ++++++++++++++++++ >>   2 files changed, 172 insertions(+) >> >> diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c b/tools/ >> testing/selftests/bpf/prog_tests/dynptr.c >> index 62e7ec775f24..f2b65398afce 100644 >> --- a/tools/testing/selftests/bpf/prog_tests/dynptr.c >> +++ b/tools/testing/selftests/bpf/prog_tests/dynptr.c >> @@ -21,6 +21,14 @@ static struct { >> [...] >> + >> +SEC("xdp") >> +int test_dynptr_memset_xdp_chunks(struct xdp_md *xdp) >> +{ >> +    const int max_chunks = 200; >> +    struct bpf_dynptr ptr_xdp; >> +    u32 data_sz, offset = 0; A question not directly to Mykyta. So noalu32 version of this test was failing to verify with this: 118: (85) call bpf_dynptr_read#201 R2 min value is negative, either use unsigned or 'var &= const' Where R2 refers to `data_sz - offset` Full log here: https://github.com/kernel-patches/bpf/actions/runs/15861036149/job/44718289284 I tried various conditions unsuccessfully. But changing u32 to u64 made it work. If handle_tail part is removed, as Mykyta suggested, this doesn't matter, so I will probably leave u32 in v3. However I am curious if u32->u64 change is an appropriate workaround in general for noalu32 problems? AFAIU verifier might get confused by all the added shifts, and "noalu32" is a backward compatibility thing. >> +    char expected_buf[32]; > nit: expected_buf[32] = {DYNPTR_MEMSET_VAL}; I tried that at the beginning. As it turns out, this doesn't work in BPF the way you'd expect: Here is a piece of llvm-objdump with explicit memset: 0000000000000968 : 301: 18 02 00 00 2a 2a 2a 2a 00 00 00 00 2a 2a 2a 2a r2 = 0x2a2a2a2a2a2a2a2a ll 303: 7b 2a c8 ff 00 00 00 00 *(u64 *)(r10 - 0x38) = r2 304: 7b 2a d0 ff 00 00 00 00 *(u64 *)(r10 - 0x30) = r2 305: 7b 2a d8 ff 00 00 00 00 *(u64 *)(r10 - 0x28) = r2 306: 7b 2a e0 ff 00 00 00 00 *(u64 *)(r10 - 0x20) = r2 307: bf a7 00 00 00 00 00 00 r7 = r10 308: 07 07 00 00 e8 ff ff ff r7 += -0x18 309: b7 02 00 00 00 00 00 00 r2 = 0x0 310: bf 73 00 00 00 00 00 00 r3 = r7 311: 85 10 00 00 ff ff ff ff call -0x1 ... You can clearly see a piece of stack filling up with 0x2a After applying this diff: diff --git a/tools/testing/selftests/bpf/progs/dynptr_success.c b/tools/testing/selftests/bpf/progs/dynptr_success.c index 5120acb8b15a..5b351f6fe07c 100644 --- a/tools/testing/selftests/bpf/progs/dynptr_success.c +++ b/tools/testing/selftests/bpf/progs/dynptr_success.c @@ -809,12 +809,10 @@ int test_dynptr_memset_xdp_chunks(struct xdp_md *xdp) const int max_chunks = 200; struct bpf_dynptr ptr_xdp; u32 data_sz, chunk_sz, offset = 0; - char expected_buf[32]; + char expected_buf[32] = { DYNPTR_MEMSET_VAL }; char buf[32]; int i; - __builtin_memset(expected_buf, DYNPTR_MEMSET_VAL, sizeof(expected_buf)); - /* ptr_xdp is backed by non-contiguous memory */ bpf_dynptr_from_xdp(xdp, 0, &ptr_xdp); data_sz = bpf_dynptr_size(&ptr_xdp); We get the following: 0000000000000968 : 301: bf a7 00 00 00 00 00 00 r7 = r10 302: 07 07 00 00 e8 ff ff ff r7 += -0x18 303: b7 02 00 00 00 00 00 00 r2 = 0x0 304: bf 73 00 00 00 00 00 00 r3 = r7 305: 85 10 00 00 ff ff ff ff call -0x1 ... The stack allocated array is not initialized. Could be an LLVM bug/incompleteness? I used LLVM 19 while developing. >> +    char buf[32]; >> +    int i; >> + >> +    __builtin_memset(expected_buf, DYNPTR_MEMSET_VAL, >> sizeof(expected_buf)); >> + >> +    /* ptr_xdp is backed by non-contiguous memory */ >> +    bpf_dynptr_from_xdp(xdp, 0, &ptr_xdp); >> +    data_sz = bpf_dynptr_size(&ptr_xdp); >> + >> +    err = bpf_dynptr_memset(&ptr_xdp, 0, data_sz, DYNPTR_MEMSET_VAL); >> +    if (err) >> +        goto out; >> + > Maybe we can calculate max_chunks instead of hardcoding, something like: > max_chunks = data_sz / sizeof(expected_buf) + (data_sz % > sizeof(expected_buf) ? 1 : 0); I don't see a point of doing it for this test. max_chunks is just a big enough arbitrary constant that works. We do a similar thing in other tests. >> +    bpf_for(i, 0, max_chunks) { >> +        offset = i * sizeof(buf); >> +        err = bpf_dynptr_read(&buf, sizeof(buf), &ptr_xdp, offset, 0); > > handle_tail seems unnecessary, maybe handle tail in the main loop: > __u32 sz = min_t(data_sz - offset : sizeof(buf)); > bpf_dynptr_read(&buf, sz, &ptr_xdp, offset, 0); > Yeah, you're right. It ended up like this because I've been fighting the verifier while writing the test, and this version worked eventually. The critical piece to uncofuse it was changing: offset += sizeof(buf) to offset = i * sizeof(buf) I will have to add min_t macro locally though. >> +        switch (err) { >> +        case 0: >> +            break; >> +        case -E2BIG: >> +            goto handle_tail; >> +        default: >> +            goto out; >> +        } >> +        err = bpf_memcmp(buf, expected_buf, sizeof(buf)); >> +        if (err) >> +            goto out; >> +    } >> + >> +handle_tail: >> +    if (data_sz - offset < sizeof(buf)) { >> +        err = bpf_dynptr_read(&buf, data_sz - offset, &ptr_xdp, >> offset, 0); >> +        if (err) >> +            goto out; >> +        err = bpf_memcmp(buf, expected_buf, data_sz - offset); >> +    } >> +out: >> +    return XDP_DROP; >> +} >> + >>   void *user_ptr; >>   /* Contains the copy of the data pointed by user_ptr. >>    * Size 384 to make it not fit into a single kernel chunk when copying >