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s390/bpf: Support address space cast instruction

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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
This commit is contained in:
Ilya Leoshkevich
2024-07-02 01:40:25 +02:00
committed by Daniel Borkmann
parent 4d3a453b43
commit 555469cc9b
1 changed files with 18 additions and 0 deletions
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18
arch/s390/net/bpf_jit_comp.c
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@@ -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)