Commit cd39d9e6 authored by Haoran Jiang's avatar Haoran Jiang Committed by Huacai Chen
Browse files

LoongArch: BPF: Fix jump offset calculation in tailcall 



The extra pass of bpf_int_jit_compile() skips JIT context initialization
which essentially skips offset calculation leaving out_offset = -1, so
the jmp_offset in emit_bpf_tail_call is calculated by

"#define jmp_offset (out_offset - (cur_offset))"

is a negative number, which is wrong. The final generated assembly are
as follow.

54:	bgeu        	$a2, $t1, -8	    # 0x0000004c
58:	addi.d      	$a6, $s5, -1
5c:	bltz        	$a6, -16	    # 0x0000004c
60:	alsl.d      	$t2, $a2, $a1, 0x3
64:	ld.d        	$t2, $t2, 264
68:	beq         	$t2, $zero, -28	    # 0x0000004c

Before apply this patch, the follow test case will reveal soft lock issues.

cd tools/testing/selftests/bpf/
./test_progs --allow=tailcalls/tailcall_bpf2bpf_1

dmesg:
watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [test_progs:25056]

Cc: stable@vger.kernel.org
Fixes: 5dc61552 ("LoongArch: Add BPF JIT support")
Reviewed-by: default avatarHengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: default avatarHaoran Jiang <jianghaoran@kylinos.cn>
Signed-off-by: default avatarHuacai Chen <chenhuacai@loongson.cn>
parent 6abf17d6

arch/loongarch/net/bpf_jit.c

+5 −16
Original line number Diff line number Diff line
@@ -222,11 +222,9 @@ bool bpf_jit_supports_far_kfunc_call(void) 
	return true;

}



/* initialized on the first pass of build_body() */

static int out_offset = -1;

static int emit_bpf_tail_call(struct jit_ctx *ctx)

static int emit_bpf_tail_call(struct jit_ctx *ctx, int insn)

{

	int off;

	int off, tc_ninsn = 0;

	u8 tcc = tail_call_reg(ctx);

	u8 a1 = LOONGARCH_GPR_A1;

	u8 a2 = LOONGARCH_GPR_A2;
@@ -236,7 +234,7 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx) 
	const int idx0 = ctx->idx;



#define cur_offset (ctx->idx - idx0)

#define jmp_offset (out_offset - (cur_offset))

#define jmp_offset (tc_ninsn - (cur_offset))



	/*

	 * a0: &ctx
@@ -246,6 +244,7 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx) 
	 * if (index >= array->map.max_entries)

	 *	 goto out;

	 */

	tc_ninsn = insn ? ctx->offset[insn+1] - ctx->offset[insn] : ctx->offset[0];

	off = offsetof(struct bpf_array, map.max_entries);

	emit_insn(ctx, ldwu, t1, a1, off);

	/* bgeu $a2, $t1, jmp_offset */
@@ -277,15 +276,6 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx) 
	emit_insn(ctx, ldd, t3, t2, off);

	__build_epilogue(ctx, true);



	/* out: */

	if (out_offset == -1)

		out_offset = cur_offset;

	if (cur_offset != out_offset) {

		pr_err_once("tail_call out_offset = %d, expected %d!\n",

			    cur_offset, out_offset);

		return -1;

	}



	return 0;



toofar:
@@ -930,7 +920,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext 
	/* tail call */

	case BPF_JMP | BPF_TAIL_CALL:

		mark_tail_call(ctx);

		if (emit_bpf_tail_call(ctx) < 0)

		if (emit_bpf_tail_call(ctx, i) < 0)

			return -EINVAL;

		break;
@@ -1855,7 +1845,6 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) 
	if (tmp_blinded)

		bpf_jit_prog_release_other(prog, prog == orig_prog ? tmp : orig_prog);



	out_offset = -1;



	return prog;