On 8/31/26 9:21 AM, Hao Ge wrote:
> Whether a codetag section goes to the codetag region is decided by
> layout_sections() and asked again in move_module(). A concurrent
> load can shut profiling down in between, and move_module() then
> copies the section to offset 0 of its regular destination,
> overwriting whatever is there.
>
> Decide and allocate in one pass, before the layout. Allocation
> errors fail the load. On a tag area overflow profiling is already
> disabled, so -EAGAIN makes the section fall back to regular module
> data and the module still loads.
>
> The overflow and populate failure paths of reserve_module_tags() now
> release their reservation instead of leaking the maple tree entry.
> When profiling was toggled off, the overflow check did not run, a
> module could load with more tags than the page flags can address,
> and re-enabling profiling then silently corrupted /proc/allocinfo.
> The check no longer depends on mem_alloc_profiling_enabled().
>
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Reported-by: Sashiko <[email protected]>
> Based-on-a-patch-by: Petr Pavlu <[email protected]>
> Cc: Suren Baghdasaryan <[email protected]>
> Signed-off-by: Hao Ge <[email protected]>
> ---
> Changes against Petr's prototype:
> - allocate_codetag_sections() returns an error instead of void, and
> only -EAGAIN falls back to a regular section. Any other error now
> fails the load. The prototype fell back on everything, which can
> leave live tags in module memory.
> - reserve_module_tags() releases its reservation when populate fails
> too, that path used to leak the maple tree entry.
> - codetag_free_module_sections() on the move_module() error path uses
> info->mod, the local mod is assigned only after a successful move.
> - The percpu section is marked only when index.pcpu != 0, otherwise
> sechdrs[0] gets marked.
> - Dropped the SHF_ALLOC check, .codetag.* sections always have it.
> ---
> include/linux/module.h | 2 +
> kernel/module/internal.h | 4 ++
> kernel/module/main.c | 120 ++++++++++++++++++++-------------------
> mm/alloc_tag.c | 9 ++-
> 4 files changed, 75 insertions(+), 60 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 7566815fabbe..33548daa31a3 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,
> };
>
It might be better to split this patch into two: the first to introduce
MOD_STANDALONE and use it only for the percpu section, and the second
with all the codetag-related changes.
The introduction of SH_ENTSIZE_STANDALONE should also allow us to clean
up the current resetting of SHF_ALLOC for the percpu section, and now
also for codetag sections. The problem is that find_sec(".data..percpu")
can currently return different results depending on whether it is called
before layout_and_allocate() or later. In addition, apply_relocations()
needs a special case for SH_ENTSIZE_STANDALONE, where it could otherwise
just test SHF_ALLOC.
Instead of resetting SHF_ALLOC for percpu/codetag sections, both
__layout_sections() and move_module() can check for
SH_ENTSIZE_STANDALONE to determine whether a section is handled
specially and should be skipped.
I think it would be useful to include this change in the first patch
introducing MOD_STANDALONE, but I'm also ok with the current version.
I can send a separate patch later to make more use of
SH_ENTSIZE_STANDALONE in this way.
> @@ -2966,18 +2967,23 @@ static struct module *layout_and_allocate(struct
> load_info *info, int flags)
> */
> module_mark_ro_after_init(info->hdr, info->sechdrs, info->secstrings);
>
> - /*
> - * Determine total sizes, and put offsets in sh_entsize. For now
> - * this is done generically; there doesn't appear to be any
> - * special cases for the architectures.
> - */
> + /* Allow codetag sections to be allocated separately first. */
> + err = allocate_codetag_sections(info);
> + if (err) {
> + codetag_free_module_sections(info->mod);
The usual convention is that functions clean up after themselves on
error. That means this codetag_free_module_sections() call should be
done ideally by allocate_codetag_sections().
--
Thanks,
Petr
