From nobody Fri Feb 13 09:48:11 2026 Received: from mail-wr1-f73.google.com (mail-wr1-f73.google.com [209.85.221.73]) (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 5896C2E636 for ; Mon, 15 Apr 2024 07:58:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713167930; cv=none; b=leBggl535teucRQUh+BnhSmse5IXhHt0qggiW43xnLxPWKue44iemdH/CJ5LFeHmhi4XIG0KMJhbj89p3BZtPuMtqb6k2zQcLRTEjtxPTbeKbEHlRfqsG19//fhy5SJxk0Kl5MpdTwaKA0yp9sra66vHvqPtJBiUgUVCzSYp7JQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713167930; c=relaxed/simple; bh=J2hRLplVLxqxMA6E8xzPuTVt84azbEdp5qYIhiP3Ytk=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=jW4X8pzm1rvLn4/voHzjbFMd0lYSPibOqNIhrkAD2Q5DlLFDPjDy3sEDa5j/6u93+nUdQzwDvLQ3WZfAD1wCITGwuALrtLC3aPq7lRM5VFkGppAIT1fnw4Ei+fiyb/hRD2PlNLl78/j1vk5Z5P94spApVIrKa1nELS9bkTB8U14= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--ardb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=4o/R5ay3; arc=none smtp.client-ip=209.85.221.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--ardb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="4o/R5ay3" Received: by mail-wr1-f73.google.com with SMTP id ffacd0b85a97d-347f92ab882so109538f8f.0 for ; Mon, 15 Apr 2024 00:58:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1713167926; x=1713772726; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=olXUbwFvWhAHV+rAKgvFMgGXe2ohRAJCIFGXNNajNx8=; b=4o/R5ay39sb9LNbrjYvQuZIw3KGQanF0UaQQ0TwM9FTmkyJQwEILAduA5WiEoh7F14 etT8hQX7ye9CIpurM/ex3KML7e6EhVLamI6GHF5lfSEdD4xDXKJ6cR1q6s+u/reYNXTs pJ+pIfrTPp4SPNtY4G/WKiArnxFAO/BjLSaVtNUj0zzWA1V/Scpb+Ze1dwHuwtvJx94y QrtdLbbO4Hc8MipCf65diB//q+P2PUHXQ7CBI0z6AJwczJpw4mXGDHK29/Y2Itxi8nXD RCCEwJ+JlMEzpLahWFSH8TsfZZgH/V8kumQNyY2KW/lZzU6/JtWrsDa/t/f5POhHvv3a lxnA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713167926; x=1713772726; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=olXUbwFvWhAHV+rAKgvFMgGXe2ohRAJCIFGXNNajNx8=; b=uhTep+VZ98/cT12hq0AVtMsDgIEaoG8r3hKiWQrKheTJdSEOBOJCY0pUtwcc8Bh6g0 c0s+Kcl+s/2v1MkLjD2X/pI8fhARmH1TC9BBqNs4DVx09o3BAErxc0Ynkd6vLaCM/K/p SJxoLCZt2Y1/1EOYfoLigAnHf6kGiXZRJGUZRzj8sMbweuE9bWDk9DA7qLWBwpmr6m+8 mUL6X4m5rbu0gWZRNC0rMU7fnD6K9KU1vbiCIaCdQMLlQ4M8OO/7sUZSmRrSnOhLcATb jn2B2znjj/1xUsVI2Pqz5ENWXpDChtzPGOT+21JiwEvF4vNxMYhQt4X5nUX6X7bGA0kK 2FcA== X-Gm-Message-State: AOJu0Yz5IQcqtLszHYeJRjE5WE3MtGn/CPGAY5ukdBSvMrxmjoxOOJpW 7XPWss6xrBzgBZ1GynRDBdCQ+1zZAVN8C+XK+RWProJxjQw9ux23urWg07EgwV3w000Tk05FUKO xGm+gfPdbJKkFZAQ/nO8f3P9ioS9TWoaXGC+cxXSWR4p5ZYlEBNqO/gz9VH0uHYNvEjXaDHEBnE LO6MOjgquFRIY4skvVSQaGaiIpHBAOjw== X-Google-Smtp-Source: AGHT+IFwDxTcJaKceCQkM1kYIKiVHmoTc2lMM/DBuKq1nDl6RA24l/dE3t+Vmaqnmzc+9t8IXzRS1sNi X-Received: from palermo.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:118a]) (user=ardb job=sendgmr) by 2002:a5d:6043:0:b0:33d:5804:7f6e with SMTP id j3-20020a5d6043000000b0033d58047f6emr18071wrt.4.1713167926026; Mon, 15 Apr 2024 00:58:46 -0700 (PDT) Date: Mon, 15 Apr 2024 09:58:39 +0200 In-Reply-To: <20240415075837.2349766-5-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240415075837.2349766-5-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=5390; i=ardb@kernel.org; h=from:subject; bh=V4aOk/fz1+fDF2STMCLU+VVQ7hXwmmgXF9wA63lernQ=; b=owGbwMvMwCFmkMcZplerG8N4Wi2JIU3mnn7VugcM9mKl8d6vVHKWyArYhkd23LGffr56kkK50 KrJ01Z0lLIwiHEwyIopsgjM/vtu5+mJUrXOs2Rh5rAygQxh4OIUgIkcE2BkOBbydmeS7RWFDW// CitHCJ+MNrAteHPxKqece02DZq+9F8NfyRdpwiwpizTy9DS8a2d6uio1u+x22l+3rsCRiWO9zWl WAA== X-Mailer: git-send-email 2.44.0.683.g7961c838ac-goog Message-ID: <20240415075837.2349766-6-ardb+git@google.com> Subject: [PATCH v3 1/3] kallsyms: Avoid weak references for kallsyms symbols From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: Ard Biesheuvel , Masahiro Yamada , Arnd Bergmann , Martin KaFai Lau , linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org, bpf@vger.kernel.org, Andrii Nakryiko , Jiri Olsa , Nick Desaulniers , Kees Cook Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel kallsyms is a directory of all the symbols in the vmlinux binary, and so creating it is somewhat of a chicken-and-egg problem, as its non-zero size affects the layout of the binary, and therefore the values of the symbols. For this reason, the kernel is linked more than once, and the first pass does not include any kallsyms data at all. For the linker to accept this, the symbol declarations describing the kallsyms metadata are emitted as having weak linkage, so they can remain unsatisfied. During the subsequent passes, the weak references are satisfied by the kallsyms metadata that was constructed based on information gathered from the preceding passes. Weak references lead to somewhat worse codegen, because taking their address may need to produce NULL (if the reference was unsatisfied), and this is not usually supported by RIP or PC relative symbol references. Given that these references are ultimately always satisfied in the final link, let's drop the weak annotation, and instead, provide fallback definitions in the linker script that are only emitted if an unsatisfied reference exists. While at it, drop the FRV specific annotation that these symbols reside in .rodata - FRV is long gone. Tested-by: Nick Desaulniers # Boot Reviewed-by: Nick Desaulniers Reviewed-by: Kees Cook Acked-by: Arnd Bergmann Link: https://lkml.kernel.org/r/20230504174320.3930345-1-ardb%40kernel.org Signed-off-by: Ard Biesheuvel --- include/asm-generic/vmlinux.lds.h | 19 +++++++++++++ kernel/kallsyms.c | 6 ---- kernel/kallsyms_internal.h | 30 ++++++++------------ 3 files changed, 31 insertions(+), 24 deletions(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinu= x.lds.h index f7749d0f2562..e8449be62058 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -448,11 +448,30 @@ #endif #endif =20 +/* + * Some symbol definitions will not exist yet during the first pass of the + * link, but are guaranteed to exist in the final link. Provide preliminary + * definitions that will be superseded in the final link to avoid having to + * rely on weak external linkage, which requires a GOT when used in positi= on + * independent code. + */ +#define PRELIMINARY_SYMBOL_DEFINITIONS \ + PROVIDE(kallsyms_addresses =3D .); \ + PROVIDE(kallsyms_offsets =3D .); \ + PROVIDE(kallsyms_names =3D .); \ + PROVIDE(kallsyms_num_syms =3D .); \ + PROVIDE(kallsyms_relative_base =3D .); \ + PROVIDE(kallsyms_token_table =3D .); \ + PROVIDE(kallsyms_token_index =3D .); \ + PROVIDE(kallsyms_markers =3D .); \ + PROVIDE(kallsyms_seqs_of_names =3D .); + /* * Read only Data */ #define RO_DATA(align) \ . =3D ALIGN((align)); \ + PRELIMINARY_SYMBOL_DEFINITIONS \ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ __start_rodata =3D .; \ *(.rodata) *(.rodata.*) \ diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 18edd57b5fe8..22ea19a36e6e 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -325,12 +325,6 @@ static unsigned long get_symbol_pos(unsigned long addr, unsigned long symbol_start =3D 0, symbol_end =3D 0; unsigned long i, low, high, mid; =20 - /* This kernel should never had been booted. */ - if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE)) - BUG_ON(!kallsyms_addresses); - else - BUG_ON(!kallsyms_offsets); - /* Do a binary search on the sorted kallsyms_addresses array. */ low =3D 0; high =3D kallsyms_num_syms; diff --git a/kernel/kallsyms_internal.h b/kernel/kallsyms_internal.h index 27fabdcc40f5..85480274fc8f 100644 --- a/kernel/kallsyms_internal.h +++ b/kernel/kallsyms_internal.h @@ -5,27 +5,21 @@ #include =20 /* - * These will be re-linked against their real values - * during the second link stage. + * These will be re-linked against their real values during the second link + * stage. Preliminary values must be provided in the linker script using t= he + * PROVIDE() directive so that the first link stage can complete successfu= lly. */ -extern const unsigned long kallsyms_addresses[] __weak; -extern const int kallsyms_offsets[] __weak; -extern const u8 kallsyms_names[] __weak; +extern const unsigned long kallsyms_addresses[]; +extern const int kallsyms_offsets[]; +extern const u8 kallsyms_names[]; =20 -/* - * Tell the compiler that the count isn't in the small data section if the= arch - * has one (eg: FRV). - */ -extern const unsigned int kallsyms_num_syms -__section(".rodata") __attribute__((weak)); - -extern const unsigned long kallsyms_relative_base -__section(".rodata") __attribute__((weak)); +extern const unsigned int kallsyms_num_syms; +extern const unsigned long kallsyms_relative_base; =20 -extern const char kallsyms_token_table[] __weak; -extern const u16 kallsyms_token_index[] __weak; +extern const char kallsyms_token_table[]; +extern const u16 kallsyms_token_index[]; =20 -extern const unsigned int kallsyms_markers[] __weak; -extern const u8 kallsyms_seqs_of_names[] __weak; +extern const unsigned int kallsyms_markers[]; +extern const u8 kallsyms_seqs_of_names[]; =20 #endif // LINUX_KALLSYMS_INTERNAL_H_ --=20 2.44.0.683.g7961c838ac-goog