Hi Suren
On 2026/9/18 01:25, Suren Baghdasaryan wrote:
> 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?
>
Right, I'll fold this into the commit message for the next version:
"No functional or userspace-visible changes otherwise."
>>
>> 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]>
>
Thanks.
Best Regards
Hao
>> ---
>> 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
>>
