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Dynptr refactorings #4179
Dynptr refactorings #4179
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ARG_PTR_TO_DYNPTR is akin to ARG_PTR_TO_TIMER, ARG_PTR_TO_KPTR, where the underlying register type is subjected to more special checks to determine the type of object represented by the pointer and its state consistency. Move dynptr checks to their own 'process_dynptr_func' function so that is consistent and in-line with existing code. This also makes it easier to reuse this code for kfunc handling. Then, reuse this consolidated function in kfunc dynptr handling too. Note that for kfuncs, the arg_type constraint of DYNPTR_TYPE_LOCAL has been lifted. Acked-by: David Vernet <void@manifault.com> Acked-by: Joanne Koong <joannelkoong@gmail.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Currently, we simply ignore the errors in process_spin_lock, process_timer_func, process_kptr_func, process_dynptr_func. Instead, bubble up the error by storing and checking err variable. Acked-by: Joanne Koong <joannelkoong@gmail.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Recently, user ringbuf support introduced a PTR_TO_DYNPTR register type for use in callback state, because in case of user ringbuf helpers, there is no dynptr on the stack that is passed into the callback. To reflect such a state, a special register type was created. However, some checks have been bypassed incorrectly during the addition of this feature. First, for arg_type with MEM_UNINIT flag which initialize a dynptr, they must be rejected for such register type. Secondly, in the future, there are plans to add dynptr helpers that operate on the dynptr itself and may change its offset and other properties. In all of these cases, PTR_TO_DYNPTR shouldn't be allowed to be passed to such helpers, however the current code simply returns 0. The rejection for helpers that release the dynptr is already handled. For fixing this, we take a step back and rework existing code in a way that will allow fitting in all classes of helpers and have a coherent model for dealing with the variety of use cases in which dynptr is used. First, for ARG_PTR_TO_DYNPTR, it can either be set alone or together with a DYNPTR_TYPE_* constant that denotes the only type it accepts. Next, helpers which initialize a dynptr use MEM_UNINIT to indicate this fact. To make the distinction clear, use MEM_RDONLY flag to indicate that the helper only operates on the memory pointed to by the dynptr, not the dynptr itself. In C parlance, it would be equivalent to taking the dynptr as a point to const argument. When either of these flags are not present, the helper is allowed to mutate both the dynptr itself and also the memory it points to. Currently, the read only status of the memory is not tracked in the dynptr, but it would be trivial to add this support inside dynptr state of the register. With these changes and renaming PTR_TO_DYNPTR to CONST_PTR_TO_DYNPTR to better reflect its usage, it can no longer be passed to helpers that initialize a dynptr, i.e. bpf_dynptr_from_mem, bpf_ringbuf_reserve_dynptr. A note to reviewers is that in code that does mark_stack_slots_dynptr, and unmark_stack_slots_dynptr, we implicitly rely on the fact that PTR_TO_STACK reg is the only case that can reach that code path, as one cannot pass CONST_PTR_TO_DYNPTR to helpers that don't set MEM_RDONLY. In both cases such helpers won't be setting that flag. The next patch will add a couple of selftest cases to make sure this doesn't break. Fixes: 2057156 ("bpf: Add bpf_user_ringbuf_drain() helper") Acked-by: Joanne Koong <joannelkoong@gmail.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
While check_func_arg_reg_off is the place which performs generic checks needed by various candidates of reg->type, there is some handling for special cases, like ARG_PTR_TO_DYNPTR, OBJ_RELEASE, and ARG_PTR_TO_ALLOC_MEM. This commit aims to streamline these special cases and instead leave other things up to argument type specific code to handle. The function will be restrictive by default, and cover all possible cases when OBJ_RELEASE is set, without having to update the function again (and missing to do that being a bug). This is done primarily for two reasons: associating back reg->type to its argument leaves room for the list getting out of sync when a new reg->type is supported by an arg_type. The other case is ARG_PTR_TO_ALLOC_MEM. The problem there is something we already handle, whenever a release argument is expected, it should be passed as the pointer that was received from the acquire function. Hence zero fixed and variable offset. There is nothing special about ARG_PTR_TO_ALLOC_MEM, where technically its target register type PTR_TO_MEM | MEM_ALLOC can already be passed with non-zero offset to other helper functions, which makes sense. Hence, lift the arg_type_is_release check for reg->off and cover all possible register types, instead of duplicating the same kind of check twice for current OBJ_RELEASE arg_types (alloc_mem and ptr_to_btf_id). For the release argument, arg_type_is_dynptr is the special case, where we go to actual object being freed through the dynptr, so the offset of the pointer still needs to allow fixed and variable offset and process_dynptr_func will verify them later for the release argument case as well. This is not specific to ARG_PTR_TO_DYNPTR though, we will need to make this exception for any future object on the stack that needs to be released. In this sense, PTR_TO_STACK as a candidate for object on stack argument is a special case for release offset checks, and they need to be done by the helper releasing the object on stack. Since the check has been lifted above all register type checks, remove the duplicated check that is being done for PTR_TO_BTF_ID. Acked-by: Joanne Koong <joannelkoong@gmail.com> Acked-by: David Vernet <void@manifault.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
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>
It may happen that destination buffer memory overlaps with memory dynptr points to. Hence, we must use memmove to correctly copy from dynptr to destination buffer, or source buffer to dynptr. This actually isn't a problem right now, as memcpy implementation falls back to memmove on detecting overlap and warns about it, but we shouldn't be relying on that. Acked-by: Joanne Koong <joannelkoong@gmail.com> Acked-by: David Vernet <void@manifault.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
The original support for bpf_user_ringbuf_drain callbacks simply short-circuited checks for the dynptr state, allowing users to pass PTR_TO_DYNPTR (now CONST_PTR_TO_DYNPTR) to helpers that initialize a dynptr. This bug would have also surfaced with other dynptr helpers in the future that changed dynptr view or modified it in some way. Include test cases for all cases, i.e. both bpf_dynptr_from_mem and bpf_ringbuf_reserve_dynptr, and ensure verifier rejects both of them. Without the fix, both of these programs load and pass verification. While at it, remove sys_nanosleep target from failure cases' SEC definition, as there is no such tracepoint. Acked-by: David Vernet <void@manifault.com> Acked-by: Joanne Koong <joannelkoong@gmail.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=702716 irrelevant now. Closing PR. |
Pull request for series with
subject: Dynptr refactorings
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=702716