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selftests/bpf: Add verifier test exercising jit PROBE_MEM logic

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This patch adds a test exercising logic that was fixed / improved in
the previous patch in the series, as well as general sanity checking for
jit's PROBE_MEM logic which should've been unaffected by the previous
patch.

The added verifier test does the following:

  * Acquire a referenced kptr to struct prog_test_ref_kfunc using
    existing net/bpf/test_run.c kfunc
    * Helper returns ptr to a specific prog_test_ref_kfunc whose first
      two fields - both ints - have been prepopulated w/ vals 42 and
      108, respectively
  * kptr_xchg the acquired ptr into an arraymap
  * Do a direct map_value load of the just-added ptr
    * Goal of all this setup is to get an unreferenced kptr pointing to
      struct with ints of known value, which is the result of this step
  * Using unreferenced kptr obtained in previous step, do loads of
    prog_test_ref_kfunc.a (offset 0) and .b (offset 4)
  * Then incr the kptr by 8 and load prog_test_ref_kfunc.a again (this
    time at offset -8)
  * Add all the loaded ints together and return

Before the PROBE_MEM fixes in previous patch, the loads at offset 0 and
4 would succeed, while the load at offset -8 would incorrectly fail
runtime check emitted by the JIT and 0 out dst reg as a result. This
confirmed by retval of 150 for this test before previous patch - since
second .a read is 0'd out - and a retval of 192 with the fixed logic.

The test exercises the two optimizations to fixed logic added in last
patch as well:

  * First load, with insn "r8 = *(u32 *)(r9 + 0)" exercises "insn->off
    is 0, no need to add / sub from src_reg" optimization
  * Third load, with insn "r9 = *(u32 *)(r9 - 8)" exercises "src_reg ==
    dst_reg, no need to restore src_reg after load" optimization

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221216214319.3408356-2-davemarchevsky@fb.com
This commit is contained in:
Dave Marchevsky 2022-12-16 13:43:19 -08:00 committed by Daniel Borkmann
parent 90156f4bfa
commit 59fe41b525
2 changed files with 89 additions and 0 deletions
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28
tools/testing/selftests/bpf/prog_tests/jit_probe_mem.c Normal file
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// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#include <test_progs.h>
#include <network_helpers.h>
#include "jit_probe_mem.skel.h"
void test_jit_probe_mem(void)
{
LIBBPF_OPTS(bpf_test_run_opts, opts,
.data_in = &pkt_v4,
.data_size_in = sizeof(pkt_v4),
.repeat = 1,
);
struct jit_probe_mem *skel;
int ret;
skel = jit_probe_mem__open_and_load();
if (!ASSERT_OK_PTR(skel, "jit_probe_mem__open_and_load"))
return;
ret = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.test_jit_probe_mem), &opts);
ASSERT_OK(ret, "jit_probe_mem ret");
ASSERT_OK(opts.retval, "jit_probe_mem opts.retval");
ASSERT_EQ(skel->data->total_sum, 192, "jit_probe_mem total_sum");
jit_probe_mem__destroy(skel);
}

61
tools/testing/selftests/bpf/progs/jit_probe_mem.c Normal file
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// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#include <vmlinux.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_helpers.h>
static struct prog_test_ref_kfunc __kptr_ref *v;
long total_sum = -1;
extern struct prog_test_ref_kfunc *bpf_kfunc_call_test_acquire(unsigned long *sp) __ksym;
extern void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p) __ksym;
SEC("tc")
int test_jit_probe_mem(struct __sk_buff *ctx)
{
struct prog_test_ref_kfunc *p;
unsigned long zero = 0, sum;
p = bpf_kfunc_call_test_acquire(&zero);
if (!p)
return 1;
p = bpf_kptr_xchg(&v, p);
if (p)
goto release_out;
/* Direct map value access of kptr, should be PTR_UNTRUSTED */
p = v;
if (!p)
return 1;
asm volatile (
"r9 = %[p];"
"%[sum] = 0;"
/* r8 = p->a */
"r8 = *(u32 *)(r9 + 0);"
"%[sum] += r8;"
/* r8 = p->b */
"r8 = *(u32 *)(r9 + 4);"
"%[sum] += r8;"
"r9 += 8;"
/* r9 = p->a */
"r9 = *(u32 *)(r9 - 8);"
"%[sum] += r9;"
: [sum] "=r"(sum)
: [p] "r"(p)
: "r8", "r9"
);
total_sum = sum;
return 0;
release_out:
bpf_kfunc_call_test_release(p);
return 1;
}
char _license[] SEC("license") = "GPL";