On 3/21/2024 11:31 PM, Puranjay Mohan wrote:
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 <puranjay12@xxxxxxxxx>
---
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(-)
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 b9b5febe64f0..37c94ebd06b2 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:
is it legal to encode BPF_ADDR_SPACE_CAST with BPF_ALU?
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);
seems we could simplify it to:
emit_a64_mov_i(0, dst, ctx->user_vm_start >> 32, ctx);
emit(A64_LSL(1, dst, dst, 32), ctx);
emit(A64_MOV(0, tmp, src), ctx); // 32-bit mov clears the upper 32 bits
emit(A64_CBZ(1, tmp, 2), ctx);
emit(A64_ORR(1, tmp, dst, tmp), ctx);
emit(A64_MOV(1, dst, tmp), ctx);
+ break;
not aligned
+ }
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.
@@ -2511,6 +2541,11 @@ 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
