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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: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210914091842.4186267-15-johan.almbladh@anyfinetworks.com
This commit is contained in:
Johan Almbladh 2021-09-14 11:18:42 +02:00 committed by Daniel Borkmann
parent 18935a72eb
commit 29eef85be2
1 changed files with 83 additions and 3 deletions
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86
lib/test_bpf.c
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@ -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;
}
}