s390/bpf: Support address space cast instruction

The new address cast instruction translates arena offsets to userspace
addresses. NULL pointers must not be translated.

The common code sets up the mappings in such a way that it's enough to
replace the higher 32 bits to achieve the desired result. s390x has
just an instruction for this: INSERT IMMEDIATE.

Implement the sequence using 3 instruction: LOAD AND TEST, BRANCH
RELATIVE ON CONDITION and INSERT IMMEDIATE.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240701234304.14336-8-iii@linux.ibm.com

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 4b62b5162dfb1a99144e35a608281e22ad8b00a7..39c1d9aa7f1ef631d9d41bdf64a93e027f61791b 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -54,6 +54,7 @@ struct bpf_jit {
        int prologue_plt_ret;   /* Return address for prologue hotpatch PLT */
        int prologue_plt;       /* Start of prologue hotpatch PLT */
        int kern_arena;         /* Pool offset of kernel arena address */
+       u64 user_arena;         /* User arena address */
 };
 
 #define SEEN_MEM       BIT(0)          /* use mem[] for temporary storage */
@@ -863,6 +864,22 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
                }
                break;
        case BPF_ALU64 | BPF_MOV | BPF_X:
+               if (insn_is_cast_user(insn)) {
+                       int patch_brc;
+
+                       /* ltgr %dst,%src */
+                       EMIT4(0xb9020000, dst_reg, src_reg);
+                       /* brc 8,0f */
+                       patch_brc = jit->prg;
+                       EMIT4_PCREL_RIC(0xa7040000, 8, 0);
+                       /* iihf %dst,user_arena>>32 */
+                       EMIT6_IMM(0xc0080000, dst_reg, jit->user_arena >> 32);
+                       /* 0: */
+                       if (jit->prg_buf)
+                               *(u16 *)(jit->prg_buf + patch_brc + 2) =
+                                       (jit->prg - patch_brc) >> 1;
+                       break;
+               }
                switch (insn->off) {
                case 0: /* DST = SRC */
                        /* lgr %dst,%src */
@@ -2076,6 +2093,7 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp,
        kern_arena = bpf_arena_get_kern_vm_start(fp->aux->arena);
        if (kern_arena)
                jit->kern_arena = _EMIT_CONST_U64(kern_arena);
+       jit->user_arena = bpf_arena_get_user_vm_start(fp->aux->arena);
 
        bpf_jit_prologue(jit, fp, stack_depth);
        if (bpf_set_addr(jit, 0) < 0)