Commit 7f332f9f authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Alexei Starovoitov
Browse files

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: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20250519223646.66382-4-iii@linux.ibm.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 9053ba04

arch/s390/net/bpf_jit_comp.c

+17 −44
Original line number Diff line number Diff line
@@ -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;

}