From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 0F8B02236FD; Mon, 21 Jul 2025 20:14:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753128877; cv=none; b=Mh7JYSGj5moFlYfhbbQ7sOuRnHCjI7KPknehWuxAHgs7B/2S8z9AxtUB9onhaIXMNedlNEELb5+Vs3XRhRbwDUKKgEKOsMioBR8w+KZwfQbNIOJdfuwzct8SV5+ovIYtMD+MIEi5Wn86JDkdjwZmr1yGTwd5Q4GDLY5NYlRbeyI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753128877; c=relaxed/simple; bh=4r/4nG1qgmsh/c5VG19N2iiUSmLvYYkyHl3DeygcpXA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MhzxgDWdlJ0HMexi0D6afif5SDahzMtkLQHqf/P+Xiru62VdSsf0D9ns7YVvreL/O41l1YtyfSyN2IVxh64o4bfHo2dSkc/z3NuaXfNxsf0raOCus6V0AzdSJ08dTpiuo3xwPDwvgoGlnLe2UcEEpOKrkzHOOWS6pm2vbHig4nM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lFAdcpLW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lFAdcpLW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78896C4CEF4; Mon, 21 Jul 2025 20:14:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753128876; bh=4r/4nG1qgmsh/c5VG19N2iiUSmLvYYkyHl3DeygcpXA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lFAdcpLWaHxUml6OxVBwU6HF1hrXLHYFkb/H/aJEA6dwrS3fNYgpHHD9vBXhtoV4B DnlKcNVrSuy3OpcCNz5sLZixJ87BNNsHf8Wz/iXbKKuKn/4kGIyWtHqBOtZbDd1IXJ HugdwrRmbPiDKguHMjzYQAyiU+QjuAhDHP4sI+9soOwfvMemYiSYDeWbZvGVJV9Fex I+fr6vfi5W5pHpIw/Uwwc0t82cvI6vzhJdTGqyaczDCk68iZYr7Dm3hhNM2Cwu5lkJ 0NpKGkTxKOKNy3D+Lz3rZTszczYJyLaRnmSD0gVfod3q27zUYqquJUIShZDNnZldk2 WRNb0JXBCq60A== Date: Mon, 21 Jul 2025 13:14:36 -0700 From: Kees Cook To: Will Deacon Cc: Ard Biesheuvel , Mike Rapoport , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paolo Bonzini , Vitaly Kuznetsov , Henrique de Moraes Holschuh , Hans de Goede , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , "Rafael J. Wysocki" , Len Brown , Masami Hiramatsu , Michal Wilczynski , Juergen Gross , Andy Shevchenko , "Kirill A. Shutemov" , Roger Pau Monne , David Woodhouse , Usama Arif , "Guilherme G. Piccoli" , Thomas Huth , Brian Gerst , kvm@vger.kernel.org, ibm-acpi-devel@lists.sourceforge.net, platform-driver-x86@vger.kernel.org, linux-acpi@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , "Gustavo A. R. Silva" , Christoph Hellwig , Andrey Konovalov , Andrey Ryabinin , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH v3 04/13] x86: Handle KCOV __init vs inline mismatches Message-ID: <202507211311.8DAC4C7@keescook> References: <20250717231756.make.423-kees@kernel.org> <20250717232519.2984886-4-kees@kernel.org> <202507181541.B8CFAC7E@keescook> Precedence: bulk X-Mailing-List: sparclinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jul 21, 2025 at 01:47:55PM +0100, Will Deacon wrote: > On Sun, Jul 20, 2025 at 04:10:01PM +1000, Ard Biesheuvel wrote: > > On Sat, 19 Jul 2025 at 08:51, Kees Cook wrote: > > > On Fri, Jul 18, 2025 at 11:36:32AM +0300, Mike Rapoport wrote: > > > > On Thu, Jul 17, 2025 at 04:25:09PM -0700, Kees Cook wrote: > > > > > When KCOV is enabled all functions get instrumented, unless the > > > > > __no_sanitize_coverage attribute is used. To prepare for > > > > > __no_sanitize_coverage being applied to __init functions, we have to > > > > > handle differences in how GCC's inline optimizations get resolved. For > > > > > x86 this means forcing several functions to be inline with > > > > > __always_inline. > > > > > > > > > > Signed-off-by: Kees Cook > > > > > > > > ... > > > > > > > > > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > > > > > index bb19a2534224..b96746376e17 100644 > > > > > --- a/include/linux/memblock.h > > > > > +++ b/include/linux/memblock.h > > > > > @@ -463,7 +463,7 @@ static inline void *memblock_alloc_raw(phys_addr_t size, > > > > > NUMA_NO_NODE); > > > > > } > > > > > > > > > > -static inline void *memblock_alloc_from(phys_addr_t size, > > > > > +static __always_inline void *memblock_alloc_from(phys_addr_t size, > > > > > phys_addr_t align, > > > > > phys_addr_t min_addr) > > > > > > > > I'm curious why from all memblock_alloc* wrappers this is the only one that > > > > needs to be __always_inline? > > > > > > Thread-merge[1], adding Will Deacon, who was kind of asking the same > > > question. > > > > > > Based on what I can tell, GCC has kind of fragile inlining logic, in the > > > sense that it can change whether or not it inlines something based on > > > optimizations. It looks like the kcov instrumentation being added (or in > > > this case, removed) from a function changes the optimization results, > > > and some functions marked "inline" are _not_ inlined. In that case, we end up > > > with __init code calling a function not marked __init, and we get the > > > build warnings I'm trying to eliminate. > > Got it, thanks for the explanation! > > > > So, to Will's comment, yes, the problem is somewhat fragile (though > > > using either __always_inline or __init will deterministically solve it). > > > We've tripped over this before with GCC and the solution has usually > > > been to just use __always_inline and move on. > > > > > > > Given that 'inline' is already a macro in the kernel, could we just > > add __attribute__((__always_inline__)) to it when KCOV is enabled? > > That sounds like a more robust approach and, by the sounds of it, we > could predicate it on GCC too. That would also provide a neat place for > a comment describing the problem. > > Kees, would that work for you? That seems like an extremely large hammer for this problem, IMO. It feels like it could cause new strange corner cases. I'd much prefer the small fixes I've currently got since it keeps it focused. KCOV is already enabled for "allmodconfig", so any new instances would be found very quickly, etc. (And GCC's fragility in this regard has already been exposed to these cases -- it's just that I changed one of the combinations of __init vs inline vs instrumentation. I could give it a try, if you really prefer the big hammer approach... -- Kees Cook