From: Alan Maguire <alan.maguire@oracle.com>
Date: Fri, 16 Jul 2021 23:46:55 +0100
Subject: libbpf: Clarify/fix unaligned data issues for btf typed dump
Patch-mainline: v5.15-rc1
Git-commit: 8d44c3578b48d5f605eddcfd6a644e3944455a6b
References: jsc#PED-1377

If data is packed, data structures can store it outside of usual
boundaries.  For example a 4-byte int can be stored on a unaligned
boundary in a case like this:

struct s {
	char f1;
	int f2;
} __attribute((packed));

...the int is stored at an offset of one byte.  Some platforms have
problems dereferencing data that is not aligned with its size, and
code exists to handle most cases of this for BTF typed data display.
However pointer display was missed, and a simple function to test if
"ptr_is_aligned(data, data_sz)" would help clarify this code.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1626475617-25984-2-git-send-email-alan.maguire@oracle.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 tools/lib/bpf/btf_dump.c |   28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1654,6 +1654,11 @@ static int btf_dump_base_type_check_zero
 	return 0;
 }
 
+static bool ptr_is_aligned(const void *data, int data_sz)
+{
+	return ((uintptr_t)data) % data_sz == 0;
+}
+
 static int btf_dump_int_data(struct btf_dump *d,
 			     const struct btf_type *t,
 			     __u32 type_id,
@@ -1672,7 +1677,7 @@ static int btf_dump_int_data(struct btf_
 	/* handle packed int data - accesses of integers not aligned on
 	 * int boundaries can cause problems on some platforms.
 	 */
-	if (((uintptr_t)data) % sz)
+	if (!ptr_is_aligned(data, sz))
 		return btf_dump_bitfield_data(d, t, data, 0, 0);
 
 	switch (sz) {
@@ -1739,7 +1744,7 @@ static int btf_dump_float_data(struct bt
 	int sz = t->size;
 
 	/* handle unaligned data; copy to local union */
-	if (((uintptr_t)data) % sz) {
+	if (!ptr_is_aligned(data, sz)) {
 		memcpy(&fl, data, sz);
 		flp = &fl;
 	}
@@ -1892,12 +1897,27 @@ static int btf_dump_struct_data(struct b
 	return err;
 }
 
+union ptr_data {
+	unsigned int p;
+	unsigned long long lp;
+};
+
 static int btf_dump_ptr_data(struct btf_dump *d,
 			      const struct btf_type *t,
 			      __u32 id,
 			      const void *data)
 {
-	btf_dump_type_values(d, "%p", *(void **)data);
+	if (ptr_is_aligned(data, d->ptr_sz) && d->ptr_sz == sizeof(void *)) {
+		btf_dump_type_values(d, "%p", *(void **)data);
+	} else {
+		union ptr_data pt;
+
+		memcpy(&pt, data, d->ptr_sz);
+		if (d->ptr_sz == 4)
+			btf_dump_type_values(d, "0x%x", pt.p);
+		else
+			btf_dump_type_values(d, "0x%llx", pt.lp);
+	}
 	return 0;
 }
 
@@ -1910,7 +1930,7 @@ static int btf_dump_get_enum_value(struc
 	int sz = t->size;
 
 	/* handle unaligned enum value */
-	if (((uintptr_t)data) % sz) {
+	if (!ptr_is_aligned(data, sz)) {
 		*value = (__s64)btf_dump_bitfield_get_data(d, t, data, 0, 0);
 		return 0;
 	}