Re: [RFC PATCH v6 2/2] module: allocate codetag sections before the regular module layout

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 <sashiko-bot@kernel.org>
Based-on-a-patch-by: Petr Pavlu [off-list ref]
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
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,
 };
 

@@ -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);