From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (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 8006620B7FB for ; Wed, 4 Jun 2025 20:43:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749069811; cv=none; b=dw6pbzH2iMyF+iO3hoipDx+nDISImldnzRxaGIVWpbqoHlQgRiP83/OXQAhz/8aNdqtbPmKFhAhDrwTy3ZUolIe5m/Mg5kc0BYkPa2JNHUcs/4hHBIMavwJuLIUv19dEyV0UPnhlG58dH6qcBUhdFdiJpqv2N7m7gVaid7jTfbw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749069811; c=relaxed/simple; bh=VtQomjkQ1v7EOUbApbJYxBp1+UgpB5K8Xt5XxZW82jI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LWntOjbJxgU1dM23BpdCY+8m/c6o/2TKp1trvXqt2q8b84uJWeLQFKjrpZOjWGDnrClWp92ffjdP2qDcUkso9tdFVej9JXzf9SQ8SmCYbKjhQvCBinPQGsrEvSKFGetYRIdp3DRx9fy9j8lMWwhaQlv3DzYBz7AVaw+0d8+LtVI= 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=vFTKHTdY; arc=none smtp.client-ip=95.215.58.173 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="vFTKHTdY" Message-ID: <292afb4a-78ce-4f42-a322-d2fb5c0da241@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1749069806; 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=Vb5JSS9eL4fyESaxlTwcgXF7p3wGHCpWrs+V8cj86OQ=; b=vFTKHTdYVcLEWp6EROOfPtYeh97ajcMWTb+FwmGtBt/rJhW9tcDuyflm23uWWOSZqBmldt mKHNNkMPf/kvurLmOKk9e9wVP/f+BHckotGCVupYhSGwGqjX1R+aXZfvgC2FE/Vo+0pweV 2SFSht1erEIHxMuIXD7+SyZ5a8DUG5Q= Date: Wed, 4 Jun 2025 13:42:53 -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 Content-Language: en-GB To: Ihor Solodrai , 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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. 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") > >