[PATCH v2] powerpc/kexec: Annotate umem_info members with __counted_by_ptr()

[Thorsten Blum <blum@kernel.org>]

Add __counted_by_ptr() to umem_info::buf and umem_info::ranges to
improve access bounds checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

In check_realloc_usable_mem(), return early on krealloc() failure and
use sizeof(*buf) when deriving max_entries from the allocation size.

Signed-off-by: Thorsten Blum <blum@kernel.org>
---
Changes in v2:
- Preserve the original pointer/count assignment order (Sourabh Jain)
- v1: https://lore.kernel.org/r/20260730130248.597249-2-thorsten.blum@linux.dev/
---
 arch/powerpc/kexec/file_load_64.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index bd80c5fb1b1f..7f45493e7c7a 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -34,14 +34,14 @@
 #include <asm/cputhreads.h>
 
 struct umem_info {
-	__be64 *buf;		/* data buffer for usable-memory property */
+	__be64 *buf __counted_by_ptr(max_entries); /* data buffer for usable-memory property */
 	u32 size;		/* size allocated for the data buffer */
 	u32 max_entries;	/* maximum no. of entries */
 	u32 idx;		/* index of current entry */
 
 	/* usable memory ranges to look up */
 	unsigned int nr_ranges;
-	const struct range *ranges;
+	const struct range *ranges __counted_by_ptr(nr_ranges);
 };
 
 const struct kexec_file_ops * const kexec_file_loaders[] = {
@@ -83,11 +83,12 @@ static __be64 *check_realloc_usable_mem(struct umem_info *um_info, int cnt)
 
 	new_size = um_info->size + MEM_RANGE_CHUNK_SZ;
 	tbuf = krealloc(um_info->buf, new_size, GFP_KERNEL);
-	if (tbuf) {
-		um_info->buf = tbuf;
-		um_info->size = new_size;
-		um_info->max_entries = (um_info->size / sizeof(u64));
-	}
+	if (!tbuf)
+		return NULL;
+
+	um_info->buf = tbuf;
+	um_info->size = new_size;
+	um_info->max_entries = um_info->size / sizeof(*um_info->buf);
 
 	return tbuf;
 }
@@ -288,12 +289,12 @@ static int update_usable_mem_fdt(void *fdt, struct crash_mem *usable_mem)
 		return -EINVAL;
 	}
 
-	um_info.buf  = NULL;
+	um_info.buf = NULL;
 	um_info.size = 0;
 	um_info.max_entries = 0;
-	um_info.idx  = 0;
+	um_info.idx = 0;
 	/* Memory ranges to look up */
-	um_info.ranges = &(usable_mem->ranges[0]);
+	um_info.ranges = usable_mem->ranges;
 	um_info.nr_ranges = usable_mem->nr_ranges;
 
 	dn = of_find_node_by_path("/ibm,dynamic-reconfiguration-memory");