[PATCH v9 0/4] alloc_tag and module codetag section fixes

[PATCH v9 0/4] alloc_tag and module codetag section fixes

[Hao Ge]

I ran into an overflow problem in the module tag area. With profiling
toggled off, the overflow check in reserve_module_tags() 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. On overflow the fix shuts profiling down, releases
the reservation and returns -EAGAIN, and the codetag section lands
as regular module data in the same load, so the module loads without
profiling.

Review of the earlier series by Sashiko turned up two more problems.

One is a race. layout_sections() and move_module() both asked
codetag_needs_module_section() where a codetag section goes, and
mem_profiling_support can change between the two calls, for instance
when another module load overflows the tag index and shuts profiling
down. move_module() then copied the codetag section to offset 0 of
its regular destination and clobbered the first section placed in
that region.

v7 reworks where codetag sections are allocated, on a prototype by
Petr Pavlu [1]. The allocation runs before layout_sections() and the
placement is decided in one step, so nothing re-asks the question
and the race is gone. The retry is gone too, on -EAGAIN the section
is laid out as regular module data right in the same load.

[1] https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/

Following review feedback from Petr and Suren the series is now
split into four patches.

Patch 1 moves release_module_tags() above reserve_module_tags(),
since the failure paths now have to call it.

Patch 2 cleans up the populate failure path: the reservation is
released, module_tags.size rolled back and the PTEs a failed
vmap_pages_range() left behind unmapped, so a later populate of the
same range is safe. It carries both Fixes tags so it backports
wherever patch 4 goes, which uses its prev_size.

Patch 3 introduces SH_ENTSIZE_STANDALONE to mark sections with a
separate allocation, per the ELF spec SHF_ALLOC means a section
occupies memory during execution, and the percpu section does, only
outside the regular module layout. It was previously excluded from
the layout by clearing its SHF_ALLOC, overloading the flag with a
loader-internal meaning. The mark lives in sh_entsize now,
find_sec(".data..percpu") gives stable results again and
apply_relocations() goes back to testing only SHF_ALLOC. The section
would now show up under /sys/module/*/sections/, but it has one
instance per CPU and no single address to report, and the entry
never existed before, so add_sect_attrs() and add_notes_attrs()
skip it.

Patch 4 moves the codetag allocation out of move_module() in front
of layout_sections(). On overflow reserve_module_tags() shuts
profiling down, releases the reservation, rolls module_tags.size
back and returns -EAGAIN, and the section is laid out as regular
module data, so the module loads without profiling instead of
failing. Any other error fails the load. The release and the
fallback belong together, without the release rmmod hits the stale
entry and panics.

Tested on an x86_64 virtual machine:

Booted without sysctl.vm.mem_profiling=1,compressed:
# cat /proc/allocinfo is fine

Booted with sysctl.vm.mem_profiling=1,compressed:
# cat /proc/allocinfo is fine
# insmod overflow_tag.ko
# dmesg
  With module overflow_tag there are too many tags to fit in 13 page
  flag bits. Memory allocation profiling is disabled!
# rmmod overflow_tag
The module loads without profiling and unloads cleanly.

Changes in v9:
- do not export .data..percpu under /sys/module/*/sections/ (Petr
  Pavlu).
- move the populate failure cleanup in front of the rework, v8 patch
  4 is patch 2 now. It declares prev_size itself, which the overflow
  path of the rework also uses, so it carries both Fixes tags and the
  two patches backport together

Changes in v8:
- roll back module_tags.size when the reservation is released, so a
  concurrent load which already passed needs_section_mem() does not
  skip populate for the freed gap (Sashiko)
- unmap the PTEs a failed vmap_pages_range() installed, a retry to
  populate the same range would BUG on them
- zero the separately allocated codetag memory for an SHT_NOBITS
  section, the tag area pages are not zeroed on allocation (Sashiko)
- .data..percpu is exported under /sys/module/*/sections/ with the
  boot CPU instance of the per-cpu area, and the interface is
  documented in the ABI docs (Petr Pavlu)
- keep a comment in apply_relocations() on how .data..percpu is
  relocated (Petr Pavlu)
- replace the "Based-on-a-patch-by:" tag with an in-body
  attribution and a numbered Link: (Andrew Morton)

Changes in v7:
- split the rework following review feedback (Petr Pavlu, Suren
  Baghdasaryan)
- new patch 2 marks separately allocated sections with
  SH_ENTSIZE_STANDALONE instead of clearing SHF_ALLOC
  (suggested by Petr Pavlu)
- split the populate failure release into its own patch (suggested
  by Suren Baghdasaryan)

Changes in v6:
- rework on Petr's prototype and allocate codetag sections before
  layout_sections(), the retry and its state resets are gone
- fix the layout_sections()/move_module() race (Found by Sashiko)
- release the reservation on populate failure as well (Found by
  Sashiko)
- only -EAGAIN keeps the fallback, other errors fail the load

Changes in v5:
- add Fixes: and Cc: stable to patch 1/2 as well, since 2/2 does not
  compile without it (Andrew Morton)
- restore frob-adjusted mem[type].size on retry instead of zeroing,
  as s390 and parisc add GOT/PLT space there in
  module_frob_arch_sections() (Reported by Sashiko)
- drop the load_module() mem_profiling_support check; the percpu
  counter leak is pre-existing and orthogonal to this fix

Changes in v4:
- add a new patch (1/2) to move release_module_tags() above
  reserve_module_tags(); the overflow fix is 2/2
- release the reservation on the -EAGAIN path
- return -EAGAIN instead of -ENOMEM so the module can still load
  without profiling (Suren)
- reset sh_addr, mem[type].size and sym/str SHF_ALLOC before retry
- skip percpu counters in load_module() when profiling is off

Changes in v3:
- use pr_warn_once() instead of pr_warn()
- return -ENOMEM instead of -ENOSPC (Suren)
- expand the commit message to describe the /proc/allocinfo impact
  (Andrew)

Changes in v2:
- return an error after shutdown_mem_profiling() to skip
  vm_module_tags_populate()

v1: https://lore.kernel.org/all/20260804064408.105033-1-hao.ge@linux.dev/
v2: https://lore.kernel.org/all/20260804122038.190270-1-hao.ge@linux.dev/
v3: https://lore.kernel.org/all/20260805090633.141001-1-hao.ge@linux.dev/
v4: https://lore.kernel.org/all/20260810093955.153015-1-hao.ge@linux.dev/
v5: https://lore.kernel.org/all/20260812054105.102637-1-hao.ge@linux.dev/
v6: https://lore.kernel.org/all/20260831072104.120197-1-hao.ge@linux.dev/
v7: https://lore.kernel.org/all/20260902081802.146145-1-hao.ge@linux.dev/
v8: https://lore.kernel.org/all/20260907062414.106873-1-hao.ge@linux.dev/

Hao Ge (4):
  alloc_tag: move release_module_tags() above reserve_module_tags()
  alloc_tag: clean up the populate failure path
  module: introduce SH_ENTSIZE_STANDALONE for separately allocated
    sections
  module: allocate codetag sections before the regular module layout

 include/linux/module.h   |   2 +
 kernel/module/internal.h |   8 +++
 kernel/module/kallsyms.c |  13 +---
 kernel/module/main.c     | 133 +++++++++++++++++++++------------------
 kernel/module/sysfs.c    |  15 ++++-
 mm/alloc_tag.c           | 111 +++++++++++++++++---------------
 6 files changed, 158 insertions(+), 124 deletions(-)

-- 
2.25.1

[PATCH v9 1/4] alloc_tag: move release_module_tags() above reserve_module_tags()

[Hao Ge]

release_module_tags() is a cleanup helper. reserve_module_tags() can
also fail after storing the reservation in the maple tree, in which
case it should call release_module_tags() to undo it. Move the helper
above reserve_module_tags() so no forward declaration is needed.

No functional change.

Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Fixes: 0f9b685626da ("alloc_tag: populate memory for module tags as needed")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Cc: stable@vger.kernel.org
Acked-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
 mm/alloc_tag.c | 92 +++++++++++++++++++++++++-------------------------
 1 file changed, 46 insertions(+), 46 deletions(-)

diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index b1d48532a25a..e7a79116ad81 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -843,6 +843,52 @@ static int vm_module_tags_populate(void)
 	return 0;
 }
 
+static void release_module_tags(struct module *mod, bool used)
+{
+	MA_STATE(mas, &mod_area_mt, module_tags.size, module_tags.size);
+	struct alloc_tag *start_tag;
+	struct alloc_tag *end_tag;
+	struct module *val;
+
+	mas_lock(&mas);
+	mas_for_each_rev(&mas, val, 0)
+		if (val == mod)
+			break;
+
+	if (!val) /* module not found */
+		goto out;
+
+	if (!used)
+		goto release_area;
+
+	start_tag = (struct alloc_tag *)(module_tags.start_addr + mas.index);
+	end_tag = (struct alloc_tag *)(module_tags.start_addr + mas.last);
+	if (!clean_unused_counters(start_tag, end_tag)) {
+		struct alloc_tag *tag;
+
+		for (tag = start_tag; tag <= end_tag; tag++) {
+			struct alloc_tag_counters counter;
+
+			if (!tag->counters)
+				continue;
+
+			counter = alloc_tag_read(tag);
+			pr_info("%s:%u module %s func:%s has %llu allocated at module unload\n",
+				tag->ct.filename, tag->ct.lineno, tag->ct.modname,
+				tag->ct.function, counter.bytes);
+		}
+	} else {
+		used = false;
+	}
+release_area:
+	mas_store(&mas, used ? &unloaded_mod : NULL);
+	val = mas_prev_range(&mas, 0);
+	if (val == &prepend_mod)
+		mas_store(&mas, NULL);
+out:
+	mas_unlock(&mas);
+}
+
 static void *reserve_module_tags(struct module *mod, unsigned long size,
 				 unsigned int prepend, unsigned long align)
 {
@@ -930,52 +976,6 @@ static void *reserve_module_tags(struct module *mod, unsigned long size,
 	return (struct alloc_tag *)(module_tags.start_addr + offset);
 }
 
-static void release_module_tags(struct module *mod, bool used)
-{
-	MA_STATE(mas, &mod_area_mt, module_tags.size, module_tags.size);
-	struct alloc_tag *start_tag;
-	struct alloc_tag *end_tag;
-	struct module *val;
-
-	mas_lock(&mas);
-	mas_for_each_rev(&mas, val, 0)
-		if (val == mod)
-			break;
-
-	if (!val) /* module not found */
-		goto out;
-
-	if (!used)
-		goto release_area;
-
-	start_tag = (struct alloc_tag *)(module_tags.start_addr + mas.index);
-	end_tag = (struct alloc_tag *)(module_tags.start_addr + mas.last);
-	if (!clean_unused_counters(start_tag, end_tag)) {
-		struct alloc_tag *tag;
-
-		for (tag = start_tag; tag <= end_tag; tag++) {
-			struct alloc_tag_counters counter;
-
-			if (!tag->counters)
-				continue;
-
-			counter = alloc_tag_read(tag);
-			pr_info("%s:%u module %s func:%s has %llu allocated at module unload\n",
-				tag->ct.filename, tag->ct.lineno, tag->ct.modname,
-				tag->ct.function, counter.bytes);
-		}
-	} else {
-		used = false;
-	}
-release_area:
-	mas_store(&mas, used ? &unloaded_mod : NULL);
-	val = mas_prev_range(&mas, 0);
-	if (val == &prepend_mod)
-		mas_store(&mas, NULL);
-out:
-	mas_unlock(&mas);
-}
-
 static int load_module(struct module *mod, struct codetag *start, struct codetag *stop)
 {
 	/* Allocate module alloc_tag percpu counters */
-- 
2.25.1

[PATCH v9 2/4] alloc_tag: clean up the populate failure path

[Hao Ge]

The reservation is already stored in the maple tree when
vm_module_tags_populate() fails. A failed load never unloads the
module, so nothing releases the entry. Release it and roll
module_tags.size back. Without the rollback a concurrent load that
already passed needs_section_mem() can reuse the freed gap, skip
vm_module_tags_populate() and write to unmapped memory.

vmap_pages_range() may have installed some PTEs before failing. A
retry to populate the same range would BUG on them, so undo them,
but only if vmap actually ran.

Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Fixes: 0f9b685626da ("alloc_tag: populate memory for module tags as needed")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
 mm/alloc_tag.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index e7a79116ad81..e7a40a276ed9 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -812,6 +812,13 @@ static int vm_module_tags_populate(void)
 				     next_page, PAGE_SHIFT) < 0) {
 			release_pages_arg arg = { .pages = next_page };
 
+			/*
+			 * vmap_pages_range() only runs once all pages were
+			 * allocated, and it may have installed some mappings
+			 * before failing. Undo them.
+			 */
+			if (nr == more_pages)
+				vunmap_range(phys_end, phys_end + (nr << PAGE_SHIFT));
 			/* Clean up and error out */
 			release_pages(arg, nr);
 			return -ENOMEM;
@@ -955,6 +962,7 @@ static void *reserve_module_tags(struct module *mod, unsigned long size,
 		return ret;
 
 	if (module_tags.size < offset + size) {
+		unsigned long prev_size = module_tags.size;
 		int grow_res;
 
 		module_tags.size = offset + size;
@@ -969,6 +977,8 @@ static void *reserve_module_tags(struct module *mod, unsigned long size,
 			shutdown_mem_profiling(true);
 			pr_err("Failed to allocate memory for allocation tags in the module %s. Memory allocation profiling is disabled!\n",
 			       mod->name);
+			release_module_tags(mod, false);
+			module_tags.size = prev_size;
 			return ERR_PTR(grow_res);
 		}
 	}
-- 
2.25.1

[PATCH v9 3/4] module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections

[Hao Ge]

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.

Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1]
Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
 include/linux/module.h   |  2 ++
 kernel/module/internal.h |  8 ++++++++
 kernel/module/kallsyms.c | 13 +++----------
 kernel/module/main.c     | 32 +++++++++++++++++---------------
 kernel/module/sysfs.c    | 15 ++++++++++++---
 5 files changed, 42 insertions(+), 28 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,
 };
 
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 0fc11e45df9b..49190deae61e 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 c32f1d370b73..fc577c01dfd2 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1620,12 +1620,13 @@ 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)
@@ -1716,7 +1717,7 @@ 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;
 
@@ -1746,16 +1747,10 @@ 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);
 
@@ -2811,7 +2806,8 @@ 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;
@@ -2943,6 +2939,7 @@ 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.  */
@@ -2956,8 +2953,13 @@ 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..f64170344e69 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 =
@@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
 
 	nattr = &notes_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

Re: [PATCH v9 3/4] module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections

[Petr Pavlu]

On 9/8/26 11:24 AM, Hao Ge 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.
> 
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1]
> Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Hao Ge <hao.ge@linux.dev>
> ---
> [...]
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index 0fc11e45df9b..49190deae61e 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] =

FTR These changes in kernel/module/kallsyms.c have a conflict with the
series "Ignore local labels and mapping symbols during module load" [1],
which is currently queued on modules-next, but it should be
straightforward to resolve.

> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
> index 01c65d608873..f64170344e69 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 =
> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
>  
>  	nattr = &notes_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);

add_notes_attrs() has two sect_empty() calls. Both should be changed to
sect_visible().

With this fixed, the patch looks ok to me. Feel free to add:

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

[1] https://lore.kernel.org/linux-modules/20260820125007.22943-1-yangtiezhu@loongson.cn/

-- 
Thanks,
Petr

Re: [PATCH v9 3/4] module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections

[Hao Ge]

Hi Petr


On 9/9/26 19:30, Petr Pavlu wrote:
> On 9/8/26 11:24 AM, Hao Ge 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.
>>
>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
>> Reported-by: Sashiko <sashiko-bot@kernel.org>
>> Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1]
>> Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Hao Ge <hao.ge@linux.dev>
>> ---
>> [...]
>> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
>> index 0fc11e45df9b..49190deae61e 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] =
> FTR These changes in kernel/module/kallsyms.c have a conflict with the
> series "Ignore local labels and mapping symbols during module load" [1],
> which is currently queued on modules-next, but it should be
> straightforward to resolve.
>
>> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
>> index 01c65d608873..f64170344e69 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 =
>> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
>>   
>>   	nattr = &notes_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);
> add_notes_attrs() has two sect_empty() calls. Both should be changed to
> sect_visible().


I kept this part unmodified to preserve the loop's original intent.

This loop counts SHT_NOTE sections.

SHT_NOTE refers to ELF note sections, which hold non-executable

metadata such as build ID and ABI info.

I wonder if we could keep the current implementation.

As noted in the comment above, the top part counts SHT_NOTE sections

and allocates structures, while the lower logic handles control of node 
attributes.


WDYT?


Thanks

Best Regards

Hao

>
> With this fixed, the patch looks ok to me. Feel free to add:
>
> Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
>
> [1] https://lore.kernel.org/linux-modules/20260820125007.22943-1-yangtiezhu@loongson.cn/
>

Re: [PATCH v9 3/4] module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections

[Hao Ge]

On 9/9/26 20:47, Hao Ge wrote:
> Hi Petr
>
>
> On 9/9/26 19:30, Petr Pavlu wrote:
>> On 9/8/26 11:24 AM, Hao Ge 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.
>>>
>>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag 
>>> compression")
>>> Reported-by: Sashiko <sashiko-bot@kernel.org>
>>> Link: 
>>> https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ 
>>> [1]
>>> Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Hao Ge <hao.ge@linux.dev>
>>> ---
>>> [...]
>>> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
>>> index 0fc11e45df9b..49190deae61e 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] =
>> FTR These changes in kernel/module/kallsyms.c have a conflict with the
>> series "Ignore local labels and mapping symbols during module load" [1],
>> which is currently queued on modules-next, but it should be
>> straightforward to resolve.
>>
>>> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
>>> index 01c65d608873..f64170344e69 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 =
>>> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, 
>>> const struct load_info *info)
>>>         nattr = &notes_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);
>> add_notes_attrs() has two sect_empty() calls. Both should be changed to
>> sect_visible().
>
>
> I kept this part unmodified to preserve the loop's original intent.
>
> This loop counts SHT_NOTE sections.
>
> SHT_NOTE refers to ELF note sections, which hold non-executable
>
> metadata such as build ID and ABI info.
>
> I wonder if we could keep the current implementation.
>
> As noted in the comment above, the top part counts SHT_NOTE sections
>
> and allocates structures, while the lower logic handles control of 
> node attributes.
>
>
> WDYT?
>
>

Sorry, I've reconsidered this. I think changing it to sect_visible would 
be better.

sect_visible stands for the count of externally visible note attributes, 
so the code

above and below can align with each other.


Sorry for the noise.


I'll rebase onto modules-next, apply this change and push a new revision.

I'll also add your Reviewed-by tag.


Thanks

Best Regards

Hao


> Thanks
>
> Best Regards
>
> Hao
>
>>
>> With this fixed, the patch looks ok to me. Feel free to add:
>>
>> Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
>>
>> [1] 
>> https://lore.kernel.org/linux-modules/20260820125007.22943-1-yangtiezhu@loongson.cn/
>>

Re: [PATCH v9 3/4] module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections

[Petr Pavlu]

On 9/9/26 3:08 PM, Hao Ge wrote:
> On 9/9/26 20:47, Hao Ge wrote:
>> On 9/9/26 19:30, Petr Pavlu wrote:
>>> On 9/8/26 11:24 AM, Hao Ge 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.
>>>>
>>>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
>>>> Reported-by: Sashiko <sashiko-bot@kernel.org>
>>>> Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1]
>>>> Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
>>>> Cc: stable@vger.kernel.org
>>>> Signed-off-by: Hao Ge <hao.ge@linux.dev>
>>>> ---
>>>> [...]
>>>> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
>>>> index 0fc11e45df9b..49190deae61e 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] =
>>> FTR These changes in kernel/module/kallsyms.c have a conflict with the
>>> series "Ignore local labels and mapping symbols during module load" [1],
>>> which is currently queued on modules-next, but it should be
>>> straightforward to resolve.
>>>
>>>> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
>>>> index 01c65d608873..f64170344e69 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 =
>>>> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
>>>>         nattr = &notes_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);
>>> add_notes_attrs() has two sect_empty() calls. Both should be changed to
>>> sect_visible().
>>
>>
>> I kept this part unmodified to preserve the loop's original intent.
>>
>> This loop counts SHT_NOTE sections.
>>
>> SHT_NOTE refers to ELF note sections, which hold non-executable
>>
>> metadata such as build ID and ABI info.
>>
>> I wonder if we could keep the current implementation.
>>
>> As noted in the comment above, the top part counts SHT_NOTE sections
>>
>> and allocates structures, while the lower logic handles control of node attributes.
>>
>>
>> WDYT?
>>
>>
> 
> Sorry, I've reconsidered this. I think changing it to sect_visible would be better.
> 
> sect_visible stands for the count of externally visible note attributes, so the code
> 
> above and below can align with each other.
> 
> 
> Sorry for the noise.

No worries.

One problem with continuing to use sect_empty() in the first loop is
that it could overallocate the number of required entries if a module
contains an SHT_NOTE section named .data..percpu. That shouldn't happen,
but we can trivially avoid it by using sect_visible() there as well.

Using the same condition in both loops also makes the code generally
simpler to understand.

-- 
Cheers,
Petr

[PATCH v9 4/4] module: allocate codetag sections before the regular module layout

[Hao Ge]

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 reservation is released and
module_tags.size rolled back, so a concurrent load which already
passed needs_section_mem() does not skip vm_module_tags_populate()

An SHT_NOBITS codetag section is zeroed explicitly, the tag area
pages are not zeroed on allocation.

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().

Based on a patch by Petr Pavlu [1].

Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1]
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
 kernel/module/main.c | 101 +++++++++++++++++++++++--------------------
 mm/alloc_tag.c       |   9 ++--
 2 files changed, 60 insertions(+), 50 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index fc577c01dfd2..af8880d430fb 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1724,20 +1724,6 @@ static void __layout_sections(struct module *mod, struct load_info *info, bool i
 			if (WARN_ON_ONCE(type == MOD_INVALID))
 				continue;
 
-			/*
-			 * Do not allocate codetag memory as we load it into
-			 * preallocated contiguous memory.
-			 */
-			if (codetag_needs_module_section(mod, sname, s->sh_size)) {
-				/*
-				 * s->sh_entsize won't be used but populate the
-				 * type field to avoid confusion.
-				 */
-				s->sh_entsize = ((unsigned long)(type) & SH_ENTSIZE_TYPE_MASK)
-						<< SH_ENTSIZE_TYPE_SHIFT;
-				continue;
-			}
-
 			s->sh_entsize = module_get_offset_and_type(mod, type, s, i);
 			pr_debug("\t%s\n", sname);
 		}
@@ -2784,7 +2770,6 @@ static int move_module(struct module *mod, struct load_info *info)
 {
 	int i, ret;
 	enum mod_mem_type t = MOD_MEM_NUM_TYPES;
-	bool codetag_section_found = false;
 
 	for_each_mod_mem_type(type) {
 		if (!mod->mem[type].size) {
@@ -2804,35 +2789,13 @@ static int move_module(struct module *mod, struct load_info *info)
 	for (i = 0; i < info->hdr->e_shnum; i++) {
 		void *dest;
 		Elf_Shdr *shdr = &info->sechdrs[i];
-		const char *sname;
 
 		if (!(shdr->sh_flags & SHF_ALLOC)
 		    || shdr->sh_entsize == SH_ENTSIZE_STANDALONE)
 			continue;
 
-		sname = info->secstrings + shdr->sh_name;
-		/*
-		 * Load codetag sections separately as they might still be used
-		 * after module unload.
-		 */
-		if (codetag_needs_module_section(mod, sname, shdr->sh_size)) {
-			dest = codetag_alloc_module_section(mod, sname, shdr->sh_size,
-					arch_mod_section_prepend(mod, i), shdr->sh_addralign);
-			if (WARN_ON(!dest)) {
-				ret = -EINVAL;
-				goto out_err;
-			}
-			if (IS_ERR(dest)) {
-				ret = PTR_ERR(dest);
-				goto out_err;
-			}
-			codetag_section_found = true;
-		} else {
-			enum mod_mem_type type = shdr->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT;
-			unsigned long offset = shdr->sh_entsize & SH_ENTSIZE_OFFSET_MASK;
-
-			dest = mod->mem[type].base + offset;
-		}
+		dest = mod->mem[shdr->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT].base +
+		       (shdr->sh_entsize & SH_ENTSIZE_OFFSET_MASK);
 
 		if (shdr->sh_type != SHT_NOBITS) {
 			/*
@@ -2864,8 +2827,6 @@ static int move_module(struct module *mod, struct load_info *info)
 	module_memory_restore_rox(mod);
 	while (t--)
 		module_memory_free(mod, t);
-	if (codetag_section_found)
-		codetag_free_module_sections(mod);
 
 	return ret;
 }
@@ -2936,6 +2897,49 @@ static bool blacklisted(const char *module_name)
 }
 core_param(module_blacklist, module_blacklist, charp, 0400);
 
+/*
+ * Allocate codetag sections separately. They are loaded into preallocated
+ * contiguous memory because they may still be used after the module is
+ * unloaded.
+ *
+ * If the separate allocation overflows, allocate the section normally
+ * so that the module can still be loaded.
+ */
+static int allocate_codetag_sections(struct load_info *info)
+{
+	for (unsigned int i = 1; i < info->hdr->e_shnum; i++) {
+		Elf_Shdr *shdr = &info->sechdrs[i];
+		const char *sname = info->secstrings + shdr->sh_name;
+		void *dest;
+
+		if (!codetag_needs_module_section(info->mod, sname, shdr->sh_size))
+			continue;
+
+		dest = codetag_alloc_module_section(info->mod, sname, shdr->sh_size,
+				arch_mod_section_prepend(info->mod, i), shdr->sh_addralign);
+		if (WARN_ON(!dest)) {
+			codetag_free_module_sections(info->mod);
+			return -EINVAL;
+		}
+		if (dest == ERR_PTR(-EAGAIN))
+			/* Allocate the section as a regular section. */
+			continue;
+		if (IS_ERR(dest)) {
+			codetag_free_module_sections(info->mod);
+			return PTR_ERR(dest);
+		}
+
+		if (shdr->sh_type != SHT_NOBITS)
+			memcpy(dest, (void *)shdr->sh_addr, shdr->sh_size);
+		else
+			memset(dest, 0, shdr->sh_size);
+		shdr->sh_addr = (unsigned long)dest;
+		shdr->sh_entsize = SH_ENTSIZE_STANDALONE;
+	}
+
+	return 0;
+}
+
 static struct module *layout_and_allocate(struct load_info *info, int flags)
 {
 	struct module *mod;
@@ -2968,18 +2972,21 @@ 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)
+		return ERR_PTR(err);
+
+	/* Determine total sizes and put offsets in sh_entsize. */
 	layout_sections(info->mod, info);
 	layout_symtab(info->mod, info);
 
 	/* Allocate and move to the final place */
 	err = move_module(info->mod, info);
-	if (err)
+	if (err) {
+		codetag_free_module_sections(info->mod);
 		return ERR_PTR(err);
+	}
 
 	/* Module has been copied to its final place now: return it. */
 	mod = (void *)info->sechdrs[info->index.mod].sh_addr;
diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index e7a40a276ed9..76942f2e3905 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -966,10 +966,13 @@ static void *reserve_module_tags(struct module *mod, unsigned long size,
 		int grow_res;
 
 		module_tags.size = offset + size;
-		if (mem_alloc_profiling_enabled() && !tags_addressable()) {
+		if (!tags_addressable()) {
 			shutdown_mem_profiling(true);
-			pr_warn("With module %s there are too many tags to fit in %d page flag bits. Memory allocation profiling is disabled!\n",
-				mod->name, NR_UNUSED_PAGEFLAG_BITS);
+			pr_warn_once("With module %s there are too many tags to fit in %d page flag bits. Memory allocation profiling is disabled!\n",
+				     mod->name, NR_UNUSED_PAGEFLAG_BITS);
+			release_module_tags(mod, false);
+			module_tags.size = prev_size;
+			return ERR_PTR(-EAGAIN);
 		}
 
 		grow_res = vm_module_tags_populate();
-- 
2.25.1

Re: [PATCH v9 4/4] module: allocate codetag sections before the regular module layout

[Petr Pavlu]

On 9/8/26 11:24 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 reservation is released and
> module_tags.size rolled back, so a concurrent load which already
> passed needs_section_mem() does not skip vm_module_tags_populate()
> 
> An SHT_NOBITS codetag section is zeroed explicitly, the tag area
> pages are not zeroed on allocation.
> 
> 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().
> 
> Based on a patch by Petr Pavlu [1].
> 
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1]
> Cc: stable@vger.kernel.org
> Signed-off-by: Hao Ge <hao.ge@linux.dev>

This looks ok to me from the module loader's perspective.

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

-- 
Thanks,
Petr