@@ -296,6 +296,49 @@ static void bpf_fill_scale(struct bpf_test *self)
}
}
+static int bpf_fill_torturous_jumps_insn(struct bpf_insn *insn)
+{
+ unsigned int len = 259, hlen = 128;
+ int i;
+
+ insn[0] = BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32);
+ for (i = 1; i <= hlen; i++) {
+ insn[i] = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, i, hlen);
+ insn[i + hlen] = BPF_JMP_A(hlen - i);
+ }
+ insn[len - 2] = BPF_MOV64_IMM(BPF_REG_0, 1);
+ insn[len - 1] = BPF_EXIT_INSN();
+
+ return len;
+}
+
+static void bpf_fill_torturous_jumps(struct bpf_test *self)
+{
+ struct bpf_insn *insn = self->fill_insns;
+ int i = 0;
+
+ switch (self->retval) {
+ case 1:
+ self->prog_len = bpf_fill_torturous_jumps_insn(insn);
+ return;
+ case 2:
+ /* main */
+ insn[i++] = BPF_RAW_INSN(BPF_JMP|BPF_CALL, 0, 1, 0, 3);
+ insn[i++] = BPF_ST_MEM(BPF_B, BPF_REG_10, -32, 0);
+ insn[i++] = BPF_MOV64_IMM(BPF_REG_0, 2);
+ insn[i++] = BPF_EXIT_INSN();
+
+ /* subprog */
+ i += bpf_fill_torturous_jumps_insn(insn + i);
+
+ self->prog_len = i;
+ return;
+ default:
+ self->prog_len = 0;
+ break;
+ }
+}
+
/* BPF_SK_LOOKUP contains 13 instructions, if you need to fix up maps */
#define BPF_SK_LOOKUP(func) \
/* struct bpf_sock_tuple tuple = {} */ \
@@ -105,3 +105,19 @@
.result = ACCEPT,
.retval = 2,
},
+{
+ "jit: torturous jumps",
+ .insns = { },
+ .fill_helper = bpf_fill_torturous_jumps,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ .result = ACCEPT,
+ .retval = 1,
+},
+{
+ "jit: torturous jumps in subprog",
+ .insns = { },
+ .fill_helper = bpf_fill_torturous_jumps,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ .result = ACCEPT,
+ .retval = 2,
+},
There are two tests added into verifier's jit tests to trigger x64 jit jump padding. The first test can be represented as the following assembly code: 1: bpf_call bpf_get_prandom_u32 2: if r0 == 0 goto pc+128 3: if r0 == 1 goto pc+128 ... 129: if r0 == 127 goto pc+128 130: goto pc+128 131: goto pc+127 ... 256: goto pc+1 257: goto pc+0 258: r0 = 1 259: ret We first store a random number to r0 and add the corresponding conditional jumps (2~129) to make verifier believe that those jump instructions from 130 to 257 are reachable. When the program is sent to x64 jit, it starts to optimize out the NOP jumps backwards from 257. Since there are 128 such jumps, the program easily reaches 15 passes and triggers jump padding. Here is the x64 jit code of the first test: 0: 0f 1f 44 00 00 nop DWORD PTR [rax+rax*1+0x0] 5: 66 90 xchg ax,ax 7: 55 push rbp 8: 48 89 e5 mov rbp,rsp b: e8 4c 90 75 e3 call 0xffffffffe375905c 10: 48 83 f8 01 cmp rax,0x1 14: 0f 84 fe 04 00 00 je 0x518 1a: 48 83 f8 02 cmp rax,0x2 1e: 0f 84 f9 04 00 00 je 0x51d ... f6: 48 83 f8 18 cmp rax,0x18 fa: 0f 84 8b 04 00 00 je 0x58b 100: 48 83 f8 19 cmp rax,0x19 104: 0f 84 86 04 00 00 je 0x590 10a: 48 83 f8 1a cmp rax,0x1a 10e: 0f 84 81 04 00 00 je 0x595 ... 500: 0f 84 83 01 00 00 je 0x689 506: 48 81 f8 80 00 00 00 cmp rax,0x80 50d: 0f 84 76 01 00 00 je 0x689 513: e9 71 01 00 00 jmp 0x689 518: e9 6c 01 00 00 jmp 0x689 ... 5fe: e9 86 00 00 00 jmp 0x689 603: e9 81 00 00 00 jmp 0x689 608: 0f 1f 00 nop DWORD PTR [rax] 60b: eb 7c jmp 0x689 60d: eb 7a jmp 0x689 ... 683: eb 04 jmp 0x689 685: eb 02 jmp 0x689 687: 66 90 xchg ax,ax 689: b8 01 00 00 00 mov eax,0x1 68e: c9 leave 68f: c3 ret As expected, a 3 bytes NOPs is inserted at 608 due to the transition from imm32 jmp to imm8 jmp. A 2 bytes NOPs is also inserted at 687 to replace a NOP jump. The second test is to invoke the first test as a subprog to test bpf2bpf. Per the system log, there was one more jit happened with only one pass and the same jit code was produced. Signed-off-by: Gary Lin <glin@suse.com> --- tools/testing/selftests/bpf/test_verifier.c | 43 +++++++++++++++++++++ tools/testing/selftests/bpf/verifier/jit.c | 16 ++++++++ 2 files changed, 59 insertions(+)