On 4/11/24 15:13, Eduard Zingerman wrote:
On Tue, 2024-04-09 at 17:41 -0700, Kui-Feng Lee wrote:
Previously, check_map_kptr_access() assumed that the accessed offset was
identical to the offset in the btf_field. However, once field array is
supported, the accessed offset no longer matches the offset in the
bpf_field. It may refer to an element in an array while the offset in the
bpf_field refers to the beginning of the array.
To handle arrays, it computes the offset from the reg state instead.
Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
---
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
kernel/bpf/verifier.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 86adacc5f76c..34e43220c6f0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5349,18 +5349,19 @@ static u32 btf_ld_kptr_type(struct bpf_verifier_env *env, struct btf_field *kptr
}
static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
- int value_regno, int insn_idx,
+ u32 offset, int value_regno, int insn_idx,
struct btf_field *kptr_field)
{
struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
int class = BPF_CLASS(insn->code);
- struct bpf_reg_state *val_reg;
+ struct bpf_reg_state *val_reg, *reg;
/* Things we already checked for in check_map_access and caller:
Nit: at the moment when this patch is applied check_map_access is not
yet modified.
Yes, I will change the order of the patches.
* - Reject cases where variable offset may touch kptr
* - size of access (must be BPF_DW)
* - tnum_is_const(reg->var_off)
- * - kptr_field->offset == off + reg->var_off.value
+ * - kptr_field->offset + kptr_field->size * i / kptr_field->nelems
+ * == off + reg->var_off.value where n is an index into the array
^^^ nit: this should be 'i'
Yes!
*/
/* Only BPF_[LDX,STX,ST] | BPF_MEM | BPF_DW is supported */
if (BPF_MODE(insn->code) != BPF_MEM) {
[...]
