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Joanne Koong says: ==================== This patchset implements the basics of dynamic pointers in bpf. A dynamic pointer (struct bpf_dynptr) is a pointer that stores extra metadata alongside the address it points to. This abstraction is useful in bpf given that every memory access in a bpf program must be safe. The verifier and bpf helper functions can use the metadata to enforce safety guarantees for things such as dynamically sized strings and kernel heap allocations. From the program side, the bpf_dynptr is an opaque struct and the verifier will enforce that its contents are never written to by the program. It can only be written to through specific bpf helper functions. There are several uses cases for dynamic pointers in bpf programs. Some examples include: dynamically sized ringbuf reservations without extra memcpys, dynamic string parsing and memory comparisons, dynamic memory allocations that can be persisted in maps, and dynamic + ergonomic parsing of sk_buff and xdp_md packet data. At a high-level, the patches are as follows: 1/6 - Adds verifier support for dynptrs 2/6 - Adds bpf_dynptr_from_mem (local dynptr) 3/6 - Adds dynptr support for ring buffers 4/6 - Adds bpf_dynptr_read and bpf_dynptr_write 5/6 - Adds dynptr data slices (ptr to the dynptr data) 6/6 - Tests to check that the verifier rejects invalid cases and passes valid ones This is the first dynptr patchset in a larger series. The next series of patches will add dynptrs that support dynamic memory allocations that can also be persisted in maps, support for parsing packet data through dynptrs, convenience helpers for using dynptrs as iterators, and more helper functions for interacting with strings and memory dynamically. Changelog: ---------- v5 -> v6: v5: https://lore.kernel.org/bpf/20220520044245.3305025-1-joannelkoong@gmail.com/ * enforce PTR_TO_MAP_VALUE for bpf_dynptr_from_mem data in check_helper_call instead of using DYNPTR_TYPE_LOCAL when checking func arg compatiblity * remove MEM_DYNPTR modifier v4 -> v5: v4: https://lore.kernel.org/bpf/20220509224257.3222614-1-joannelkoong@gmail.com/ * Remove malloc dynptr; this will be part of the 2nd patchset while we figure out memory accounting * For data slices, only set the register's ref_obj_id to dynptr_id (Alexei) * Tidying (eg remove "inline", move offset checking to "check_func_arg_reg_off") (David) * Add a few new test cases, remove malloc-only ones. v3 -> v4: v3: https://lore.kernel.org/bpf/20220428211059.4065379-1-joannelkoong@gmail.com/ 1/6 - Change mem ptr + size check to use more concise inequality expression (David + Andrii) 2/6 - Add check for meta->uninit_dynptr_regno not already set (Andrii) Move DYNPTR_TYPE_FLAG_MASK to include/linux/bpf.h (Andrii) 3/6 - Remove four underscores for invoking BPF_CALL (Andrii) Add __BPF_TYPE_FLAG_MAX and use it for __BPF_TYPE_LAST_FLAG (Andrii) 4/6 - Fix capacity to be bpf_dynptr size value in check_off_len (Andrii) Change -EINVAL to -E2BIG if len + offset is out of bounds (Andrii) 5/6 - Add check for only 1 dynptr arg for dynptr data function (Andrii) 6/6 - For ringbuf map, set max_entries from userspace (Andrii) Use err ?: ... for interactring with dynptr APIs (Andrii) Define array_map2 for add_dynptr_to_map2 test where value is a struct with an embedded dynptr Remove ref id from missing_put_callback message, since on different environments, ref id is not always = 1 v2 -> v3: v2: https://lore.kernel.org/bpf/20220416063429.3314021-1-joannelkoong@gmail.com/ * Reorder patches (move ringbuffer patch to be right after the verifier + * malloc dynptr patchset) * Remove local type dynptrs (Andrii + Alexei) * Mark stack slot as STACK_MISC after any writes into a dynptr instead of * explicitly prohibiting writes (Alexei) * Pass number of slots, not memory size to is_spi_bounds_valid (Kumar) * Check reference leaks by adding dynptr id to state->refs instead of checking stack slots (Alexei) v1 -> v2: v1: https://lore.kernel.org/bpf/20220402015826.3941317-1-joannekoong@fb.com/ 1/7 - * Remove ARG_PTR_TO_MAP_VALUE_UNINIT alias and use ARG_PTR_TO_MAP_VALUE | MEM_UNINIT directly (Andrii) * Drop arg_type_is_mem_ptr() wrapper function (Andrii) 2/7 - * Change name from MEM_RELEASE to OBJ_RELEASE (Andrii) * Use meta.release_ref instead of ref_obj_id != 0 to determine whether to release reference (Kumar) * Drop type_is_release_mem() wrapper function (Andrii) 3/7 - * Add checks for nested dynptrs edge-cases, which could lead to corrupt * writes of the dynptr stack variable. * Add u64 flags to bpf_dynptr_from_mem() and bpf_dynptr_alloc() (Andrii) * Rename from bpf_malloc/bpf_free to bpf_dynptr_alloc/bpf_dynptr_put (Alexei) * Support alloc flag __GFP_ZERO (Andrii) * Reserve upper 8 bits in dynptr size and offset fields instead of reserving just the upper 4 bits (Andrii) * Allow dynptr zero-slices (Andrii) * Use the highest bit for is_rdonly instead of the 28th bit (Andrii) * Rename check_* functions to is_* functions for better readability (Andrii) * Add comment for code that checks the spi bounds (Andrii) 4/7 - * Fix doc description for bpf_dynpt_read (Toke) * Move bpf_dynptr_check_off_len() from function patch 1 to here (Andrii) 5/7 - * When finding the id for the dynptr to associate the data slice with, look for dynptr arg instead of assuming it is BPF_REG_1. 6/7 - * Add __force when casting from unsigned long to void * (kernel test * robot) * Expand on docs for ringbuf dynptr APIs (Andrii) 7/7 - * Use table approach for defining test programs and error messages * (Andrii) * Print out full log if there’s an error (Andrii) * Use bpf_object__find_program_by_name() instead of specifying program name as a string (Andrii) * Add 6 extra cases: invalid_nested_dynptrs1, invalid_nested_dynptrs2, invalid_ref_mem1, invalid_ref_mem2, zero_slice_access, and test_alloc_zero_bytes * Add checking for edge cases (eg allocing with invalid flags) ==================== Signed-off-by: Andrii Nakryiko <andrii@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.