s390/bpf: Use kernel's expoline thunks

Simplify the JIT code by replacing the custom expolines with the ones
defined in the kernel text.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20250519223646.66382-4-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 70a93e0..c7f8313 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -48,8 +48,6 @@ struct bpf_jit {
        int lit64;              /* Current position in 64-bit literal pool */
        int base_ip;            /* Base address for literal pool */
        int exit_ip;            /* Address of exit */
-       int r1_thunk_ip;        /* Address of expoline thunk for 'br %r1' */
-       int r14_thunk_ip;       /* Address of expoline thunk for 'br %r14' */
        int tail_call_start;    /* Tail call start offset */
        int excnt;              /* Number of exception table entries */
        int prologue_plt_ret;   /* Return address for prologue hotpatch PLT */
@@ -642,28 +640,17 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp,
 }
 
 /*
- * Emit an expoline for a jump that follows
+ * Jump using a register either directly or via an expoline thunk
  */
-static void emit_expoline(struct bpf_jit *jit)
-{
-       /* exrl %r0,.+10 */
-       EMIT6_PCREL_RIL(0xc6000000, jit->prg + 10);
-       /* j . */
-       EMIT4_PCREL(0xa7f40000, 0);
-}
-
-/*
- * Emit __s390_indirect_jump_r1 thunk if necessary
- */
-static void emit_r1_thunk(struct bpf_jit *jit)
-{
-       if (nospec_uses_trampoline()) {
-               jit->r1_thunk_ip = jit->prg;
-               emit_expoline(jit);
-               /* br %r1 */
-               _EMIT2(0x07f1);
-       }
-}
+#define EMIT_JUMP_REG(reg) do {                                                \
+       if (nospec_uses_trampoline())                                   \
+               /* brcl 0xf,__s390_indirect_jump_rN */                  \
+               EMIT6_PCREL_RILC_PTR(0xc0040000, 0x0f,                  \
+                                    __s390_indirect_jump_r ## reg);    \
+       else                                                            \
+               /* br %rN */                                            \
+               _EMIT2(0x07f0 | reg);                                   \
+} while (0)
 
 /*
  * Call r1 either directly or via __s390_indirect_jump_r1 thunk
@@ -672,7 +659,8 @@ static void call_r1(struct bpf_jit *jit)
 {
        if (nospec_uses_trampoline())
                /* brasl %r14,__s390_indirect_jump_r1 */
-               EMIT6_PCREL_RILB(0xc0050000, REG_14, jit->r1_thunk_ip);
+               EMIT6_PCREL_RILB_PTR(0xc0050000, REG_14,
+                                    __s390_indirect_jump_r1);
        else
                /* basr %r14,%r1 */
                EMIT2(0x0d00, REG_14, REG_1);
@@ -688,16 +676,7 @@ static void bpf_jit_epilogue(struct bpf_jit *jit, u32 stack_depth)
        EMIT4(0xb9040000, REG_2, BPF_REG_0);
        /* Restore registers */
        save_restore_regs(jit, REGS_RESTORE, stack_depth, 0);
-       if (nospec_uses_trampoline()) {
-               jit->r14_thunk_ip = jit->prg;
-               /* Generate __s390_indirect_jump_r14 thunk */
-               emit_expoline(jit);
-       }
-       /* br %r14 */
-       _EMIT2(0x07fe);
-
-       if (is_first_pass(jit) || (jit->seen & SEEN_FUNC))
-               emit_r1_thunk(jit);
+       EMIT_JUMP_REG(14);
 
        jit->prg = ALIGN(jit->prg, 8);
        jit->prologue_plt = jit->prg;
@@ -1899,7 +1878,8 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
                        /* aghi %r1,tail_call_start */
                        EMIT4_IMM(0xa70b0000, REG_1, jit->tail_call_start);
                        /* brcl 0xf,__s390_indirect_jump_r1 */
-                       EMIT6_PCREL_RILC(0xc0040000, 0xf, jit->r1_thunk_ip);
+                       EMIT6_PCREL_RILC_PTR(0xc0040000, 0xf,
+                                            __s390_indirect_jump_r1);
                } else {
                        /* bc 0xf,tail_call_start(%r1) */
                        _EMIT4(0x47f01000 + jit->tail_call_start);
@@ -2868,17 +2848,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
               0xf000 | tjit->tccnt_off);
        /* aghi %r15,stack_size */
        EMIT4_IMM(0xa70b0000, REG_15, tjit->stack_size);
-       /* Emit an expoline for the following indirect jump. */
-       if (nospec_uses_trampoline())
-               emit_expoline(jit);
        if (flags & BPF_TRAMP_F_SKIP_FRAME)
-               /* br %r14 */
-               _EMIT2(0x07fe);
+               EMIT_JUMP_REG(14);
        else
-               /* br %r1 */
-               _EMIT2(0x07f1);
-
-       emit_r1_thunk(jit);
+               EMIT_JUMP_REG(1);
 
        return 0;
 }