Commit 29eef85b authored by Johan Almbladh's avatar Johan Almbladh Committed by Daniel Borkmann
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bpf/tests: Add tail call limit test with external function call 



This patch adds a tail call limit test where the program also emits
a BPF_CALL to an external function prior to the tail call. Mainly
testing that JITed programs preserve its internal register state, for
example tail call count, across such external calls.

Signed-off-by: default avatarJohan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210914091842.4186267-15-johan.almbladh@anyfinetworks.com
parent 18935a72

lib/test_bpf.c

+83 −3
Original line number Diff line number Diff line
@@ -12208,6 +12208,30 @@ struct tail_call_test { 
		     offset, TAIL_CALL_MARKER),	       \

	BPF_JMP_IMM(BPF_TAIL_CALL, 0, 0, 0)



/*

 * A test function to be called from a BPF program, clobbering a lot of

 * CPU registers in the process. A JITed BPF program calling this function

 * must save and restore any caller-saved registers it uses for internal

 * state, for example the current tail call count.

 */

BPF_CALL_1(bpf_test_func, u64, arg)

{

	char buf[64];

	long a = 0;

	long b = 1;

	long c = 2;

	long d = 3;

	long e = 4;

	long f = 5;

	long g = 6;

	long h = 7;



	return snprintf(buf, sizeof(buf),

			"%ld %lu %lx %ld %lu %lx %ld %lu %x",

			a, b, c, d, e, f, g, h, (int)arg);

}

#define BPF_FUNC_test_func __BPF_FUNC_MAX_ID



/*

 * Tail call tests. Each test case may call any other test in the table,

 * including itself, specified as a relative index offset from the calling
@@ -12267,6 +12291,28 @@ static struct tail_call_test tail_call_tests[] = { 
		.flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,

		.result = (MAX_TAIL_CALL_CNT + 1 + 1) * MAX_TESTRUNS,

	},

	{

		"Tail call count preserved across function calls",

		.insns = {

			BPF_LDX_MEM(BPF_W, R2, R1, 0),

			BPF_ALU64_IMM(BPF_ADD, R2, 1),

			BPF_STX_MEM(BPF_W, R1, R2, 0),

			BPF_STX_MEM(BPF_DW, R10, R1, -8),

			BPF_CALL_REL(BPF_FUNC_get_numa_node_id),

			BPF_CALL_REL(BPF_FUNC_ktime_get_ns),

			BPF_CALL_REL(BPF_FUNC_ktime_get_boot_ns),

			BPF_CALL_REL(BPF_FUNC_ktime_get_coarse_ns),

			BPF_CALL_REL(BPF_FUNC_jiffies64),

			BPF_CALL_REL(BPF_FUNC_test_func),

			BPF_LDX_MEM(BPF_DW, R1, R10, -8),

			BPF_ALU32_REG(BPF_MOV, R0, R1),

			TAIL_CALL(0),

			BPF_EXIT_INSN(),

		},

		.stack_depth = 8,

		.flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,

		.result = (MAX_TAIL_CALL_CNT + 1 + 1) * MAX_TESTRUNS,

	},

	{

		"Tail call error path, NULL target",

		.insns = {
@@ -12345,17 +12391,19 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs) 
		/* Relocate runtime tail call offsets and addresses */

		for (i = 0; i < len; i++) {

			struct bpf_insn *insn = &fp->insnsi[i];



			if (insn->imm != TAIL_CALL_MARKER)

				continue;

			long addr = 0;



			switch (insn->code) {

			case BPF_LD | BPF_DW | BPF_IMM:

				if (insn->imm != TAIL_CALL_MARKER)

					break;

				insn[0].imm = (u32)(long)progs;

				insn[1].imm = ((u64)(long)progs) >> 32;

				break;



			case BPF_ALU | BPF_MOV | BPF_K:

				if (insn->imm != TAIL_CALL_MARKER)

					break;

				if (insn->off == TAIL_CALL_NULL)

					insn->imm = ntests;

				else if (insn->off == TAIL_CALL_INVALID)
@@ -12363,6 +12411,38 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs) 
				else

					insn->imm = which + insn->off;

				insn->off = 0;

				break;



			case BPF_JMP | BPF_CALL:

				if (insn->src_reg != BPF_PSEUDO_CALL)

					break;

				switch (insn->imm) {

				case BPF_FUNC_get_numa_node_id:

					addr = (long)&numa_node_id;

					break;

				case BPF_FUNC_ktime_get_ns:

					addr = (long)&ktime_get_ns;

					break;

				case BPF_FUNC_ktime_get_boot_ns:

					addr = (long)&ktime_get_boot_fast_ns;

					break;

				case BPF_FUNC_ktime_get_coarse_ns:

					addr = (long)&ktime_get_coarse_ns;

					break;

				case BPF_FUNC_jiffies64:

					addr = (long)&get_jiffies_64;

					break;

				case BPF_FUNC_test_func:

					addr = (long)&bpf_test_func;

					break;

				default:

					err = -EFAULT;

					goto out_err;

				}

				*insn = BPF_EMIT_CALL(BPF_CAST_CALL(addr));

				if ((long)__bpf_call_base + insn->imm != addr)

					*insn = BPF_JMP_A(0); /* Skip: NOP */

				break;

			}

		}