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. Cc: stable@vger.kernel.org # all applicable Closes: https://github.com/ClangBuiltLinux/linux/issues/2174 Signed-off-by: Nathan Chancellor --- This is based on mm-unstable due to the move of arch_numa.c from mm/ to drivers/base/ living there. I have CC'd stable because this warning appears in my testing back to at least 6.1 but I see no reason why it should not apply to all trees. No fixes tag since this is a layered problem that just happens to appear under certain conditions. Another alternative would be using the __assume macro to say something like __assume(nr_node_ids <= MAX_NUMNODES); but that seems a little more fragile than an outright check. --- Changes in v2: - Add missing newline to print message (Andrew + sashiko) - Print MAX_NUMNODES using '%u' specifier to match nr_node_ids - Link to v1: https://patch.msgid.link/20260811-arch_numa-avoid-fortify-warning-v1-1-59ce3e689f3a@kernel.org --- mm/arch_numa.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/mm/arch_numa.c b/mm/arch_numa.c index 442ea239bba7..459fa60a5621 100644 --- a/mm/arch_numa.c +++ b/mm/arch_numa.c @@ -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]); --- base-commit: 47870fb9b0e3bd20b45e3a069b4c766f3dcb721a change-id: 20260811-arch_numa-avoid-fortify-warning-66af87403412 Best regards, -- Cheers, Nathan