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b54a8e130c
Anton Protopopov says:
====================
BPF indirect jumps
This patchset implements a new type of map, instruction set, and uses
it to build support for indirect branches in BPF (on x86). (The same
map will be later used to provide support for indirect calls and static
keys.) See [1], [2] for more context.
Short table of contents:
* Patches 1-6 implement the new map of type
BPF_MAP_TYPE_INSN_SET and corresponding selftests. This map can
be used to track the "original -> xlated -> jitted mapping" for
a given program.
* Patches 7-12 implement the support for indirect jumps on x86 and add libbpf
support for LLVM-compiled programs containing indirect jumps, and selftests.
The jump table support was merged to LLVM and now can be
enabled with -mcpu=v4, see [3]. The __BPF_FEATURE_GOTOX
macros can be used to check if the compiler supports the
feature or not.
See individual patches for more details on the implementation details.
v10 -> v11 (this series):
* rearranged patches and split libbpf patch such that first 6 patches
implementing instruction arrays can be applied independently
* instruction arrays:
* move [fake] aux->used_maps assignment in this patch
* indirect jumps:
* call clear_insn_aux_data before bpf_remove_insns (AI)
* libbpf:
* remove the relocations check after the new LLVM is released (Eduard, Yonghong)
* libbpf: fix an index printed in pr_warn (AI)
* selftests:
* protect programs triggered by nanosleep from fake runs (Eduard)
* patch verifier_gotox to not emit .rel.jumptables
v9 -> v10 (https://lore.kernel.org/bpf/20251102205722.3266908-1-a.s.protopopov@gmail.com/T/#t):
* Three bugs were noticed by AI in v9 (two old, one introduced by v9):
* [new] insn_array_alloc_size could overflow u32, switched to u64 (AI)
* map_ptr should be compared in regsafe for PTR_TO_INSN (AI)
* duplicate elements were copied in jt_from_map (AI)
* added a selftest in verifier_gotox with a jump table containing non-unique entries
v8 -> v9 (https://lore.kernel.org/bpf/20251101110717.2860949-1-a.s.protopopov@gmail.com/T/#t):
* instruction arrays:
* remove the size restriction of 256 elements
* add a comments about addrs usage, old and new (Alexei)
* libbpf:
* properly prefix warnings (Andrii)
* cast j[t] to long long for printf and some other minor cleanups (Andrii)
* selftests:
* use __BPF_FEATURE_GOTOX in selftests and skip tests if it's not set (Eduard)
* fix a typo in a selftest assembly (AI)
v7 -> v8 (https://lore.kernel.org/bpf/20251028142049.1324520-1-a.s.protopopov@gmail.com/T/#u):
* instruction arrays:
* simplify the bpf_prog_update_insn_ptrs function (Eduard)
* remove a semicolon after a function definition (AI)
* libbpf:
* add a proper error path in libbpf patch (AI)
* re-re-factor the create_jt_map & find_subprog_idx (Eduard)
* selftests:
* verifier_gotox: add a test for a jump table pointing to outside of a subprog (Eduard)
* used test__skip instead of just running an empty test
* split tests in bpf_gotox into subtests for convenience
* random:
* drop the docs commit for now
v6 -> v7 (https://lore.kernel.org/bpf/20251026192709.1964787-1-a.s.protopopov@gmail.com/T/#t):
* rebased and dropped already merged commits
* instruction arrays
* use jit_data to find mappings from insn to jit (Alexei)
* alloc `ips` as part of the main allocation (Eduard)
* the `jitted_ip` member wasn't actually used (Eduard)
* remove the bpf_insn_ptr structure, which is not needed for this patch
* indirect jumps, kernel:
* fix a memory leak in `create_jt` (AI)
* use proper reg+8*ereg in `its_static_thunk` (AI)
* some minor cleanups (Eduard)
* indirect jumps, libbpf:
* refactor the `jt_adjust_off()` piece (Edurad)
* move "JUMPTABLES_SEC" into libbpf_internal.h (Eduard)
* remove an unnecessary if (Eduard)
* verifier_gotox: add tests to verify that `gotox rX` works with all registers
v5 -> v6 (https://lore.kernel.org/bpf/20251019202145.3944697-1-a.s.protopopov@gmail.com/T/#u):
* instruction arrays:
* better document `struct bpf_insn_array_value` (Eduard)
* remove a condition in `bpf_insn_array_adjust_after_remove` (Eduard)
* make userspace see original, xlated, and jitted indexes (+original) (Eduard)
* indirect jumps, kernel:
* reject writes to the map
* reject unaligned ops
* add a check what `w` is not outside the program in check_config for `gotox` (Eduard)
* do not introduce unneeded `bpf_find_containing_subprog_idx`
* simplify error processing for `bpf_find_containing_subprog` (Eduard)
* add `insn_state |= DISCOVERED` when it's discovered (Eduard)
* support SUB operations on PTR_TO_INSN (Eduard)
* make `gotox_tmp_buf` a bpf_iarray and use helper to relocate it (Eduard)
* rename fields of `bpf_iarray` to more generic (Eduard)
* re-implement `visit_gotox_insn` in a loop (Eduard)
* some minor cleanups (Eduard)
* libbpf:
* `struct reloc_desc`: add a comment about `union` (Eduard)
* rename parameters of (and one other place in code) `{create,add}_jt_map` to `sym_off` (Eduard)
* `create_jt_map`: check that size/off are 8-byte aligned (Eduard)
* Selftests:
* instruction array selftests:
* only run tests on x86_64
* write a more generic function to test things to reduce code (Eduard)
* errno wasn't used in checks, so don't reset it (Eduard)
* print `i`, `xlated_off` and `map_out[i]` here (Eduard)
* added `verifier_gotox` selftests which do not depend on LLVM:
* disabled `bpf_gotox` tests by default
* other changes:
* remove an extra function in bpf disasm (Eduard)
* some minor cleanups in the insn_successors patch (Eduard)
* update documentation in `Documentation/bpf/linux-notes.html` about jumps, now it is supported :)
v3 -> v4 -> v5 (https://lore.kernel.org/bpf/20250930125111.1269861-1-a.s.protopopov@gmail.com/):
* [v4 -> v5] rebased on top of the last bpf-next/master
* instruction arrays:
* add copyright (Alexei)
* remove mutexes, add frozen back (Alexei)
* setup 1:1 prog-map correspondence using atomic_xchg
* do not copy/paste array_map_get_next_key, add a common helper (Alexei)
* misc minor code cleanups (Alexei)
* indirect jumps, kernel side:
* remove jt_allocated, just check if insn is gotox (Eduard)
* use copy_register_state instead of individual copies (Eduard)
* in push_stack is_speculative should be inherited (Eduard)
* a few cleanups for insn_successors, including omitting error path (Eduard)
* check if reserved fields are used when considering `gotox` instruction (Eduard)
* read size and alignment of read from insn_array should be 8 (Eduard)
* put buffer for sorting in subfun info and realloc to grow as needed (Eduard)
* properly do `jump_point` / `prune_point` from `push_gotox_edge` (Eduard)
* use range_within to check states (Eduard)
* some minor cleanups and fix commit message (Eduard)
* indirect jumps, libbpf side:
* close map_fd in some error paths in create_jt_map (Andrii)
* maps for jump tables are actually not closed at all, fix this (Andrii)
* rename map from `jt` to `.jumptables` (Andrii)
* use `errstr` in an error message (Andrii)
* rephrase error message to look more standard (Andrii)
* misc other minor renames and cleanups (Andrii)
* selftests:
* add the frozen selftest back
* add a selftest for two jumps loading same table
* some other changes:
* rebase and split insn_successor changes into separate patch
* use PTR_ERR_OR_ZERO in the push stack patch (Eduard)
* indirect jumps on x86: properly re-read *pprog (Eduard)
v2 -> v3 (https://lore.kernel.org/bpf/20250918093850.455051-1-a.s.protopopov@gmail.com/):
* fix build failure when CONFIG_BPF_SYSCALL is not set (kbuild-bot)
* reformat bpftool help messages (Quentin)
v1 -> v2 (https://lore.kernel.org/bpf/20250913193922.1910480-1-a.s.protopopov@gmail.com/):
* push_stack changes:
* sanitize_speculative_path should just return int (Eduard)
* return code from sanitize_speculative_path, not EFAULT (Eduard)
* when BPF_COMPLEXITY_LIMIT_JMP_SEQ is reached, return E2BIG (Eduard)
* indirect jumps:
* omit support for .imm=fd in gotox, as we're not using it for now (Eduard)
* struct jt -> struct bpf_iarray (Eduard)
* insn_successors: rewrite the interface to just return a pointer (Eduard)
* remove min_index/max_index, use umin_value/umax_value instead (Alexei, Eduard)
* move emit_indirect_jump args change to the previous patch (Eduard)
* add a comment to map_mem_size() (Eduard)
* use verifier_bug for some error cases in check_indirect_jump (Eduard)
* clear_insn_aux_data: use start,len instead of start,end (Eduard)
* make regs[insn->dst_reg].type = PTR_TO_INSN part of check_mem_access (Eduard)
* constant blinding changes:
* make subprog_start adjustment better readable (Eduard)
* do not set subprog len, it is already set (Eduard)
* libbpf:
* remove check that relocations from .rodata are ok (Anton)
* do not freeze the map, it is not necessary anymore (Anton)
* rename the goto_x -> gotox everywhere (Anton)
* use u64 when parsing LLVM jump tables (Eduard)
* split patch in two due to spaces->tabs change (Eduard)
* split bpftool changes to bpftool patch (Andrii)
* make sym_size it a union with ext_idx (Andrii)
* properly copy/free the jumptables_data section from elf (Andrii)
* a few cosmetic changes around create_jt_map (Andrii)
* fix some comments + rewrite patch description (Andrii)
* inline bpf_prog__append_subprog_offsets (Andrii)
* subprog_sec_offst -> subprog_sec_off (Andrii)
* !strcmp -> strcmp() == 0 (Andrii)
* make some function names more readable (Andrii)
* allocate table of subfunc offsets via libbpf_reallocarray (Andrii)
* selftests:
* squash insn_array* tests together (Anton)
* fixed build warnings (kernel test robot)
RFC -> v1 (https://lore.kernel.org/bpf/20250816180631.952085-1-a.s.protopopov@gmail.com/):
* I've tried to address all the comments provided by Alexei and
Eduard in RFC. Will try to list the most important of them below.
* One big change: move from older LLVM version [5] to newer [4].
Now LLVM generates jump tables as symbols in the new special
section ".jumptables". Another part of this change is that
libbpf now doesn't try to link map load and goto *rX, as
1) this is absolutely not reliable 2) for some use cases this
is impossible (namely, when more than one jump table can be used
in the same gotox instruction).
* Added insn_successors() support (Alexei, Eduard). This includes
getting rid of the ugly bpf_insn_set_iter_xlated_offset()
interface (Eduard).
* Removed hack for the unreachable instruction, as new LLVM thank to
Eduard doesn't generate it.
* Set mem_size for direct map access properly instead of hacking.
Remove off>0 check. (Alexei)
* Do not allocate new memory for min_index/max_index (Alexei, Eduard)
* Information required during check_cfg is now cached to be reused
later (Alexei + general logic for supporting multiple JT per jump)
* Properly compare registers in regsafe (Alexei, Eduard)
* Remove support for JMP32 (Eduard)
* Better checks in adjust_ptr_min_max_vals (Eduard)
* More selftests were added (but still there's room for more) which
directly use gotox (Alexei)
* More checks and verbose messages added
* "unique pointers" are no more in the map
Links:
1. https://lpc.events/event/18/contributions/1941/
2. https://lwn.net/Articles/1017439/
3. https://github.com/llvm/llvm-project/pull/149715
4. https://github.com/llvm/llvm-project/pull/149715#issuecomment-3274833753
6. rfc: https://lore.kernel.org/bpf/20250615085943.3871208-1-a.s.protopopov@gmail.com/
====================
Link: https://patch.msgid.link/20251105090410.1250500-1-a.s.protopopov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Linux kernel
============
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