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Luis Gerhorst 4ecbcfb71a bpf: Fix verifier_bug_if to account for BPF_CALL 
[ Upstream commit cd3b6a3d49 ]

The BPF verifier assumes `insn_aux->nospec_result` is only set for
direct memory writes (e.g., `*(u32*)(r1+off) = r2`). However, the
assertion fails to account for helper calls (e.g.,
`bpf_skb_load_bytes_relative`) that perform writes to stack memory. Make
the check more precise to resolve this.

The problem is that `BPF_CALL` instructions have `BPF_CLASS(insn->code)
== BPF_JMP`, which triggers the warning check:

- Helpers like `bpf_skb_load_bytes_relative` write to stack memory
- `check_helper_call()` loops through `meta.access_size`, calling
  `check_mem_access(..., BPF_WRITE)`
- `check_stack_write()` sets `insn_aux->nospec_result = 1`
- Since `BPF_CALL` is encoded as `BPF_JMP | BPF_CALL`, the warning fires

Execution flow:

```
1. Drop capabilities → Enable Spectre mitigation
2. Load BPF program
   └─> do_check()
       ├─> check_cond_jmp_op() → Marks dead branch as speculative
       │   └─> push_stack(..., speculative=true)
       ├─> pop_stack() → state->speculative = 1
       ├─> check_helper_call() → Processes helper in dead branch
       │   └─> check_mem_access(..., BPF_WRITE)
       │       └─> insn_aux->nospec_result = 1
       └─> Checks: state->speculative && insn_aux->nospec_result
           └─> BPF_CLASS(insn->code) == BPF_JMP → WARNING
```

To fix the assert, it would be nice to be able to reuse
bpf_insn_successors() here, but bpf_insn_successors()->cnt is not
exactly what we want as it may also be 1 for BPF_JA. Instead, we could
check opcode_info.can_jump, but then we would have to share the table
between the functions. This would mean moving the table out of the
function and adding bpf_opcode_info(). As the verifier_bug_if() only
runs for insns with nospec_result set, the impact on verification time
would likely still be negligible. However, I assume sharing
bpf_opcode_info() between liveness.c and verifier.c will not be worth
it. It seems as only adjust_jmp_off() could also be simplified using it,
and there imm/off is touched. Thus it is maybe better to rely on exact
opcode/class matching there.

Therefore, to avoid this sharing only for a verifier_bug_if(), just
check the opcode. This should now cover all opcodes for which can_jump
in bpf_insn_successors() is true.

Parts of the description and example are taken from the bug report.

Fixes: dadb59104c ("bpf: Fix aux usage after do_check_insn()")
Signed-off-by: Luis Gerhorst <luis.gerhorst@fau.de>
Reported-by: Yinhao Hu <dddddd@hust.edu.cn>
Reported-by: Kaiyan Mei <M202472210@hust.edu.cn>
Reported-by: Dongliang Mu <dzm91@hust.edu.cn>
Closes: https://lore.kernel.org/bpf/7678017d-b760-4053-a2d8-a6879b0dbeeb@hust.edu.cn/
Link: https://lore.kernel.org/r/20260127115912.3026761-2-luis.gerhorst@fau.de
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-02-26 14:59:04 -08:00
arch ARM: VDSO: Patch out __vdso_clock_getres() if unavailable 2026-02-26 14:59:02 -08:00
block block,bfq: fix aux stat accumulation destination 2026-02-11 13:41:47 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:32:12 +01:00
Documentation fou: Don't allow 0 for FOU_ATTR_IPPROTO. 2026-01-30 10:32:12 +01:00
drivers hwrng: airoha - set rng quality to 900 2026-02-26 14:59:04 -08:00
fs iomap: fix submission side handling of completion side errors 2026-02-26 14:59:00 -08:00
include bpf: Fix tcx/netkit detach permissions when prog fd isn't given 2026-02-26 14:59:04 -08:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/kbuf: fix memory leak if io_buffer_add_list fails 2026-02-26 14:59:01 -08:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel bpf: Fix verifier_bug_if to account for BPF_CALL 2026-02-26 14:59:04 -08:00
lib procfs: avoid fetching build ID while holding VMA lock 2026-02-11 13:41:41 +01:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather 2026-02-19 16:31:34 +01:00
net bpf, sockmap: Fix FIONREAD for sockmap 2026-02-26 14:59:04 -08:00
rust rust: driver: fix broken intra-doc links to example driver types 2026-02-19 16:31:31 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:17:11 +01:00
scripts scripts: generate_rust_analyzer: Add compiler_builtins -> core dep 2026-02-06 16:57:42 +01:00
security keys/trusted_keys: fix handle passed to tpm_buf_append_name during unseal 2026-01-30 10:32:22 +01:00
sound ASoC: fsl_xcvr: fix missing lock in fsl_xcvr_mode_put() 2026-02-19 16:31:34 +01:00
tools selftests/bpf: Fix resource leak in serial_test_wq on attach failure 2026-02-26 14:59:03 -08:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:41:44 +01:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.13 2026-02-19 16:31:37 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

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 reStructuredText 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.