[PATCH bpf-next v2 3/3] bpf/verifier: Take advantage of full allocation sizes

[Kees Cook <keescook@xxxxxxxxxxxx>]

Since the full kmalloc bucket size is being explicitly allocated, pass
back the resulting details to take advantage of the full size so that
reallocation checking will be needed less frequently.

Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 kernel/bpf/verifier.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1c040d27b8f6..e58b554e862b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1020,20 +1020,23 @@ static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t
 	return dst ? dst : ZERO_SIZE_PTR;
 }
 
-/* resize an array from old_n items to new_n items. the array is reallocated if it's too
- * small to hold new_n items. new items are zeroed out if the array grows.
+/* Resize an array from old_n items to *new_n items. The array is
+ * reallocated if it's too small to hold *new_n items. New items are
+ * zeroed out if the array grows. Allocation is rounded up to next kmalloc
+ * bucket size to reduce frequency of resizing. *new_n contains the new
+ * total number of items that will fit.
  *
- * Contrary to krealloc_array, does not free arr if new_n is zero.
+ * Contrary to krealloc, does not free arr if new_n is zero.
  */
-static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size)
+static void *realloc_array(void *arr, size_t old_n, size_t *new_n, size_t size)
 {
 	size_t alloc_size;
 	void *new_arr;
 
-	if (!new_n || old_n == new_n)
+	if (!new_n || !*new_n || old_n == *new_n)
 		goto out;
 
-	alloc_size = kmalloc_size_roundup(size_mul(new_n, size));
+	alloc_size = kmalloc_size_roundup(size_mul(*new_n, size));
 	new_arr = krealloc(arr, alloc_size, GFP_KERNEL);
 	if (!new_arr) {
 		kfree(arr);
@@ -1041,8 +1044,9 @@ static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size)
 	}
 	arr = new_arr;
 
-	if (new_n > old_n)
-		memset(arr + old_n * size, 0, (new_n - old_n) * size);
+	*new_n = alloc_size / size;
+	if (*new_n > old_n)
+		memset(arr + old_n * size, 0, (*new_n - old_n) * size);
 
 out:
 	return arr ? arr : ZERO_SIZE_PTR;
@@ -1074,7 +1078,7 @@ static int copy_stack_state(struct bpf_func_state *dst, const struct bpf_func_st
 
 static int resize_reference_state(struct bpf_func_state *state, size_t n)
 {
-	state->refs = realloc_array(state->refs, state->acquired_refs, n,
+	state->refs = realloc_array(state->refs, state->acquired_refs, &n,
 				    sizeof(struct bpf_reference_state));
 	if (!state->refs)
 		return -ENOMEM;
@@ -1090,11 +1094,12 @@ static int grow_stack_state(struct bpf_func_state *state, int size)
 	if (old_n >= n)
 		return 0;
 
-	state->stack = realloc_array(state->stack, old_n, n, sizeof(struct bpf_stack_state));
+	state->stack = realloc_array(state->stack, old_n, &n,
+				     sizeof(struct bpf_stack_state));
 	if (!state->stack)
 		return -ENOMEM;
 
-	state->allocated_stack = size;
+	state->allocated_stack = n * BPF_REG_SIZE;
 	return 0;
 }
 
-- 
2.34.1