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smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="DZuoZrQy"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="qRpVT1Ez" From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1750520542; 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=s4i8scJlAGV+GpOYEKKV1KzgbXWXKbnRcAtdwbZvm+o=; b=DZuoZrQywZo0EWOkvlZ6JKShxNfBI3anJJsSF2LlOA6eey7KS5Ix8wFcpkZuxC/uwWdblX fSmnXB0Is9HURc/t2PsZSw8X0uNseZamH3EPrKEsxRQWEK4LNKFMBcRibffpZjRwb+3UFE 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3/3] vdso: Reject absolute relocations during build In-Reply-To: <20250612155635-ecade4e1-0235-464a-bcb3-293f7452510a@linutronix.de> References: <20250611-vdso-absolute-reloc-v3-0-47897d73784b@linutronix.de> <20250611-vdso-absolute-reloc-v3-3-47897d73784b@linutronix.de> <7ddda233-99f7-468b-842d-8469f0a86e77@ghiti.fr> <20250612155635-ecade4e1-0235-464a-bcb3-293f7452510a@linutronix.de> Date: Sat, 21 Jun 2025 17:42:20 +0200 Message-ID: <87cyaxp0df.ffs@tglx> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Thu, Jun 12 2025 at 16:21, Thomas Wei=C3=9Fschuh wrote: > On Thu, Jun 12, 2025 at 10:31:20AM +0200, Alexandre Ghiti wrote: > We could introduce per-architecture configuration. Essentially reverting = parts > of commit aff69273af61 ("vdso: Improve cmd_vdso_check to check all dynami= c relocations"). > The final logic for the intermediary objects still needs to be more compl= icated > than for the final .so as those contain relocations in the debug informat= ion. > > Or we could add a C hostprog for validation. > That would be much more flexible than the inline shell command. > It would then also be easier to use an allow-list than the brittle deny-l= ist. > > Or we don't do anything, relying on the selftests to detect miscompilatio= ns. That's a bad idea :) > I'll run this by tglx. If somebody else has any opinions, I'm all ears. This is all a mess because the relocation type numbers and their R_* names are not uniform accross architectures. Neither are the valid relocation types which are suitable for VDSO. I don't think you can reasonably cover all of it with readelf and grep. I did some unrelated relocation analysis some time ago and I just modified the python script (yes, I hate to use libelf) to show case how insane this gets. This is just as much as I needed to analyse files compiled with some random cross gcc I had handy. But you surely get the idea. Thanks, tglx --- #!/usr/bin/env python3 import sys from argparse import ArgumentParser from elftools.elf.elffile import ELFFile from elftools.elf.relocation import RelocationSection from elftools.elf.enums import ENUM_RELOC_TYPE_i386, ENUM_RELOC_TYPE_x64 from elftools.elf.enums import ENUM_RELOC_TYPE_ARM, ENUM_RELOC_TYPE_AARCH64 from elftools.elf.descriptions import describe_reloc_type class relocs(object): def __init__(self, arch, sections, types): self.arch =3D arch self.sections =3D sections self.types =3D types i386_relocs =3D relocs('EM_386', [ '.rel.text' ], [ ENUM_RELOC_TYPE_i386['R_386_NONE'], ENUM_RELOC_TYPE_i386['R_386_PC32'], ENUM_RELOC_TYPE_i386['R_386_GOTPC'], ENUM_RELOC_TYPE_i386['R_386_GOTOFF'], ]) x86_64_relocs =3D relocs('EM_X86_64', [ '.rela.text' ], [ ENUM_RELOC_TYPE_x64['R_X86_64_NONE'], ENUM_RELOC_TYPE_x64['R_X86_64_PC32'], ]) arm_relocs =3D relocs('EM_ARM', [ '.rela.text' ], # Probably incomplete [ ENUM_RELOC_TYPE_ARM['R_ARM_NONE'], ENUM_RELOC_TYPE_ARM['R_ARM_REL32'], ]) arm64_relocs =3D relocs('EM_AARCH64', [ '.rela.text' ], # Probably incomplete [ ENUM_RELOC_TYPE_AARCH64['R_AARCH64_NONE'], ENUM_RELOC_TYPE_AARCH64['R_AARCH64_ADR_PREL_LO21'], ]) # Minimal set for an example VDSO build ENUM_RELOC_TYPE_RISCV =3D dict( R_RISCV_BRANCH =3D 0x10, R_RISCV_PCREL_HI20 =3D 0x17, R_RISCV_PCREL_LO12_I =3D 0x18, R_RISCV_RVC_BRANCH =3D 0x2c, R_RISCV_RVC_JUMP =3D 0x2d, R_RISCV_RELAX =3D 0x33, ) riscv_relocs =3D relocs('EM_RISCV', [ '.rela.text' ], [ ENUM_RELOC_TYPE_RISCV['R_RISCV_BRANCH'], ENUM_RELOC_TYPE_RISCV['R_RISCV_PCREL_HI20'], ENUM_RELOC_TYPE_RISCV['R_RISCV_PCREL_LO12_I'], ENUM_RELOC_TYPE_RISCV['R_RISCV_RVC_BRANCH'], ENUM_RELOC_TYPE_RISCV['R_RISCV_RVC_JUMP'], ENUM_RELOC_TYPE_RISCV['R_RISCV_RELAX'], ]) supported_archs =3D { 'i386' : i386_relocs, 'x86_64' : x86_64_relocs, 'arm' : arm_relocs, 'arm64' : arm64_relocs, 'riscv' : riscv_relocs, } # Probably incomplete invalid_relocs =3D [ '.rela.dyn', '.rela.plt' ] def check_relocations(file, arch): elf =3D ELFFile(file) res =3D 0 if elf.header['e_machine'] !=3D arch.arch: print(elf.header['e_machine'], arch.arch) raise Exception('Architecture mismatch') for section in elf.iter_sections(): if not isinstance(section, RelocationSection): continue if section.name in invalid_relocs: print('Invalid VDSO relocation section: %s' %section.name) res +=3D 1 continue if section.name not in arch.sections: continue for reloc in section.iter_relocations(): if reloc['r_info_type'] in arch.types: continue res +=3D 1 symt =3D elf.get_section(section['sh_link']) sym =3D symt.get_symbol(reloc['r_info_sym']) type =3D describe_reloc_type(reloc['r_info_type'], elf) print("Invalid VDSO relocation: %s %s" %(type, sym.name)) return res if __name__ =3D=3D '__main__': parser =3D ArgumentParser(usage =3D 'usage: %(prog)s arch elf-file', description =3D 'magic VDSO section checker', prog =3D 'vdsoreloc') parser.add_argument('arch', choices =3D supported_archs.keys(), help =3D 'Target architecture') parser.add_argument('file', help =3D 'ELF file to parse') args =3D parser.parse_args() with open(args.file, 'rb') as file: try: res =3D check_relocations(file, supported_archs[args.arch]) sys.exit(res) except Exception as ex: # Do something sensible here print(ex) sys.exit(1)