[bpf-next,2/2] bpf: Add arm64 JIT support for bpf_addr_space_cast instruction.

Commit Message

Puranjay Mohan March 14, 2024, 3 p.m. UTC

LLVM generates bpf_addr_space_cast instruction while translating
pointers between native (zero) address space and
__attribute__((address_space(N))). The addr_space=1 is reserved as
bpf_arena address space.

rY = addr_space_cast(rX, 0, 1) is processed by the verifier and
converted to normal 32-bit move: wX = wY

rY = addr_space_cast(rX, 1, 0) has to be converted by JIT:

Here I explain using symbolic language what the JIT is supposed to do:
We have:
	src = [src_upper32][src_lower32] // 64 bit src kernel pointer
	uvm = [uvm_upper32][uvm_lower32] // 64 bit user_vm_start

The JIT has to make the dst reg like following
	dst = [uvm_upper32][src_lower32] // if src_lower32 != 0
	dst = [00000000000][00000000000] // if src_lower32 == 0

Signed-off-by: Puranjay Mohan <[e-mail]>
---
 arch/arm64/net/bpf_jit.h                     |  1 +
 arch/arm64/net/bpf_jit_comp.c                | 35 ++++++++++++++++++++
 tools/testing/selftests/bpf/DENYLIST.aarch64 |  2 --
 3 files changed, 36 insertions(+), 2 deletions(-)

Patch

diff --git a/arch/arm64/net/bpf_jit.h b/arch/arm64/net/bpf_jit.h
index 23b1b34db088..813c3c428fde 100644
--- a/arch/arm64/net/bpf_jit.h
+++ b/arch/arm64/net/bpf_jit.h
@@ -238,6 +238,7 @@ 
 #define A64_LSLV(sf, Rd, Rn, Rm) A64_DATA2(sf, Rd, Rn, Rm, LSLV)
 #define A64_LSRV(sf, Rd, Rn, Rm) A64_DATA2(sf, Rd, Rn, Rm, LSRV)
 #define A64_ASRV(sf, Rd, Rn, Rm) A64_DATA2(sf, Rd, Rn, Rm, ASRV)
+#define A64_RORV(sf, Rd, Rn, Rm) A64_DATA2(sf, Rd, Rn, Rm, RORV)
 
 /* Data-processing (3 source) */
 /* Rd = Ra + Rn * Rm */
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index ce66c17b73a0..e12e0df3ad1a 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -82,6 +82,7 @@  struct jit_ctx {
 	__le32 *ro_image;
 	u32 stack_size;
 	int fpb_offset;
+	u64 user_vm_start;
 };
 
 struct bpf_plt {
@@ -868,6 +869,34 @@  static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 	/* dst = src */
 	case BPF_ALU | BPF_MOV | BPF_X:
 	case BPF_ALU64 | BPF_MOV | BPF_X:
+		if (insn->off == BPF_ADDR_SPACE_CAST &&
+		    insn->imm == 1U << 16) {
+			/* Zero out tmp2 */
+			emit(A64_EOR(1, tmp2, tmp2, tmp2), ctx);
+
+			/* Move lo_32_bits(src) to dst */
+			if (dst != src)
+				emit(A64_MOV(0, dst, src), ctx);
+
+			/* Logical shift left by 32 bits */
+			emit(A64_LSL(1, dst, dst, 32), ctx);
+
+			/* Get upper 32 bits of user_vm_start in tmp */
+			emit_a64_mov_i(0, tmp, ctx->user_vm_start >> 32, ctx);
+
+			/* dst |= up_32_bits(user_vm_start) */
+			emit(A64_ORR(1, dst, dst, tmp), ctx);
+
+			/* Rotate by 32 bits to get final result */
+			emit_a64_mov_i(0, tmp, 32, ctx);
+			emit(A64_RORV(1, dst, dst, tmp), ctx);
+
+			/* If lo_32_bits(dst) == 0, set dst = tmp2(0) */
+			emit(A64_CBZ(0, dst, 2), ctx);
+			emit(A64_MOV(1, tmp2, dst), ctx);
+			emit(A64_MOV(1, dst, tmp2), ctx);
+		break;
+		}
 		switch (insn->off) {
 		case 0:
 			emit(A64_MOV(is64, dst, src), ctx);
@@ -1690,6 +1719,7 @@  struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	}
 
 	ctx.fpb_offset = find_fpb_offset(prog);
+	ctx.user_vm_start = bpf_arena_get_user_vm_start(prog->aux->arena);
 
 	/*
 	 * 1. Initial fake pass to compute ctx->idx and ctx->offset.
@@ -2514,6 +2544,11 @@  bool bpf_jit_supports_exceptions(void)
 	return true;
 }
 
+bool bpf_jit_supports_arena(void)
+{
+	return true;
+}
+
 void bpf_jit_free(struct bpf_prog *prog)
 {
 	if (prog->jited) {
diff --git a/tools/testing/selftests/bpf/DENYLIST.aarch64 b/tools/testing/selftests/bpf/DENYLIST.aarch64
index d8ade15e2789..0445ac38bc07 100644
--- a/tools/testing/selftests/bpf/DENYLIST.aarch64
+++ b/tools/testing/selftests/bpf/DENYLIST.aarch64
@@ -10,5 +10,3 @@  fill_link_info/kprobe_multi_link_info            # bpf_program__attach_kprobe_mu
 fill_link_info/kretprobe_multi_link_info         # bpf_program__attach_kprobe_multi_opts unexpected error: -95
 fill_link_info/kprobe_multi_invalid_ubuff        # bpf_program__attach_kprobe_multi_opts unexpected error: -95
 missed/kprobe_recursion                          # missed_kprobe_recursion__attach unexpected error: -95 (errno 95)
-verifier_arena                                   # JIT does not support arena
-arena_htab                                       # JIT does not support arena