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-rw-r--r--kernel/bpf/verifier.c23
1 files changed, 14 insertions, 9 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3fb50757e812..315798037d6c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1772,16 +1772,21 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno,
bitmap_from_u64(mask, stack_mask);
for_each_set_bit(i, mask, 64) {
if (i >= func->allocated_stack / BPF_REG_SIZE) {
- /* This can happen if backtracking
- * is propagating stack precision where
- * caller has larger stack frame
- * than callee, but backtrack_insn() should
- * have returned -ENOTSUPP.
+ /* the sequence of instructions:
+ * 2: (bf) r3 = r10
+ * 3: (7b) *(u64 *)(r3 -8) = r0
+ * 4: (79) r4 = *(u64 *)(r10 -8)
+ * doesn't contain jmps. It's backtracked
+ * as a single block.
+ * During backtracking insn 3 is not recognized as
+ * stack access, so at the end of backtracking
+ * stack slot fp-8 is still marked in stack_mask.
+ * However the parent state may not have accessed
+ * fp-8 and it's "unallocated" stack space.
+ * In such case fallback to conservative.
*/
- verbose(env, "BUG spi %d stack_size %d\n",
- i, func->allocated_stack);
- WARN_ONCE(1, "verifier backtracking bug");
- return -EFAULT;
+ mark_all_scalars_precise(env, st);
+ return 0;
}
if (func->stack[i].slot_type[0] != STACK_SPILL) {