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

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Message-Id: <20250821-nios2-implement-clone3-v1-1-1bb24017376a@siemens-energy.com>
Date: Thu, 21 Aug 2025 13:27:37 +0200
From: Simon Schuster via B4 Relay <devnull+schuster.simon.siemens-energy.com@...nel.org>
To: Dinh Nguyen <dinguyen@...nel.org>, 
 Christian Brauner <brauner@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
 Andrew Morton <akpm@...ux-foundation.org>, 
 David Hildenbrand <david@...hat.com>, 
 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, 
 Simon Schuster <schuster.simon@...mens-energy.com>
Subject: [PATCH 1/2] copy_process: Handle architectures where
 sizeof(unsigned long) < sizeof(u64)

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.

Signed-off-by: Simon Schuster <schuster.simon@...mens-energy.com>
---
 kernel/fork.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 5115be549234..0e9b2dd6c365 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1510,7 +1510,7 @@ static struct mm_struct *dup_mm(struct task_struct *tsk,
 	return NULL;
 }

-static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
+static int copy_mm(u64 clone_flags, struct task_struct *tsk)
 {
 	struct mm_struct *mm, *oldmm;

@@ -1548,7 +1548,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 	return 0;
 }

-static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
+static int copy_fs(u64 clone_flags, struct task_struct *tsk)
 {
 	struct fs_struct *fs = current->fs;
 	if (clone_flags & CLONE_FS) {
@@ -1569,7 +1569,7 @@ static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 	return 0;
 }

-static int copy_files(unsigned long clone_flags, struct task_struct *tsk,
+static int copy_files(u64 clone_flags, struct task_struct *tsk,
 		      int no_files)
 {
 	struct files_struct *oldf, *newf;
@@ -1599,7 +1599,7 @@ static int copy_files(unsigned long clone_flags, struct task_struct *tsk,
 	return 0;
 }

-static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
+static int copy_sighand(u64 clone_flags, struct task_struct *tsk)
 {
 	struct sighand_struct *sig;

@@ -1648,7 +1648,7 @@ static void posix_cpu_timers_init_group(struct signal_struct *sig)
 	posix_cputimers_group_init(pct, cpu_limit);
 }

-static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
+static int copy_signal(u64 clone_flags, struct task_struct *tsk)
 {
 	struct signal_struct *sig;

-- 
2.39.5