In the current implementation of ARM64 eBPF JIT, R23 and R24 are used for tmp registers, which are callee-saved registers. This leads to variable size of JIT prologue and epilogue. The latest blinding constant change prefers to constant size of prologue and epilogue. AAPCS reserves R9 ~ R15 for temp registers which not need to be saved/restored during function call. So, replace R23 and R24 to R10 and R11, and remove tmp_used flag to save 2 instructions for some jited BPF program.

CC: Daniel Borkmann daniel@iogearbox.net Acked-by: Zi Shen Lim zlim.lnx@gmail.com Signed-off-by: Yang Shi yang.shi@linaro.org --- Changelog v1 --> v2: * Updated stack diagram * Added the comment from Zi for the commit log * Added Zi's Acked-by

Apply on top of Daniel's blinding constant patchset

arch/arm64/net/bpf_jit_comp.c | 34 +++++----------------------------- 1 file changed, 5 insertions(+), 29 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index d0d5190..49ba37e 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -51,9 +51,9 @@ static const int bpf2a64[] = { [BPF_REG_9] = A64_R(22), /* read-only frame pointer to access stack */ [BPF_REG_FP] = A64_R(25), - /* temporary register for internal BPF JIT */ - [TMP_REG_1] = A64_R(23), - [TMP_REG_2] = A64_R(24), + /* temporary registers for internal BPF JIT */ + [TMP_REG_1] = A64_R(10), + [TMP_REG_2] = A64_R(11), /* temporary register for blinding constants */ [BPF_REG_AX] = A64_R(9), }; @@ -61,7 +61,6 @@ static const int bpf2a64[] = { struct jit_ctx { const struct bpf_prog *prog; int idx; - int tmp_used; int epilogue_offset; int *offset; u32 *image; @@ -154,8 +153,6 @@ static void build_prologue(struct jit_ctx *ctx) const u8 r8 = bpf2a64[BPF_REG_8]; const u8 r9 = bpf2a64[BPF_REG_9]; const u8 fp = bpf2a64[BPF_REG_FP]; - const u8 tmp1 = bpf2a64[TMP_REG_1]; - const u8 tmp2 = bpf2a64[TMP_REG_2];

/* * BPF prog stack layout @@ -167,7 +164,7 @@ static void build_prologue(struct jit_ctx *ctx) * | ... | callee saved registers * +-----+ * | | x25/x26 - * BPF fp register => -80:+-----+ <= (BPF_FP) + * BPF fp register => -64:+-----+ <= (BPF_FP) * | | * | ... | BPF prog stack * | | @@ -189,8 +186,6 @@ static void build_prologue(struct jit_ctx *ctx) /* Save callee-saved register */ emit(A64_PUSH(r6, r7, A64_SP), ctx); emit(A64_PUSH(r8, r9, A64_SP), ctx); - if (ctx->tmp_used) - emit(A64_PUSH(tmp1, tmp2, A64_SP), ctx);

/* Save fp (x25) and x26. SP requires 16 bytes alignment */ emit(A64_PUSH(fp, A64_R(26), A64_SP), ctx); @@ -210,8 +205,6 @@ static void build_epilogue(struct jit_ctx *ctx) const u8 r8 = bpf2a64[BPF_REG_8]; const u8 r9 = bpf2a64[BPF_REG_9]; const u8 fp = bpf2a64[BPF_REG_FP]; - const u8 tmp1 = bpf2a64[TMP_REG_1]; - const u8 tmp2 = bpf2a64[TMP_REG_2];

/* We're done with BPF stack */ emit(A64_ADD_I(1, A64_SP, A64_SP, STACK_SIZE), ctx); @@ -220,8 +213,6 @@ static void build_epilogue(struct jit_ctx *ctx) emit(A64_POP(fp, A64_R(26), A64_SP), ctx);

/* Restore callee-saved register */ - if (ctx->tmp_used) - emit(A64_POP(tmp1, tmp2, A64_SP), ctx); emit(A64_POP(r8, r9, A64_SP), ctx); emit(A64_POP(r6, r7, A64_SP), ctx);

@@ -317,7 +308,6 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx) emit(A64_UDIV(is64, dst, dst, src), ctx); break; case BPF_MOD: - ctx->tmp_used = 1; emit(A64_UDIV(is64, tmp, dst, src), ctx); emit(A64_MUL(is64, tmp, tmp, src), ctx); emit(A64_SUB(is64, dst, dst, tmp), ctx); @@ -390,49 +380,41 @@ emit_bswap_uxt: /* dst = dst OP imm */ case BPF_ALU | BPF_ADD | BPF_K: case BPF_ALU64 | BPF_ADD | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_ADD(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_SUB | BPF_K: case BPF_ALU64 | BPF_SUB | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_SUB(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_AND | BPF_K: case BPF_ALU64 | BPF_AND | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_AND(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_OR | BPF_K: case BPF_ALU64 | BPF_OR | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_ORR(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_XOR | BPF_K: case BPF_ALU64 | BPF_XOR | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_EOR(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_MUL | BPF_K: case BPF_ALU64 | BPF_MUL | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_MUL(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_DIV | BPF_K: case BPF_ALU64 | BPF_DIV | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp, imm, ctx); emit(A64_UDIV(is64, dst, dst, tmp), ctx); break; case BPF_ALU | BPF_MOD | BPF_K: case BPF_ALU64 | BPF_MOD | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(is64, tmp2, imm, ctx); emit(A64_UDIV(is64, tmp, dst, tmp2), ctx); emit(A64_MUL(is64, tmp, tmp, tmp2), ctx); @@ -503,12 +485,10 @@ emit_cond_jmp: case BPF_JMP | BPF_JNE | BPF_K: case BPF_JMP | BPF_JSGT | BPF_K: case BPF_JMP | BPF_JSGE | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(1, tmp, imm, ctx); emit(A64_CMP(1, dst, tmp), ctx); goto emit_cond_jmp; case BPF_JMP | BPF_JSET | BPF_K: - ctx->tmp_used = 1; emit_a64_mov_i(1, tmp, imm, ctx); emit(A64_TST(1, dst, tmp), ctx); goto emit_cond_jmp; @@ -518,7 +498,6 @@ emit_cond_jmp: const u8 r0 = bpf2a64[BPF_REG_0]; const u64 func = (u64)__bpf_call_base + imm;

- ctx->tmp_used = 1; emit_a64_mov_i64(tmp, func, ctx); emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); emit(A64_MOV(1, A64_FP, A64_SP), ctx); @@ -564,7 +543,6 @@ emit_cond_jmp: case BPF_LDX | BPF_MEM | BPF_H: case BPF_LDX | BPF_MEM | BPF_B: case BPF_LDX | BPF_MEM | BPF_DW: - ctx->tmp_used = 1; emit_a64_mov_i(1, tmp, off, ctx); switch (BPF_SIZE(code)) { case BPF_W: @@ -588,7 +566,6 @@ emit_cond_jmp: case BPF_ST | BPF_MEM | BPF_B: case BPF_ST | BPF_MEM | BPF_DW: /* Load imm to a register then store it */ - ctx->tmp_used = 1; emit_a64_mov_i(1, tmp2, off, ctx); emit_a64_mov_i(1, tmp, imm, ctx); switch (BPF_SIZE(code)) { @@ -612,7 +589,6 @@ emit_cond_jmp: case BPF_STX | BPF_MEM | BPF_H: case BPF_STX | BPF_MEM | BPF_B: case BPF_STX | BPF_MEM | BPF_DW: - ctx->tmp_used = 1; emit_a64_mov_i(1, tmp, off, ctx); switch (BPF_SIZE(code)) { case BPF_W: @@ -798,7 +774,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)

/* 1. Initial fake pass to compute ctx->idx. */

- /* Fake pass to fill in ctx->offset and ctx->tmp_used. */ + /* Fake pass to fill in ctx->offset. */ if (build_body(&ctx)) { prog = orig_prog; goto out_off;