[RFC PATCH v1 15/25] unwind_user/eh_frame: Duplicate registered .eh_frame[_hdr] section data on clone/fork

[Jens Remus]

When duplicating a process' virtual memory mappings also duplicate all
of its registered .eh_frame_hdr sections stored in the per-mm maple tree
to enable stacktracing using eh_frame of the child process.

Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---
 include/linux/eh_frame.h       |  7 +++++
 kernel/unwind/eh_frame.c       | 48 ++++++++++++++++++++++++++++++++++
 kernel/unwind/eh_frame_debug.h |  7 +++++
 mm/mmap.c                      |  5 ++++
 4 files changed, 67 insertions(+)

diff --git a/include/linux/eh_frame.h b/include/linux/eh_frame.h
index b2f98cd6166f..65f87c2714d8 100644
--- a/include/linux/eh_frame.h
+++ b/include/linux/eh_frame.h
@@ -30,6 +30,7 @@ struct eh_frame_section {
 };
 
 #define INIT_MM_EH_FRAME .eh_frame_mt = MTREE_INIT(eh_frame_mt, 0),
+extern int eh_frame_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm);
 extern void eh_frame_free_mm(struct mm_struct *mm);
 
 extern int eh_frame_add_section(unsigned long eh_frame_hdr_start,
@@ -49,6 +50,12 @@ static inline bool current_has_eh_frame(void)
 #else /* !CONFIG_HAVE_UNWIND_USER_EH_FRAME */
 
 #define INIT_MM_EH_FRAME
+
+static inline int eh_frame_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	return 0;
+}
+
 static inline void eh_frame_free_mm(struct mm_struct *mm) {}
 
 static inline int eh_frame_add_section(unsigned long eh_frame_hdr_start,
diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c
index c9161229196c..7f572d1711d3 100644
--- a/kernel/unwind/eh_frame.c
+++ b/kernel/unwind/eh_frame.c
@@ -1450,6 +1450,54 @@ int eh_frame_remove_section(unsigned long eh_frame_hdr_start)
 	return 0;
 }
 
+static void __eh_frame_dup_section(struct eh_frame_section *sec,
+				   struct eh_frame_section *oldsec)
+{
+	sec->eh_frame_hdr_start	= oldsec->eh_frame_hdr_start;
+	sec->eh_frame_hdr_end	= oldsec->eh_frame_hdr_end;
+	sec->text_start		= oldsec->text_start;
+	sec->text_end		= oldsec->text_end;
+
+	sec->eh_frame_start		= oldsec->eh_frame_start;
+	sec->eh_frame_vma_end		= oldsec->eh_frame_vma_end;
+	sec->binary_search_table_start	= oldsec->binary_search_table_start;
+	sec->binary_search_table_end	= oldsec->binary_search_table_end;
+	sec->fde_count			= oldsec->fde_count;
+	sec->binary_search_table_enc	= oldsec->binary_search_table_enc;
+
+	dbg_dup(sec, oldsec);
+}
+
+int eh_frame_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	struct eh_frame_section *sec, *oldsec;
+	unsigned long index = 0;
+	int ret;
+
+	guard(srcu)(&eh_frame_srcu);
+
+	mt_for_each(&oldmm->eh_frame_mt, oldsec, index, ULONG_MAX) {
+		sec = kzalloc(sizeof(*sec), GFP_KERNEL_ACCOUNT);
+		if (!sec)
+			return -ENOMEM;
+
+		__eh_frame_dup_section(sec, oldsec);
+
+		ret = mtree_insert_range(&mm->eh_frame_mt,
+					 sec->text_start,
+					 sec->text_end - 1,
+					 sec, GFP_KERNEL_ACCOUNT);
+		if (ret)
+			goto err_free;
+	}
+
+	return 0;
+
+err_free:
+	free_section(sec);
+	return ret;
+}
+
 void eh_frame_free_mm(struct mm_struct *mm)
 {
 	struct eh_frame_section *sec;
diff --git a/kernel/unwind/eh_frame_debug.h b/kernel/unwind/eh_frame_debug.h
index bcb2d03ab9ab..e72e011ba539 100644
--- a/kernel/unwind/eh_frame_debug.h
+++ b/kernel/unwind/eh_frame_debug.h
@@ -41,6 +41,12 @@ static inline void dbg_init(struct eh_frame_section *sec)
 		sec->filename = kstrdup("(vma unknown???)", GFP_KERNEL_ACCOUNT);
 }
 
+static inline void dbg_dup(struct eh_frame_section *sec, struct eh_frame_section *oldsec)
+{
+	if (oldsec->filename)
+		sec->filename = kstrdup(oldsec->filename, GFP_KERNEL_ACCOUNT);
+}
+
 static inline void dbg_free(struct eh_frame_section *sec)
 {
 	kfree(sec->filename);
@@ -53,6 +59,7 @@ static inline void dbg_free(struct eh_frame_section *sec)
 #define dbg_sec_ehfh(args...)		no_printk(args)
 
 static inline void dbg_init(struct eh_frame_section *sec) {}
+static inline void dbg_dup(struct eh_frame_section *sec, struct eh_frame_section *oldsec) {}
 static inline void dbg_free(struct eh_frame_section *sec) {}
 
 #endif /* !CONFIG_DYNAMIC_DEBUG */
diff --git a/mm/mmap.c b/mm/mmap.c
index 2311ae7c2ff4..7715a799810e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -48,6 +48,7 @@
 #include <linux/sched/mm.h>
 #include <linux/ksm.h>
 #include <linux/memfd.h>
+#include <linux/eh_frame.h>
 
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
@@ -1844,6 +1845,9 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			goto loop_out;
 		}
 	}
+	retval = eh_frame_dup_mm(mm, oldmm);
+	if (retval)
+		goto loop_out;
 	/* a new mm has just been created */
 	retval = arch_dup_mmap(oldmm, mm);
 loop_out:
@@ -1893,6 +1897,7 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			vm_unacct_memory(charge);
 		}
 		__mt_destroy(&mm->mm_mt);
+		eh_frame_free_mm(mm);
 		/*
 		 * The mm_struct is going to exit, but the locks will be dropped
 		 * first.  Set the mm_struct as unstable is advisable as it is
-- 
2.53.0