On Mon, Sep 14, 2026 at 11:59 PM Hao Ge <[email protected]> wrote:
>
> SHF_ALLOC means, per the ELF spec, that a section occupies memory
> during process execution. Some module sections occupy memory
> outside the regular module layout, for example the percpu section
> with its per-CPU allocations. The loader currently excludes such
> a section from the layout by clearing its SHF_ALLOC, which
> overloads the flag with a loader-internal meaning.
> apply_relocations() needs a special case for the section, and
> find_sec(".data..percpu") returns different results before and
> after layout_and_allocate().
>
> Introduce SH_ENTSIZE_STANDALONE to mark sections with a separate
> allocation. The percpu section is its first user. layout_sections()
> and move_module() skip marked sections, and apply_relocations() goes
> back to testing only SHF_ALLOC. Based on a patch by Petr Pavlu [1].
>
> .data..percpu keeps SHF_ALLOC, so it would now show up under
> /sys/module/*/sections/. The section has one instance per CPU and no
> single address to report, and the entry never existed before, so
> skip it in add_sect_attrs(). add_notes_attrs() indexes its attrs[]
> array and skips it too. No functional change otherwise.
And IIUC no userspace-visible changes too, right?
>
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Reported-by: Sashiko <[email protected]>
> Link:
> https://lore.kernel.org/all/[email protected]/ [1]
> Suggested-by: Petr Pavlu <[email protected]>
> Reviewed-by: Petr Pavlu <[email protected]>
> Cc: [email protected]
> Signed-off-by: Hao Ge <[email protected]>
Reviewed-by: Suren Baghdasaryan <[email protected]>
> ---
> include/linux/module.h | 2 ++
> kernel/module/internal.h | 8 ++++++++
> kernel/module/kallsyms.c | 13 +++----------
> kernel/module/main.c | 32 +++++++++++++++++---------------
> kernel/module/sysfs.c | 17 +++++++++++++----
> 5 files changed, 43 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 96cc98568eea..0c6f32ddcbf2 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -325,6 +325,8 @@ enum mod_mem_type {
> MOD_INIT_RODATA,
>
> MOD_MEM_NUM_TYPES,
> +
> + MOD_STANDALONE = -2,
> MOD_INVALID = -1,
> };
>
> diff --git a/kernel/module/internal.h b/kernel/module/internal.h
> index 061161cc79d9..4c738074a27b 100644
> --- a/kernel/module/internal.h
> +++ b/kernel/module/internal.h
> @@ -29,6 +29,14 @@
> #define SH_ENTSIZE_TYPE_MASK ((1UL << SH_ENTSIZE_TYPE_BITS) - 1)
> #define SH_ENTSIZE_OFFSET_MASK ((1UL << (BITS_PER_LONG -
> SH_ENTSIZE_TYPE_BITS)) - 1)
>
> +/*
> + * Marker for sections with a separate allocation, which are not placed
> + * into mod->mem[].
> + */
> +#define SH_ENTSIZE_STANDALONE \
> + (((unsigned long)MOD_STANDALONE & SH_ENTSIZE_TYPE_MASK) \
> + << SH_ENTSIZE_TYPE_SHIFT)
> +
> /* Maximum number of characters written by module_flags() */
> #define MODULE_FLAGS_BUF_SIZE (TAINT_FLAGS_COUNT + 4)
>
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index f23126d804b2..0dca6d40160e 100644
> --- a/kernel/module/kallsyms.c
> +++ b/kernel/module/kallsyms.c
> @@ -76,7 +76,7 @@ static char elf_type(const Elf_Sym *sym, const struct
> load_info *info)
> }
>
> static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
> - unsigned int shnum, unsigned int pcpundx)
> + unsigned int shnum)
> {
> const Elf_Shdr *sec;
> enum mod_mem_type type;
> @@ -86,11 +86,6 @@ static bool is_core_symbol(const Elf_Sym *src, const
> Elf_Shdr *sechdrs,
> !src->st_name)
> return false;
>
> -#ifdef CONFIG_KALLSYMS_ALL
> - if (src->st_shndx == pcpundx)
> - return true;
> -#endif
> -
> sec = sechdrs + src->st_shndx;
> type = sec->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT;
> if (!(sec->sh_flags & SHF_ALLOC)
> @@ -131,8 +126,7 @@ void layout_symtab(struct module *mod, struct load_info
> *info)
> /* Compute total space required for the core symbols' strtab. */
> for (ndst = i = 0; i < nsrc; i++) {
> if (i == 0 || is_livepatch_module(mod) ||
> - is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
> - info->index.pcpu)) {
> + is_core_symbol(src + i, info->sechdrs,
> info->hdr->e_shnum)) {
> strtab_size += strlen(&info->strtab[src[i].st_name])
> + 1;
> ndst++;
> }
> @@ -199,8 +193,7 @@ void add_kallsyms(struct module *mod, const struct
> load_info *info)
> for (ndst = i = 0; i < kallsyms->num_symtab; i++) {
> kallsyms->typetab[i] = elf_type(src + i, info);
> if (i == 0 || is_livepatch_module(mod) ||
> - is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
> - info->index.pcpu)) {
> + is_core_symbol(src + i, info->sechdrs,
> info->hdr->e_shnum)) {
> ssize_t ret;
>
> mod->core_kallsyms.typetab[ndst] =
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index c1b34dc1e89a..ae2678ac7840 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1619,12 +1619,13 @@ static int apply_relocations(struct module *mod,
> const struct load_info *info)
>
> /*
> * Don't bother with non-allocated sections.
> - * An exception is the percpu section, which has separate
> allocations
> - * for individual CPUs. We relocate the percpu section in the
> initial
> - * ELF template and subsequently copy it to the per-CPU
> destinations.
> + *
> + * Note that .data..percpu has separate allocations for
> + * individual CPUs. We relocate the section in the
> + * initial ELF template and subsequently copy it to the
> + * per-CPU destinations.
> */
> - if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC) &&
> - (!infosec || infosec != info->index.pcpu))
> + if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
> continue;
>
> if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
> @@ -1715,7 +1716,7 @@ static void __layout_sections(struct module *mod,
> struct load_info *info, bool i
>
> if ((s->sh_flags & masks[m][0]) != masks[m][0]
> || (s->sh_flags & masks[m][1])
> - || s->sh_entsize != ~0UL
> + || s->sh_entsize != ~0UL /* offset or standalone
> */
> || is_init != module_init_layout_section(sname))
> continue;
>
> @@ -1745,16 +1746,10 @@ static void __layout_sections(struct module *mod,
> struct load_info *info, bool i
> /*
> * Lay out the SHF_ALLOC sections in a way not dissimilar to how ld
> * might -- code, read-only data, read-write data, small data. Tally
> - * sizes, and place the offsets into sh_entsize fields: high bit means it
> - * belongs in init.
> + * sizes, and place the offsets into sh_entsize fields.
> */
> static void layout_sections(struct module *mod, struct load_info *info)
> {
> - unsigned int i;
> -
> - for (i = 0; i < info->hdr->e_shnum; i++)
> - info->sechdrs[i].sh_entsize = ~0UL;
> -
> pr_debug("Core section allocation order for %s:\n", mod->name);
> __layout_sections(mod, info, false);
>
> @@ -2822,7 +2817,8 @@ static int move_module(struct module *mod, struct
> load_info *info)
> Elf_Shdr *shdr = &info->sechdrs[i];
> const char *sname;
>
> - if (!(shdr->sh_flags & SHF_ALLOC))
> + if (!(shdr->sh_flags & SHF_ALLOC)
> + || shdr->sh_entsize == SH_ENTSIZE_STANDALONE)
> continue;
>
> sname = info->secstrings + shdr->sh_name;
> @@ -2954,6 +2950,7 @@ core_param(module_blacklist, module_blacklist, charp,
> 0400);
> static struct module *layout_and_allocate(struct load_info *info, int flags)
> {
> struct module *mod;
> + unsigned int i;
> int err;
>
> /* Allow arches to frob section contents and sizes. */
> @@ -2967,8 +2964,13 @@ static struct module *layout_and_allocate(struct
> load_info *info, int flags)
> if (err < 0)
> return ERR_PTR(err);
>
> + /* Repurpose sh_entsize to track where each section is allocated. */
> + for (i = 0; i < info->hdr->e_shnum; i++)
> + info->sechdrs[i].sh_entsize = ~0UL;
> +
> /* We will do a special allocation for per-cpu sections later. */
> - info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;
> + if (info->index.pcpu)
> + info->sechdrs[info->index.pcpu].sh_entsize =
> SH_ENTSIZE_STANDALONE;
>
> /*
> * Mark relevant sections as SHF_RO_AFTER_INIT so layout_sections()
> can
> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
> index 01c65d608873..15c6baeb39c4 100644
> --- a/kernel/module/sysfs.c
> +++ b/kernel/module/sysfs.c
> @@ -62,6 +62,15 @@ static void free_sect_attrs(struct module_sect_attrs
> *sect_attrs)
> kfree(sect_attrs);
> }
>
> +/*
> + * .data..percpu has a separate allocation per CPU and no single
> + * address to report.
> + */
> +static bool sect_visible(const struct load_info *info, unsigned int i)
> +{
> + return !sect_empty(&info->sechdrs[i]) && i != info->index.pcpu;
> +}
> +
> static int add_sect_attrs(struct module *mod, const struct load_info *info)
> {
> struct module_sect_attrs *sect_attrs;
> @@ -72,7 +81,7 @@ static int add_sect_attrs(struct module *mod, const struct
> load_info *info)
>
> /* Count loaded sections and allocate structures */
> for (i = 0; i < info->hdr->e_shnum; i++)
> - if (!sect_empty(&info->sechdrs[i]))
> + if (sect_visible(info, i))
> nloaded++;
> sect_attrs = kzalloc_flex(*sect_attrs, attrs, nloaded);
> if (!sect_attrs)
> @@ -92,7 +101,7 @@ static int add_sect_attrs(struct module *mod, const struct
> load_info *info)
> for (i = 0; i < info->hdr->e_shnum; i++) {
> Elf_Shdr *sec = &info->sechdrs[i];
>
> - if (sect_empty(sec))
> + if (!sect_visible(info, i))
> continue;
> sysfs_bin_attr_init(sattr);
> sattr->attr.name =
> @@ -159,7 +168,7 @@ static int add_notes_attrs(struct module *mod, const
> struct load_info *info)
> /* Count notes sections and allocate structures. */
> notes = 0;
> for (i = 0; i < info->hdr->e_shnum; i++)
> - if (!sect_empty(&info->sechdrs[i]) &&
> + if (sect_visible(info, i) &&
> info->sechdrs[i].sh_type == SHT_NOTE)
> ++notes;
>
> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const
> struct load_info *info)
>
> nattr = ¬es_attrs->attrs[0];
> for (loaded = i = 0; i < info->hdr->e_shnum; ++i) {
> - if (sect_empty(&info->sechdrs[i]))
> + if (!sect_visible(info, i))
> continue;
> if (info->sechdrs[i].sh_type == SHT_NOTE) {
> sysfs_bin_attr_init(nattr);
> --
> 2.25.1
>
