Commit f6ee298f authored Dec 08, 2022 by Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov Dec 08, 2022

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>

parent 184c9bdb

kernel/bpf/verifier.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -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: