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author | Andrii Nakryiko <andrii@kernel.org> | 2024-04-02 05:13:02 +0300 |
---|---|---|
committer | Alexei Starovoitov <ast@kernel.org> | 2024-04-03 20:29:55 +0300 |
commit | 7bdbf7446305cb65c510c16d57cde82bc76b234a (patch) | |
tree | 76980484fb19439a158181f99fa1f29f553ab189 | |
parent | 2e114248e086fb376405ed3f89b220f8586a2541 (diff) | |
download | linux-7bdbf7446305cb65c510c16d57cde82bc76b234a.tar.xz |
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>
-rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 16 | ||||
-rw-r--r-- | include/linux/filter.h | 20 | ||||
-rw-r--r-- | kernel/bpf/core.c | 5 | ||||
-rw-r--r-- | kernel/bpf/disasm.c | 14 |
4 files changed, 55 insertions, 0 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 3b639d6f2f54..af89dd117dce 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1382,6 +1382,17 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image maybe_emit_mod(&prog, AUX_REG, dst_reg, true); EMIT3(0x0F, 0x44, add_2reg(0xC0, AUX_REG, dst_reg)); break; + } else if (insn_is_mov_percpu_addr(insn)) { + u32 off = (u32)(unsigned long)&this_cpu_off; + + /* mov <dst>, <src> (if necessary) */ + EMIT_mov(dst_reg, src_reg); + + /* add <dst>, gs:[<off>] */ + EMIT2(0x65, add_1mod(0x48, dst_reg)); + EMIT3(0x03, add_1reg(0x04, dst_reg), 0x25); + EMIT(off, 4); + break; } fallthrough; case BPF_ALU | BPF_MOV | BPF_X: @@ -3365,6 +3376,11 @@ bool bpf_jit_supports_subprog_tailcalls(void) return true; } +bool bpf_jit_supports_percpu_insn(void) +{ + return true; +} + void bpf_jit_free(struct bpf_prog *prog) { if (prog->jited) { diff --git a/include/linux/filter.h b/include/linux/filter.h index 531b36090122..161d5f7b64ed 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -178,6 +178,25 @@ struct ctl_table_header; .off = 0, \ .imm = 0 }) +/* 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) + +#define BPF_MOV64_PERCPU_REG(DST, SRC) \ + ((struct bpf_insn) { \ + .code = BPF_ALU64 | BPF_MOV | BPF_X, \ + .dst_reg = DST, \ + .src_reg = SRC, \ + .off = BPF_ADDR_PERCPU, \ + .imm = 0 }) + +static inline bool insn_is_mov_percpu_addr(const struct bpf_insn *insn) +{ + return insn->code == (BPF_ALU64 | BPF_MOV | BPF_X) && insn->off == BPF_ADDR_PERCPU; +} + /* Short form of mov, dst_reg = imm32 */ #define BPF_MOV64_IMM(DST, IMM) \ @@ -972,6 +991,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog); void bpf_jit_compile(struct bpf_prog *prog); bool bpf_jit_needs_zext(void); bool bpf_jit_supports_subprog_tailcalls(void); +bool bpf_jit_supports_percpu_insn(void); bool bpf_jit_supports_kfunc_call(void); bool bpf_jit_supports_far_kfunc_call(void); bool bpf_jit_supports_exceptions(void); 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', |