[bpf-next,v2,2/2] selftests/bpf: Add a selftest for x86 jit convergence issues

Commit Message

Yonghong Song Sept. 3, 2024, 10:59 p.m. UTC

The core part of the selftest, i.e., the je <-> jmp cycle, mimics the
original sched-ext bpf program. The test will fail without the
previous patch.

I tried to create some cases for other potential cycles
(je <-> je, jmp <-> je and jmp <-> jmp) with similar pattern
to the test in this patch, but failed. So this patch
only contains one test for je <-> jmp cycle.

Signed-off-by: Yonghong Song <[e-mail]>
---
 .../selftests/bpf/prog_tests/verifier.c       |   2 +
 .../bpf/progs/verifier_jit_convergence.c      | 128 ++++++++++++++++++
 2 files changed, 130 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_jit_convergence.c

Comments

Alexei Starovoitov Sept. 4, 2024, 4:58 p.m. UTC | #1

On Tue, Sep 3, 2024 at 4:00 PM Yonghong Song <[e-mail]> wrote:
>
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_misc.h"
> +
> +#if defined(__TARGET_ARCH_x86)

Does our test framework need this ifdef and dummy_test below?
There is __arch_x86_64 below.
Isn't it enough?

> +SEC("socket")
> +__description("bpf_jit_convergence je <-> jmp")
> +__success __retval(0)
> +__arch_x86_64

Yonghong Song Sept. 4, 2024, 6:28 p.m. UTC | #2

On 9/4/24 9:58 AM, Alexei Starovoitov wrote:
> On Tue, Sep 3, 2024 at 4:00 PM Yonghong Song <[e-mail]> wrote:
>> +#include <linux/bpf.h>
>> +#include <bpf/bpf_helpers.h>
>> +#include "bpf_misc.h"
>> +
>> +#if defined(__TARGET_ARCH_x86)
> Does our test framework need this ifdef and dummy_test below?
> There is __arch_x86_64 below.
> Isn't it enough?

It should be enough. Other arch should be correct although
they do not have convergence issue.

Let me remove above "#if defined(__TARGET_ARCH_x86)" and
do a test again to ensure everything is okay.

>
>> +SEC("socket")
>> +__description("bpf_jit_convergence je <-> jmp")
>> +__success __retval(0)
>> +__arch_x86_64

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 80a90c627182..df398e714dff 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -39,6 +39,7 @@ 
 #include "verifier_int_ptr.skel.h"
 #include "verifier_iterating_callbacks.skel.h"
 #include "verifier_jeq_infer_not_null.skel.h"
+#include "verifier_jit_convergence.skel.h"
 #include "verifier_ld_ind.skel.h"
 #include "verifier_ldsx.skel.h"
 #include "verifier_leak_ptr.skel.h"
@@ -163,6 +164,7 @@  void test_verifier_helper_value_access(void)  { RUN(verifier_helper_value_access
 void test_verifier_int_ptr(void)              { RUN(verifier_int_ptr); }
 void test_verifier_iterating_callbacks(void)  { RUN(verifier_iterating_callbacks); }
 void test_verifier_jeq_infer_not_null(void)   { RUN(verifier_jeq_infer_not_null); }
+void test_verifier_jit_convergence(void)      { RUN(verifier_jit_convergence); }
 void test_verifier_ld_ind(void)               { RUN(verifier_ld_ind); }
 void test_verifier_ldsx(void)                  { RUN(verifier_ldsx); }
 void test_verifier_leak_ptr(void)             { RUN(verifier_leak_ptr); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_jit_convergence.c b/tools/testing/selftests/bpf/progs/verifier_jit_convergence.c
new file mode 100644
index 000000000000..fdc4ccc83c7d
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_jit_convergence.c
@@ -0,0 +1,128 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+#if defined(__TARGET_ARCH_x86)
+
+struct value_t {
+	long long a[32];
+};
+
+struct {
+        __uint(type, BPF_MAP_TYPE_HASH);
+        __uint(max_entries, 1);
+        __type(key, long long);
+        __type(value, struct value_t);
+} map_hash SEC(".maps");
+
+SEC("socket")
+__description("bpf_jit_convergence je <-> jmp")
+__success __retval(0)
+__arch_x86_64
+__jited("	pushq	%rbp")
+__naked void btf_jit_convergence_je_jmp(void)
+{
+	asm volatile (
+	"call %[bpf_get_prandom_u32];"
+	"if r0 == 0 goto l20_%=;"
+	"if r0 == 1 goto l21_%=;"
+	"if r0 == 2 goto l22_%=;"
+	"if r0 == 3 goto l23_%=;"
+	"if r0 == 4 goto l24_%=;"
+	"call %[bpf_get_prandom_u32];"
+	"call %[bpf_get_prandom_u32];"
+"l20_%=:"
+"l21_%=:"
+"l22_%=:"
+"l23_%=:"
+"l24_%=:"
+	"r1 = 0;"
+	"*(u64 *)(r10 - 8) = r1;"
+	"r2 = r10;"
+	"r2 += -8;"
+	"r1 = %[map_hash] ll;"
+	"call %[bpf_map_lookup_elem];"
+	"if r0 == 0 goto l1_%=;"
+	"r6 = r0;"
+	"call %[bpf_get_prandom_u32];"
+	"r7 = r0;"
+	"r5 = r6;"
+	"if r0 != 0x0 goto l12_%=;"
+	"call %[bpf_get_prandom_u32];"
+	"r1 = r0;"
+	"r2 = r6;"
+	"if r1 == 0x0 goto l0_%=;"
+"l9_%=:"
+	"r2 = *(u64 *)(r6 + 0x0);"
+	"r2 += 0x1;"
+	"*(u64 *)(r6 + 0x0) = r2;"
+	"goto l1_%=;"
+"l12_%=:"
+	"r1 = r7;"
+	"r1 += 0x98;"
+	"r2 = r5;"
+	"r2 += 0x90;"
+	"r2 = *(u32 *)(r2 + 0x0);"
+	"r3 = r7;"
+	"r3 &= 0x1;"
+	"r2 *= 0xa8;"
+	"if r3 == 0x0 goto l2_%=;"
+	"r1 += r2;"
+	"r1 -= r7;"
+	"r1 += 0x8;"
+	"if r1 <= 0xb20 goto l3_%=;"
+	"r1 = 0x0;"
+	"goto l4_%=;"
+"l3_%=:"
+	"r1 += r7;"
+"l4_%=:"
+	"if r1 == 0x0 goto l8_%=;"
+	"goto l9_%=;"
+"l2_%=:"
+	"r1 += r2;"
+	"r1 -= r7;"
+	"r1 += 0x10;"
+	"if r1 <= 0xb20 goto l6_%=;"
+	"r1 = 0x0;"
+	"goto l7_%=;"
+"l6_%=:"
+	"r1 += r7;"
+"l7_%=:"
+	"if r1 == 0x0 goto l8_%=;"
+	"goto l9_%=;"
+"l0_%=:"
+	"r1 = 0x3;"
+	"*(u64 *)(r10 - 0x10) = r1;"
+	"r2 = r1;"
+	"goto l1_%=;"
+"l8_%=:"
+	"r1 = r5;"
+	"r1 += 0x4;"
+	"r1 = *(u32 *)(r1 + 0x0);"
+	"*(u64 *)(r10 - 0x8) = r1;"
+"l1_%=:"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_get_prandom_u32),
+	  __imm(bpf_map_lookup_elem),
+	  __imm_addr(map_hash)
+	: __clobber_all);
+}
+
+#else
+
+SEC("socket")
+__description("non-x86 has no jit convergence issue, use a dummy test")
+__success
+int dummy_test(void)
+{
+	return 0;
+}
+
+#endif
+
+char _license[] SEC("license") = "GPL";