bpf: arm64: remove callee-save registers use for tmp registers

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>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index d0d51903c7e0e40a8ea5668559aa3a583ed33302..49ba37e4bfc0cbdcc0b24175f15513022009c8f6 100644 (file)
--- 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;