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Alexei Starovoitov
2564a031ab
Eduard Zingerman says:
====================
Changes v1 -> v2, suggested by Alexei:
- Resolved conflict with recent commit:
6fcd486b3a ("bpf: Refactor RCU enforcement in the verifier");
- Variable `ctx_access` removed in function `convert_ctx_accesses()`;
- Macro `BPF_COPY_STORE` renamed to `BPF_EMIT_STORE` and fixed to
correctly extract original store instruction class from code.
Original message follows:
The function verifier.c:convert_ctx_access() applies some rewrites to BPF
instructions that read from or write to the BPF program context.
For example, the write instruction for the `struct bpf_sockopt::retval`
field:
*(u32 *)(r1 + offsetof(struct bpf_sockopt, retval)) = r2
Is transformed to:
*(u64 *)(r1 + offsetof(struct bpf_sockopt_kern, tmp_reg)) = r9
r9 = *(u64 *)(r1 + offsetof(struct bpf_sockopt_kern, current_task))
r9 = *(u64 *)(r9 + offsetof(struct task_struct, bpf_ctx))
*(u32 *)(r9 + offsetof(struct bpf_cg_run_ctx, retval)) = r2
r9 = *(u64 *)(r1 + offsetof(struct bpf_sockopt_kern, tmp_reg))
Currently, the verifier only supports such transformations for LDX
(memory-to-register read) and STX (register-to-memory write) instructions.
Error is reported for ST instructions (immediate-to-memory write).
This is fine because clang does not currently emit ST instructions.
However, new `-mcpu=v4` clang flag is planned, which would allow to emit
ST instructions (discussed in [1]).
This patch-set adjusts the verifier to support ST instructions in
`verifier.c:convert_ctx_access()`.
The patches #1 and #2 were previously shared as part of RFC [2]. The
changes compared to that RFC are:
- In patch #1, a bug in the handling of the
`struct __sk_buff::queue_mapping` field was fixed.
- Patch #3 is added, which is a set of disassembler-based test cases for
context access rewrites. The test cases cover all fields for which the
handling code is modified in patch #1.
[1] Propose some new instructions for -mcpu=v4
https://lore.kernel.org/bpf/4bfe98be-5333-1c7e-2f6d-42486c8ec039@meta.com/
[2] RFC Support for BPF_ST instruction in LLVM C compiler
https://lore.kernel.org/bpf/20221231163122.1360813-1-eddyz87@gmail.com/
[3] v1
https://lore.kernel.org/bpf/20230302225507.3413720-1-eddyz87@gmail.com/
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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.