[PATCH v15 18/20] unwind_user/sframe: Duplicate registered .sframe section data on clone/fork

[Jens Remus]

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

Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---
 include/linux/sframe.h       |  5 ++++
 kernel/unwind/sframe.c       | 48 ++++++++++++++++++++++++++++++++++++
 kernel/unwind/sframe_debug.h |  7 ++++++
 mm/mmap.c                    |  9 +++++++
 4 files changed, 69 insertions(+)

diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index b79c5ec09229..91889b4fe3dd 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -28,6 +28,7 @@ struct sframe_section {
 };
 
 #define INIT_MM_SFRAME .sframe_mt = MTREE_INIT(sframe_mt, 0),
+extern int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm);
 extern void sframe_free_mm(struct mm_struct *mm);
 
 extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
@@ -45,6 +46,10 @@ static inline bool current_has_sframe(void)
 #else /* !CONFIG_HAVE_UNWIND_USER_SFRAME */
 
 #define INIT_MM_SFRAME
+static inline int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	return 0;
+}
 static inline void sframe_free_mm(struct mm_struct *mm) {}
 static inline int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 				     unsigned long text_start, unsigned long text_end)
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index ec8318977a2e..0661090dd5bc 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -886,6 +886,54 @@ int sframe_remove_section(unsigned long sframe_start)
 	return 0;
 }
 
+static void __sframe_dup_section(struct sframe_section *sec, struct sframe_section *oldsec)
+{
+	sec->sframe_start	= oldsec->sframe_start;
+	sec->sframe_end		= oldsec->sframe_end;
+	sec->text_start		= oldsec->text_start;
+	sec->text_end		= oldsec->text_end;
+
+	sec->fdes_start		= oldsec->fdes_start;
+	sec->fres_start		= oldsec->fres_start;
+	sec->fres_end		= oldsec->fres_end;
+	sec->num_fdes		= oldsec->num_fdes;
+
+	sec->ra_off		= oldsec->ra_off;
+	sec->fp_off		= oldsec->fp_off;
+
+	dbg_dup(sec, oldsec);
+}
+
+int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	struct sframe_section *sec, *oldsec;
+	unsigned long index = 0;
+	int ret;
+
+	guard(srcu)(&sframe_srcu);
+
+	mt_for_each(&oldmm->sframe_mt, oldsec, index, ULONG_MAX) {
+		sec = kzalloc(sizeof(*sec), GFP_KERNEL_ACCOUNT);
+		if (!sec)
+			return -ENOMEM;
+
+		__sframe_dup_section(sec, oldsec);
+
+		ret = mtree_insert_range(&mm->sframe_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 sframe_free_mm(struct mm_struct *mm)
 {
 	struct sframe_section *sec;
diff --git a/kernel/unwind/sframe_debug.h b/kernel/unwind/sframe_debug.h
index a63e75cccc70..2503972155e8 100644
--- a/kernel/unwind/sframe_debug.h
+++ b/kernel/unwind/sframe_debug.h
@@ -48,6 +48,12 @@ static inline void dbg_init(struct sframe_section *sec)
 		sec->filename = kstrdup("(anonymous)", GFP_KERNEL_ACCOUNT);
 }
 
+static inline void dbg_dup(struct sframe_section *sec, struct sframe_section *oldsec)
+{
+	if (oldsec->filename)
+		sec->filename = kstrdup(oldsec->filename, GFP_KERNEL_ACCOUNT);
+}
+
 static inline void dbg_free(struct sframe_section *sec)
 {
 	kfree(sec->filename);
@@ -61,6 +67,7 @@ static inline void dbg_free(struct sframe_section *sec)
 static inline void dbg_print_header(struct sframe_section *sec) {}
 
 static inline void dbg_init(struct sframe_section *sec) {}
+static inline void dbg_dup(struct sframe_section *sec, struct sframe_section *oldsec) {}
 static inline void dbg_free(struct sframe_section *sec) {}
 
 #endif /* !CONFIG_DYNAMIC_DEBUG */
diff --git a/mm/mmap.c b/mm/mmap.c
index 5754d1c36462..250e8bea73ef 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/sframe.h>
 
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
@@ -1846,6 +1847,11 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 	}
 	/* a new mm has just been created */
 	retval = arch_dup_mmap(oldmm, mm);
+#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
+	if (!retval) {
+		retval = sframe_dup_mm(mm, oldmm);
+	}
+#endif
 loop_out:
 	vma_iter_free(&vmi);
 	if (!retval) {
@@ -1893,6 +1899,9 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			vm_unacct_memory(charge);
 		}
 		__mt_destroy(&mm->mm_mt);
+#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
+		sframe_free_mm(mm);
+#endif
 		/*
 		 * 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
-- 
2.51.0