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Message-ID: <202401251509.17795F434@keescook> Date: Thu, 25 Jan 2024 15:10:24 -0800 From: Kees Cook <keescook@...omium.org> To: Nathan Chancellor <nathan@...nel.org> Cc: akpm@...ux-foundation.org, masahiroy@...nel.org, nicolas@...sle.eu, linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev, patches@...ts.linux.dev, linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, linux@...linux.org.uk, ardb@...nel.org, linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com, will@...nel.org, mark.rutland@....com, mpe@...erman.id.au, npiggin@...il.com, aneesh.kumar@...nel.org, naveen.n.rao@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org, paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, conor@...nel.org, linux-riscv@...ts.infradead.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH 00/11] Bump the minimum supported version of LLVM to 13.0.1 On Thu, Jan 25, 2024 at 03:55:06PM -0700, Nathan Chancellor wrote: > Hi all, > > This series bumps the minimum supported version of LLVM for building the > kernel to 13.0.1. The first patch does the bump and all subsequent > patches clean up all the various workarounds and checks for earlier > versions. > > Quoting the first patch's commit message for those that were only on CC > for the clean ups: > > When __builtin_mul_overflow() has arguments that differ in terms of > signedness and width, LLVM may generate a libcall to __muloti4 because > it performs the checks in terms of 65-bit multiplication. This issue > becomes harder to hit (but still possible) after LLVM 12.0.0, which > includes a special case for matching widths but different signs. > > To gain access to this special case, which the kernel can take advantage > of when calls to __muloti4 appear, bump the minimum supported version of > LLVM for building the kernel to 13.0.1. 13.0.1 was chosen because there > is minimal impact to distribution support while allowing a few more > workarounds to be dropped in the kernel source than if 12.0.0 were > chosen. Looking at container images of up to date distribution versions: > > archlinux:latest clang version 16.0.6 > debian:oldoldstable-slim clang version 7.0.1-8+deb10u2 (tags/RELEASE_701/final) > debian:oldstable-slim Debian clang version 11.0.1-2 > debian:stable-slim Debian clang version 14.0.6 > debian:testing-slim Debian clang version 16.0.6 (19) > debian:unstable-slim Debian clang version 16.0.6 (19) > fedora:38 clang version 16.0.6 (Fedora 16.0.6-3.fc38) > fedora:latest clang version 17.0.6 (Fedora 17.0.6-1.fc39) > fedora:rawhide clang version 17.0.6 (Fedora 17.0.6-1.fc40) > opensuse/leap:latest clang version 15.0.7 > opensuse/tumbleweed:latest clang version 17.0.6 > ubuntu:focal clang version 10.0.0-4ubuntu1 > ubuntu:latest Ubuntu clang version 14.0.0-1ubuntu1.1 > ubuntu:rolling Ubuntu clang version 16.0.6 (15) > ubuntu:devel Ubuntu clang version 17.0.6 (3) > > The only distribution that gets left behind is Debian Bullseye, as the > default version is 11.0.1; other distributions either have a newer > version than 13.0.1 or one older than the current minimum of 11.0.0. > Debian has easy access to more recent LLVM versions through > apt.llvm.org, so this is not as much of a concern. There are also the > kernel.org LLVM toolchains, which should work with distributions with > glibc 2.28 and newer. > > Another benefit of slimming up the number of supported versions of LLVM > for building the kernel is reducing the build capacity needed to support > a matrix that builds with each supported version, which allows a matrix > to reallocate the freed up build capacity towards something else, such > as more configuration combinations. > > This passes my build matrix with all supported versions. > > This is based on Andrew's mm-nonmm-unstable to avoid trivial conflicts > with my series to update the LLVM links across the repository [1] but I > can easily rebase it to linux-kbuild if Masahiro would rather these > patches go through there (and defer the conflict resolution to the merge > window). > > [1]: https://lore.kernel.org/20240109-update-llvm-links-v1-0-eb09b59db071@kernel.org/ > > --- > Nathan Chancellor (11): > kbuild: Raise the minimum supported version of LLVM to 13.0.1 > Makefile: Drop warn-stack-size plugin opt > x86: Drop stack-alignment plugin opt > ARM: Remove Thumb2 __builtin_thread_pointer workaround for Clang > arm64: Kconfig: Clean up tautological LLVM version checks > powerpc: Kconfig: Remove tautology in CONFIG_COMPAT > riscv: Remove MCOUNT_NAME workaround > riscv: Kconfig: Remove version dependency from CONFIG_CLANG_SUPPORTS_DYNAMIC_FTRACE > fortify: Drop Clang version check for 12.0.1 or newer > lib/Kconfig.debug: Update Clang version check in CONFIG_KCOV > compiler-clang.h: Update __diag_clang() macros for minimum version bump > > Documentation/process/changes.rst | 2 +- > Makefile | 8 -------- > arch/arm/include/asm/current.h | 8 +------- > arch/arm64/Kconfig | 5 +---- > arch/powerpc/Kconfig | 1 - > arch/riscv/Kconfig | 2 -- > arch/riscv/include/asm/ftrace.h | 14 ++------------ > arch/riscv/kernel/mcount.S | 10 +++++----- > arch/x86/Makefile | 6 ------ > include/linux/compiler-clang.h | 8 ++------ > lib/Kconfig.debug | 2 +- > scripts/min-tool-version.sh | 2 +- > scripts/recordmcount.pl | 2 +- > security/Kconfig | 2 -- > 14 files changed, 15 insertions(+), 57 deletions(-) > --- > base-commit: 979741ebd48f75ed6d101c7290e3325340d361ff > change-id: 20240124-bump-min-llvm-ver-to-13-0-1-39f84dd36b19 > > Best regards, > -- > Nathan Chancellor <nathan@...nel.org> > Yes, please. :) This looks reasonable -- I appreciate the review of default Clang versions across distros! Reviewed-by: Kees Cook <keescook@...omium.org> -- Kees Cook
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