diff options
| author | Andrii Nakryiko <andrii@kernel.org> | 2024-04-01 19:13:02 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2024-04-03 10:29:55 -0700 |
| commit | 7bdbf7446305cb65c510c16d57cde82bc76b234a (patch) | |
| tree | 76980484fb19439a158181f99fa1f29f553ab189 /kernel/bpf | |
| parent | 2e114248e086fb376405ed3f89b220f8586a2541 (diff) | |
bpf: add special internal-only MOV instruction to resolve per-CPU addrs
Add a new BPF instruction for resolving absolute addresses of per-CPU
data from their per-CPU offsets. This instruction is internal-only and
users are not allowed to use them directly. They will only be used for
internal inlining optimizations for now between BPF verifier and BPF JITs.
We use a special BPF_MOV | BPF_ALU64 | BPF_X form with insn->off field
set to BPF_ADDR_PERCPU = -1. I used negative offset value to distinguish
them from positive ones used by user-exposed instructions.
Such instruction performs a resolution of a per-CPU offset stored in
a register to a valid kernel address which can be dereferenced. It is
useful in any use case where absolute address of a per-CPU data has to
be resolved (e.g., in inlining bpf_map_lookup_elem()).
BPF disassembler is also taught to recognize them to support dumping
final BPF assembly code (non-JIT'ed version).
Add arch-specific way for BPF JITs to mark support for this instructions.
This patch also adds support for these instructions in x86-64 BPF JIT.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20240402021307.1012571-2-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/core.c | 5 | ||||
| -rw-r--r-- | kernel/bpf/disasm.c | 14 |
2 files changed, 19 insertions, 0 deletions
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index ae406a2814db..7a33a3a7e63c 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2945,6 +2945,11 @@ bool __weak bpf_jit_supports_subprog_tailcalls(void) return false; } +bool __weak bpf_jit_supports_percpu_insn(void) +{ + return false; +} + bool __weak bpf_jit_supports_kfunc_call(void) { return false; diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c index bd2e2dd04740..309c4aa1b026 100644 --- a/kernel/bpf/disasm.c +++ b/kernel/bpf/disasm.c @@ -172,6 +172,17 @@ static bool is_addr_space_cast(const struct bpf_insn *insn) insn->off == BPF_ADDR_SPACE_CAST; } +/* Special (internal-only) form of mov, used to resolve per-CPU addrs: + * dst_reg = src_reg + <percpu_base_off> + * BPF_ADDR_PERCPU is used as a special insn->off value. + */ +#define BPF_ADDR_PERCPU (-1) + +static inline bool is_mov_percpu_addr(const struct bpf_insn *insn) +{ + return insn->code == (BPF_ALU64 | BPF_MOV | BPF_X) && insn->off == BPF_ADDR_PERCPU; +} + void print_bpf_insn(const struct bpf_insn_cbs *cbs, const struct bpf_insn *insn, bool allow_ptr_leaks) @@ -194,6 +205,9 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs, verbose(cbs->private_data, "(%02x) r%d = addr_space_cast(r%d, %d, %d)\n", insn->code, insn->dst_reg, insn->src_reg, ((u32)insn->imm) >> 16, (u16)insn->imm); + } else if (is_mov_percpu_addr(insn)) { + verbose(cbs->private_data, "(%02x) r%d = &(void __percpu *)(r%d)\n", + insn->code, insn->dst_reg, insn->src_reg); } else if (BPF_SRC(insn->code) == BPF_X) { verbose(cbs->private_data, "(%02x) %c%d %s %s%c%d\n", insn->code, class == BPF_ALU ? 'w' : 'r', |