[RFC PATCH v2 08/24] unwind_user/eh_frame: Store .eh_frame_hdr section data in per-mm maple tree
From: Jens Remus
Date: Fri Aug 21 2026 - 15:59:01 EST
Associate .eh_frame_hdr sections with their mm by adding them to a
per-mm maple tree which is indexed by the corresponding text address
range. A single .eh_frame_hdr section can be associated with multiple
text ranges.
Based on Josh Poimboeuf's, Steven Rostedt's, and my unwind user sframe
implementation.
Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---
Notes (jremus):
Changes in RFC v2:
- INIT_MM_EH_FRAME and mm_init_eh_frame(): Use MT_FLAGS_USE_RCU to
enable concurrent eh_frame_mt read and write access. (Sashiko AI)
- eh_frame_remove_section(): Fix ABA problem by using the advanced
maple tree API to hold the internal spinlock while iterating over
the eh_frame_mt and removing the eh_frame section(s). (Sashiko AI)
arch/x86/include/asm/mmu.h | 2 +-
include/linux/eh_frame.h | 22 ++++++++++++
include/linux/mm_types.h | 3 ++
kernel/fork.c | 10 ++++++
kernel/unwind/eh_frame.c | 70 ++++++++++++++++++++++++++++++++++++--
mm/init-mm.c | 2 ++
6 files changed, 105 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 0fe9c569d171..227a32899a59 100644
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -87,7 +87,7 @@ typedef struct {
.context = { \
.ctx_id = 1, \
.lock = __MUTEX_INITIALIZER(mm.context.lock), \
- }
+ },
void leave_mm(void);
#define leave_mm leave_mm
diff --git a/include/linux/eh_frame.h b/include/linux/eh_frame.h
index aaac2dd663d5..c4279ee77c13 100644
--- a/include/linux/eh_frame.h
+++ b/include/linux/eh_frame.h
@@ -2,9 +2,14 @@
#ifndef _LINUX_EH_FRAME_H
#define _LINUX_EH_FRAME_H
+#include <linux/mm_types.h>
+#include <linux/srcu.h>
+
#ifdef CONFIG_HAVE_UNWIND_USER_EH_FRAME
struct eh_frame_section {
+ struct rcu_head rcu;
+
unsigned long eh_frame_hdr_start;
unsigned long eh_frame_hdr_end;
unsigned long text_start;
@@ -19,14 +24,29 @@ struct eh_frame_section {
u8 binary_search_table_enc;
};
+#define EH_FRAME_MT_FLAGS (MT_FLAGS_USE_RCU)
+
+#define INIT_MM_EH_FRAME .eh_frame_mt = MTREE_INIT(eh_frame_mt, EH_FRAME_MT_FLAGS),
+extern void eh_frame_free_mm(struct mm_struct *mm);
+
extern int eh_frame_add_section(unsigned long eh_frame_hdr_start,
unsigned long eh_frame_hdr_end,
unsigned long text_start,
unsigned long text_end);
extern int eh_frame_remove_section(unsigned long eh_frame_hdr_start);
+static inline bool current_has_eh_frame(void)
+{
+ struct mm_struct *mm = current->mm;
+
+ return mm && !mtree_empty(&mm->eh_frame_mt);
+}
+
#else /* !CONFIG_HAVE_UNWIND_USER_EH_FRAME */
+#define INIT_MM_EH_FRAME
+static inline void eh_frame_free_mm(struct mm_struct *mm) {}
+
static inline int eh_frame_add_section(unsigned long eh_frame_hdr_start,
unsigned long eh_frame_hdr_end,
unsigned long text_start,
@@ -40,6 +60,8 @@ static inline int eh_frame_remove_section(unsigned long eh_frame_hdr_start)
return -ENOSYS;
}
+static inline bool current_has_eh_frame(void) { return false; }
+
#endif /* CONFIG_HAVE_UNWIND_USER_EH_FRAME */
#endif /* _LINUX_EH_FRAME_H */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b18c2b2e7d2c..ac51d6212e86 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1404,6 +1404,9 @@ struct mm_struct {
#ifdef CONFIG_MM_ID
mm_id_t mm_id;
#endif /* CONFIG_MM_ID */
+#ifdef CONFIG_HAVE_UNWIND_USER_EH_FRAME
+ struct maple_tree eh_frame_mt;
+#endif
} __randomize_layout;
/*
diff --git a/kernel/fork.c b/kernel/fork.c
index f0e2e131a9a5..dab67d2eb096 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -111,6 +111,7 @@
#include <linux/tick.h>
#include <linux/unwind_deferred.h>
#include <linux/pgalloc.h>
+#include <linux/eh_frame.h>
#include <linux/uaccess.h>
#include <asm/mmu_context.h>
@@ -738,6 +739,7 @@ void __mmdrop(struct mm_struct *mm)
mm_pasid_drop(mm);
mm_destroy_cid(mm);
percpu_counter_destroy_many(mm->rss_stat, NR_MM_COUNTERS);
+ eh_frame_free_mm(mm);
free_mm(mm);
}
@@ -1082,6 +1084,13 @@ static void mmap_init_lock(struct mm_struct *mm)
#endif
}
+static void mm_init_eh_frame(struct mm_struct *mm)
+{
+#ifdef CONFIG_HAVE_UNWIND_USER_EH_FRAME
+ mt_init_flags(&mm->eh_frame_mt, EH_FRAME_MT_FLAGS);
+#endif
+}
+
static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
{
mt_init_flags(&mm->mm_mt, MM_MT_FLAGS);
@@ -1109,6 +1118,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
mm->pmd_huge_pte = NULL;
#endif
mm_init_uprobes_state(mm);
+ mm_init_eh_frame(mm);
hugetlb_count_init(mm);
futex_mm_init(mm);
diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c
index f25a0923e315..8cf19c5298fd 100644
--- a/kernel/unwind/eh_frame.c
+++ b/kernel/unwind/eh_frame.c
@@ -19,6 +19,8 @@
#define dbg(fmt, ...) \
pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
+DEFINE_STATIC_SRCU(eh_frame_srcu);
+
#define UNSAFE_GET_USER_INC(to, from, end, label) \
({ \
typeof(to) __to; \
@@ -310,6 +312,7 @@ int eh_frame_add_section(unsigned long eh_frame_hdr_start,
unsigned long text_start,
unsigned long text_end)
{
+ struct maple_tree *eh_frame_mt = ¤t->mm->eh_frame_mt;
struct mm_struct *mm = current->mm;
struct eh_frame_section *sec;
int ret;
@@ -352,15 +355,76 @@ int eh_frame_add_section(unsigned long eh_frame_hdr_start,
if (ret)
goto err_free;
- /* TODO nowhere to store it yet - just free it and return an error */
- ret = -ENOSYS;
+ ret = mtree_insert_range(eh_frame_mt, sec->text_start, sec->text_end - 1,
+ sec, GFP_KERNEL_ACCOUNT);
+ if (ret) {
+ dbg("mtree_insert_range failed: text=%lx-%lx\n",
+ sec->text_start, sec->text_end);
+ goto err_free;
+ }
+
+ return 0;
err_free:
free_section(sec);
return ret;
}
+static void eh_frame_free_srcu(struct rcu_head *rcu)
+{
+ struct eh_frame_section *sec = container_of(rcu, struct eh_frame_section, rcu);
+
+ free_section(sec);
+}
+
+static int __eh_frame_remove_section(struct ma_state *mas,
+ struct eh_frame_section *sec)
+{
+ if (mas_erase(mas) != sec) {
+ dbg("mas_erase failed: text=%lx\n", sec->text_start);
+ return -EINVAL;
+ }
+
+ call_srcu(&eh_frame_srcu, &sec->rcu, eh_frame_free_srcu);
+
+ return 0;
+}
+
int eh_frame_remove_section(unsigned long eh_frame_hdr_start)
{
- return -ENOSYS;
+ struct mm_struct *mm = current->mm;
+ struct eh_frame_section *sec;
+ MA_STATE(mas, &mm->eh_frame_mt, 0, 0);
+ bool found = false;
+ int ret = 0;
+
+ guard(srcu)(&eh_frame_srcu);
+
+ mtree_lock(&mm->eh_frame_mt);
+ mas_for_each(&mas, sec, ULONG_MAX) {
+ if (sec->eh_frame_hdr_start == eh_frame_hdr_start) {
+ found = true;
+ ret |= __eh_frame_remove_section(&mas, sec);
+ }
+ }
+ mtree_unlock(&mm->eh_frame_mt);
+
+ if (!found || ret)
+ return -EINVAL;
+
+ return 0;
+}
+
+void eh_frame_free_mm(struct mm_struct *mm)
+{
+ struct eh_frame_section *sec;
+ unsigned long index = 0;
+
+ if (!mm)
+ return;
+
+ mt_for_each(&mm->eh_frame_mt, sec, index, ULONG_MAX)
+ free_section(sec);
+
+ mtree_destroy(&mm->eh_frame_mt);
}
diff --git a/mm/init-mm.c b/mm/init-mm.c
index 3e792aad7626..25c26341fc4f 100644
--- a/mm/init-mm.c
+++ b/mm/init-mm.c
@@ -11,6 +11,7 @@
#include <linux/atomic.h>
#include <linux/user_namespace.h>
#include <linux/iommu.h>
+#include <linux/eh_frame.h>
#include <asm/mmu.h>
#ifndef INIT_MM_CONTEXT
@@ -48,6 +49,7 @@ struct mm_struct init_mm = {
#endif
.flexible_array = MM_STRUCT_FLEXIBLE_ARRAY_INIT,
INIT_MM_CONTEXT(init_mm)
+ INIT_MM_EH_FRAME
};
void setup_initial_init_mm(void *start_code, void *end_code,
--
2.53.0