FAILED: patch "[PATCH] arch_numa: avoid false positive fortify warning in" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x f2b1cb39d5ccab090d8353788f186f7e7a1fffd4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090313-footwork-agonizing-e163@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f2b1cb39d5ccab090d8353788f186f7e7a1fffd4 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <[email protected]>
Date: Thu, 13 Aug 2026 20:12:55 -0700
Subject: [PATCH] arch_numa: avoid false positive fortify warning in
setup_node_to_cpumask_map()

When building ARCH=riscv using clang with CONFIG_FORTIFY_SOURCE and CONFIG_UBSAN_BOUNDS enabled, CONFIG_NR_CPUS > 64, and the default value of 2 for CONFIG_NODES_SHIFT, there is a compiletime warning from the fortify routines.

In file included from mm/arch_numa.c:11:
In file included from include/linux/acpi.h:14:
In file included from include/linux/resource_ext.h:11:
In file included from include/linux/slab.h:17:
In file included from include/linux/gfp.h:7:
In file included from include/linux/mmzone.h:8:
In file included from include/linux/spinlock.h:60:
In file included from include/linux/interrupt_rc.h:17:
In file included from include/linux/smp.h:13:
In file included from include/linux/cpumask.h:11:
In file included from include/linux/bitmap.h:13:
In file included from include/linux/string.h:383:
include/linux/fortify-string.h:430:4: warning: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribue-warning]

    430 |                         __write_overflow_field(p_size_field, size);
        |                         ^
  include/linux/fortify-string.h:430:4: note: called by function 'fortify_memset_chk(unsigned long, unsigned long, unsigned long)'
  include/linux/bitmap.h:248:3: note: inlined by function 'setup_node_to_cpumask_map'
    248 |                 memset(dst, 0, len);
        |                 ^
  include/linux/fortify-string.h:462:25: note: expanded from macro 'memset'
    462 | #define memset(p, c, s) __fortify_memset_chk(p, c, s,                   \
        |                         ^
  include/linux/fortify-string.h:453:2: note: expanded from macro '__fortify_memset_chk'
    453 |         fortify_memset_chk(__fortify_size, p_size, p_size_field),       \
        |         ^
  include/linux/fortify-string.h:430:4: note: use '-gline-directives-only' (implied by '-g1') or higher for more accurate inlining chain locations
    430 |                         __write_overflow_field(p_size_field, size);
        |                         ^

1 warning generated.

In this configuration, MAX_NUMNODES is 4. clang unrolls the for loop in setup_node_to_cpumask_map() past this, which triggers the fortify check when accessing node_to_cpumask_map on the theoretical fifth loop iteration because it would be an out of bounds write.

Make it clear to clang that nr_node_ids is bounded by MAX_NUMNODES due to the logic in setup_nr_node_ids() by early returning in setup_node_to_cpumask_map() should that condition be violated.

index 442ea239bba7..459fa60a5621 100644
@@ -105,6 +105,18 @@ static void __init setup_node_to_cpumask_map(void)
 	if (nr_node_ids == MAX_NUMNODES)
 		setup_nr_node_ids();
 
+	/*
+	 * This check should never be true but it makes it clear to compilers
+	 * that node_to_cpumask_map is bound by nr_node_ids, avoiding false
+	 * positive fortify warnings when accessing node_to_cpumask_map in the
+	 * for loop below.
+	 */
+	if (unlikely(nr_node_ids > MAX_NUMNODES)) {
+		pr_err("nr_node_ids (%u) is larger than MAX_NUMNODES (%u)\n",
+		       nr_node_ids, MAX_NUMNODES);
+		return;
+	}
+
 	/* allocate and clear the mapping */
 	for (node = 0; node < nr_node_ids; node++) {
 		alloc_bootmem_cpumask_var(&node_to_cpumask_map[node]);