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 A6BD423B600; Mon, 21 Jul 2025 20:49:54 +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=1753130994; cv=none; b=XcF5tWe03lfzSPFwvh9DS8+1MX74O3iRvJOvF9EbsgSwioqcLgmaPwHtiunOnwHPf16v10FsTUXRoTD+1pCFNZu1G5gAOm4VPlddyagvA2gxIWOWN4II1j2v1s+JpKiHsiE3FnOPOHhSLJE/K4aV6DxWgLYdQkN3FSS6UMnB7Es= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753130994; c=relaxed/simple; bh=RGpMFousrm9JXr2aga1XoiQZq81gXpkDZQCrU7p8kG4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=J+n0C7+8nLAWgOnQW0vsAOF+FaLhTTplzKC54xFgeQ6Gu6Yfxn82pTzBXT7OIcicQDss77m0fR5TKg4i6AgdpM5k8LR3a1Qvi/HMsV6fjtQoClC2B2Nh+HMcxqviyz4ogdjjtSdxhmiUaMIn2yEw5re21gJzMp9WCXi7VWIa34g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=USwBlGGy; 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="USwBlGGy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4EA0DC4CEF7; Mon, 21 Jul 2025 20:49:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753130994; bh=RGpMFousrm9JXr2aga1XoiQZq81gXpkDZQCrU7p8kG4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=USwBlGGycUbYKwRlz8H1PUciShFkTuZXfVpLM5MtEpyQ2A97ZmBOIYa0cGOwBplAM P/UloDehuLPGSIqgqNRVeLye3ZQJwvjrIvND/8XbCEE/heb6TuWjlHXRTmnHic7i+/ ufyzJfA+Tj1dnxW4WNlS2ijwfnLETqFwratBaRXG4lRw2vboY071pv4Rgj4gG0uneL vJADYIT6M2Sug0BnFp+wdbmKStgy/2g++iMRLOa45PAedgg8EJByYxkT5u6rz9xzId 7//OhF3fMircm2SYJfkHca/mWkXbMTQEr5KB9GUZB1xfjt2aV3YLzdWsmNabD0jVLY gzg6qfQMQz07w== Date: Mon, 21 Jul 2025 13:49:53 -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: <202507211349.D93679FB25@keescook> References: <20250717231756.make.423-kees@kernel.org> <20250717232519.2984886-4-kees@kernel.org> <202507181541.B8CFAC7E@keescook> <202507211311.8DAC4C7@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: <202507211311.8DAC4C7@keescook> On Mon, Jul 21, 2025 at 01:14:36PM -0700, Kees Cook wrote: > 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... I gave it a try -- it fails spectacularly. ;) Let's stick to my small fixes instead? -- Kees Cook