linux-kernel - Re: [PATCH 1/2] copy_process: Handle architectures where sizeof(unsigned long)

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Message-ID: <8c6239a9-8414-469c-9b94-a43735b4e882@redhat.com>
Date: Thu, 21 Aug 2025 23:14:23 +0200
From: David Hildenbrand <david@...hat.com>
To: schuster.simon@...mens-energy.com, Dinh Nguyen <dinguyen@...nel.org>,
 Christian Brauner <brauner@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Kees Cook <kees@...nel.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] copy_process: Handle architectures where
 sizeof(unsigned long) < sizeof(u64)

On 21.08.25 13:27, Simon Schuster via B4 Relay wrote:
> From: Simon Schuster <schuster.simon@...mens-energy.com>
> 
> With the introduction of clone3 in commit 7f192e3cd316 ("fork: add
> clone3") the effective bit width of clone_flags on all architectures was
> increased from 32bit to 64bit. However, the signature of the copy_*
> helper functions (e.g., copy_sighand) used by copy_process was not
> adapted, as such, they potentially truncate the flags on architectures
> such as nios2, where unsigned long is a 32bit unsigned integer type.
> 
> This can, for instance, be observed via failures of kernel selftest
> clone3_clear_sighand, which attempts to trigger the conditional
> 
> 	if (clone_flags & CLONE_CLEAR_SIGHAND)
> 
> in function copy_sighand within fork.c that will always fail given:
> 
> 	unsigned long /* == uint32_t */ clone_flags
> 	#define CLONE_CLEAR_SIGHAND 0x100000000ULL
> 
> This commit fixes the bug by always passing clone_flags via their
> declared u64 type, invariant of architecture-dependent integer sizes.

Sounds reasonable.

But is this actually something that is already exposed before patch#2 on 
other architectures?

(I assume above output is with patch #2 but without patch #1)

If so, we need a Fixes:. If not, we're good.

-- 
Cheers

David / dhildenb