linux-kernel - Re: [PATCH 6.1.y] KVM: arm64: silence -Wuninitialized-const-pointer warning

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250725163851.GB684490@ax162>
Date: Fri, 25 Jul 2025 09:38:51 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Justin Stitt <justinstitt@...gle.com>, Marc Zyngier <maz@...nel.org>,
	James Morse <james.morse@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Tom Rix <trix@...hat.com>,
	Christopher Covington <cov@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH 6.1.y] KVM: arm64: silence -Wuninitialized-const-pointer
 warning

On Fri, Jul 25, 2025 at 10:58:05AM +0200, Greg KH wrote:
> On Thu, Jul 24, 2025 at 06:15:28PM -0700, Justin Stitt wrote:
> > A new warning in Clang 22 [1] complains that @clidr passed to
> > get_clidr_el1() is an uninitialized const pointer. get_clidr_el1()
> > doesn't really care since it casts away the const-ness anyways.
> 
> Is clang-22 somehow now a supported kernel for the 6.1.y tree?  Last I
> looked, Linus's tree doesn't even build properly for it, so why worry
> about this one just yet?

Our goal is to have tip of tree LLVM / clang be able to build any
supported branch of the kernel so that whenever it branches and
releases, the fixes for it are already present in released kernel
versions so users can just pick them up and go. We are going to have to
worry about this at some point since it is a stable-only issue so why
not tackle it now?

> > Silence the warning by initializing the struct.
> 
> Why not fix the compiler not to do this instead?  We hate doing foolish
> work-arounds for broken compilers.

While casting away the const from the pointer in this case is "fine"
because the object it pointed to was not const, I am fairly certain it
is undefined behavior to cast away the const from a pointer to a const
object, see commit 12051b318bc3 ("mips: avoid explicit UB in assignment
of mips_io_port_base") for an exampile, so I am not sure the warning is
entirely unreasonable.

Cheers,
Nathan