bpf: Move PTR_TO_STACK alignment check to process_dynptr_func

After previous commit, we are minimizing helper specific assumptions
from check_func_arg_reg_off, making it generic, and offloading checks
for a specific argument type to their respective functions called after
check_func_arg_reg_off has been called.

This allows relying on a consistent set of guarantees after that call
and then relying on them in code that deals with registers for each
argument type later. This is in line with how process_spin_lock,
process_timer_func, process_kptr_func check reg->var_off to be constant.
The same reasoning is used here to move the alignment check into
process_dynptr_func. Note that it also needs to check for constant
var_off, and accumulate the constant var_off when computing the spi in
get_spi, but that fix will come in later changes.

Acked-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221207204141.308952-6-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8a7e964..9791788 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5932,6 +5932,14 @@ int process_dynptr_func(struct bpf_verifier_env *env, int regno,
                verbose(env, "verifier internal error: misconfigured dynptr helper type flags\n");
                return -EFAULT;
        }
+       /* CONST_PTR_TO_DYNPTR already has fixed and var_off as 0 due to
+        * check_func_arg_reg_off's logic. We only need to check offset
+        * alignment for PTR_TO_STACK.
+        */
+       if (reg->type == PTR_TO_STACK && (reg->off % BPF_REG_SIZE)) {
+               verbose(env, "cannot pass in dynptr at an offset=%d\n", reg->off);
+               return -EINVAL;
+       }
        /*  MEM_UNINIT - Points to memory that is an appropriate candidate for
         *               constructing a mutable bpf_dynptr object.
         *
@@ -6301,11 +6309,6 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
        switch (type) {
        /* Pointer types where both fixed and variable offset is explicitly allowed: */
        case PTR_TO_STACK:
-               if (arg_type_is_dynptr(arg_type) && reg->off % BPF_REG_SIZE) {
-                       verbose(env, "cannot pass in dynptr at an offset\n");
-                       return -EINVAL;
-               }
-               fallthrough;
        case PTR_TO_PACKET:
        case PTR_TO_PACKET_META:
        case PTR_TO_MAP_KEY: