From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (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 C93D021421C for ; Wed, 4 Jun 2025 20:58:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749070714; cv=none; b=IIvvTWQfQvmyLPuBSn2Ps3Q77+VLyZbScpOmHLRvDHtbQyXyaG75Ss2JOLSFSC/+n/Oy8y1DrdG5dLJG5VXGLchMkukz1ZzL0ZzC7TAggzmGJff64PJy6MqyJfY3TleykYif69WMy7ClSL7K3H5CRB3taPERdwEeOJ8J2pgpGGI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749070714; c=relaxed/simple; bh=yl43/TjLt9UGhLhdDVk7aoKantS+Y2srC4b9YG8ZeZM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k48o7sEUEqSthf7+DWOwPd51634oPmlN3/1NsKWhRmpeOx1IYCn5QpgasA9UzKV/EyE60YEFdlVNp6/NPsZ5myMZRNkoRZnfRcOIe+0figJg9iyhnO7xavEZmjkIr2KYaObIXVgyikOkSzvDZ6oOr50A4BSQ+3iNJPUGriWp/bQ= 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=ZNs9ucc6; arc=none smtp.client-ip=91.218.175.184 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="ZNs9ucc6" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1749070709; 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=zjy048oBaCIaLwZeN29bwuVzNbcXKjQrK1pbSHCDd/g=; b=ZNs9ucc6h06FSQy5JDHAdwSb6b3N7HIlvUhvenGnoKas+NmFKlX3oqQYs8lD3k9Dapu+XA 3M3vIel48UmRk6QFGMztLvuoWo1/RDf2/UePQxsycVQaoNiYyylmxpHgZHysMR6BnuE7bA RityOnlDe2+8myiIgX04gGUv7mSHbm0= Date: Wed, 4 Jun 2025 13:58:21 -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 2/3] selftests/bpf: add cmp_map_pointer_with_const test To: Yonghong Song , andrii@kernel.org Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, mykolal@fb.com, kernel-team@meta.com References: <20250604003759.1020745-1-isolodrai@meta.com> <20250604003759.1020745-2-isolodrai@meta.com> <292afb4a-78ce-4f42-a322-d2fb5c0da241@linux.dev> 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: <292afb4a-78ce-4f42-a322-d2fb5c0da241@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/4/25 1:42 PM, Yonghong Song wrote: > > > On 6/4/25 9:44 AM, Ihor Solodrai wrote: >> On 6/3/25 5:37 PM, Ihor Solodrai wrote: >>> Add a test for CONST_PTR_TO_MAP comparison with a non-0 constant. A >>> BPF program with this code must not pass verification in unpriv. >>> >>> Signed-off-by: Ihor Solodrai >>> --- >>>   .../selftests/bpf/progs/verifier_unpriv.c       | 17 +++++++++++++++++ >>>   1 file changed, 17 insertions(+) >>> >>> diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/ >>> tools/testing/selftests/bpf/progs/verifier_unpriv.c >>> index 28200f068ce5..85b41f927272 100644 >>> --- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c >>> +++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c >>> @@ -634,6 +634,23 @@ l0_%=:    r0 = 0;                        \ >>>       : __clobber_all); >>>   } >>>   +SEC("socket") >>> +__description("unpriv: cmp map pointer with const") >>> +__success __failure_unpriv __msg_unpriv("R1 pointer comparison >>> prohibited") >>> +__retval(0) >>> +__naked void cmp_map_pointer_with_const(void) >>> +{ >>> +    asm volatile ("                    \ >>> +    r1 = 0;                        \ >>> +    r1 = %[map_hash_8b] ll;                \ >>> +    if r1 == 0xcafefeeddeadbeef goto l0_%=;        \ >> >> GCC BPF caught (correctly) that this is not a valid instruction >> because imm is supposed to be 32bit [1]: >> >>     progs/verifier_unpriv.c: Assembler messages: >>     progs/verifier_unpriv.c:643: Error: immediate out of range, shall >> fit in 32 bits >>     make: *** [Makefile:751: /tmp/work/bpf/bpf/src/tools/testing/ >> selftests/bpf/bpf_gcc/verifier_unpriv.bpf.o] Error 1 >> >> But LLVM 20 let it compile and the test passes. I wonder whether it's >> a bug in LLVM worth reporting? >> >> [1] https://github.com/kernel-patches/bpf/actions/runs/15430930573/ >> job/43428666342 > > This is a missed case for llvm. See: >   https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/BPF/ > MCTargetDesc/BPFMCCodeEmitter.cpp#L82-L85 > Basically for the following code, > > unsigned BPFMCCodeEmitter::getMachineOpValue(const MCInst &MI, >                                              const MCOperand &MO, >                                              SmallVectorImpl > &Fixups, >                                              const MCSubtargetInfo > &STI) const { >   if (MO.isReg()) >     return MRI.getEncodingValue(MO.getReg()); >   if (MO.isImm()) >     return static_cast(MO.getImm()); > > For 'static_cast(MO.getImm())', MO.getImm() value is a s64, so > casting to u32 should check > the value range and we didn't check them, hence didn't report an error. I see. Out of curiosity I looked at llvm-objdump and indeed only lower 32 bits are in the binary: 0000000000000320 : 100: b7 01 00 00 00 00 00 00 r1 = 0x0 101: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0x0 ll 103: 15 01 00 00 ef be ad de if r1 == -0x21524111 goto +0x0 Thanks for checking, Yonghong. > > The following is the fix: >    if (MO.isReg()) >      return MRI.getEncodingValue(MO.getReg()); > -  if (MO.isImm()) > +  if (MO.isImm()) { > +    assert(MO.getImm() >= INT_MIN && MO.getImm() <= INT_MAX); >      return static_cast(MO.getImm()); > +  } > > With the above, if the clang build enables assertion, the following dump > will show up: > > clang: /home/yhs/work/llvm-project/llvm/lib/Target/BPF/MCTargetDesc/ > BPFMCCodeEmitter.cpp:86: unsigned int (anonymous > namespace)::BPFMCCodeEmitter::getMachin > eOpValue(const MCInst &, const MCOperand &, SmallVectorImpl &, > const MCSubtargetInfo &) const: Assertion `MO.getImm() >= INT_MIN && > MO.getImm() <= > INT_MAX' failed. > > Although llvm tends to use 'assert' a lot (and 'assert' thing will > become noop on production > build), e.g., > > [~/work/llvm-project/llvm/lib/Target/BPF/MCTargetDesc (release/19.x)]$ > grep assert *.cpp > BPFAsmBackend.cpp:#include > BPFAsmBackend.cpp:  assert(unsigned(Kind - FirstTargetFixupKind) < > getNumFixupKinds() && > BPFAsmBackend.cpp:    assert(Value <= UINT32_MAX); > BPFAsmBackend.cpp:    assert(Fixup.getKind() == FK_PCRel_2); > BPFELFObjectWriter.cpp:        assert(SectionELF && "Null section for > reloc symbol"); > BPFInstPrinter.cpp:  assert(Kind == MCSymbolRefExpr::VK_None); > BPFInstPrinter.cpp:  assert((Modifier == nullptr || Modifier[0] == 0) && > "No modifiers supported"); > BPFInstPrinter.cpp:    assert(Op.isExpr() && "Expected an expression"); > BPFInstPrinter.cpp:  assert(RegOp.isReg() && "Register operand not a > register"); > BPFInstPrinter.cpp:    assert(0 && "Expected an immediate"); > BPFMCCodeEmitter.cpp:#include > BPFMCCodeEmitter.cpp:  assert(MO.isExpr()); > BPFMCCodeEmitter.cpp:  assert(Expr->getKind() == MCExpr::SymbolRef); > BPFMCCodeEmitter.cpp:  assert(Op1.isReg() && "First operand is not > register."); > BPFMCCodeEmitter.cpp:  assert(Op2.isImm() && "Second operand is not > immediate."); > > Production build tends not to enable assertion for performance reason, so > I guess we could emit an error to user for such cases. Will fix in llvm21. > >> >>> +l0_%=:    r0 = 0; \ >>> +    exit;                        \ >>> +"    : >>> +    : __imm_addr(map_hash_8b) >>> +    : __clobber_all); >>> +} >>> + >>>   SEC("socket") >>>   __description("unpriv: write into frame pointer") >>>   __failure __msg("frame pointer is read only") >> >> >