From: Gary Lin glin@suse.com
mainline inclusion from mainline-5.12-rc1 commit 79d1b684e21533bd417df50704a9692830eb8358 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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There are 3 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 == 1 goto pc+128 3: if r0 == 2 goto pc+128 ... 129: if r0 == 128 goto pc+128 130: goto pc+128 131: goto pc+127 ... 256: goto pc+2 257: goto pc+1 258: 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 case is tricky. Here is the assembly code:
1: bpf_call bpf_get_prandom_u32 2: if r0 == 1 goto pc+2048 3: if r0 == 2 goto pc+2048 ... 2049: if r0 == 2048 goto pc+2048 2050: goto pc+2048 2051: goto pc+16 2052: goto pc+15 ... 2064: goto pc+3 2065: goto pc+2 2066: goto pc+1 ... [repeat "goto pc+16".."goto pc+1" 127 times] ... 4099: r0 = 2 4100: ret
There are 4 major parts of the program. 1) 1~2049: Those are instructions to make 2050~4098 reachable. Some of them also could generate the padding for jmp_cond. 2) 2050: This is the target instruction for the imm32 nop jmp padding. 3) 2051~4098: The repeated "goto 1~16" instructions are designed to be consumed by the nop jmp optimization. In the end, those instrucitons become 128 continuous 0 offset jmp and are optimized out in 1 pass, and this make insn 2050 an imm32 nop jmp in the next pass, so that we can trigger the 5 bytes padding. 4) 4099~4100: Those are the instructions to end the program.
The x64 jit code is like this:
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 bc 7b d5 d3 call 0xffffffffd3d57bcc 10: 48 83 f8 01 cmp rax,0x1 14: 0f 84 7e 66 00 00 je 0x6698 1a: 48 83 f8 02 cmp rax,0x2 1e: 0f 84 74 66 00 00 je 0x6698 24: 48 83 f8 03 cmp rax,0x3 28: 0f 84 6a 66 00 00 je 0x6698 2e: 48 83 f8 04 cmp rax,0x4 32: 0f 84 60 66 00 00 je 0x6698 38: 48 83 f8 05 cmp rax,0x5 3c: 0f 84 56 66 00 00 je 0x6698 42: 48 83 f8 06 cmp rax,0x6 46: 0f 84 4c 66 00 00 je 0x6698 ... 666c: 48 81 f8 fe 07 00 00 cmp rax,0x7fe 6673: 0f 1f 40 00 nop DWORD PTR [rax+0x0] 6677: 74 1f je 0x6698 6679: 48 81 f8 ff 07 00 00 cmp rax,0x7ff 6680: 0f 1f 40 00 nop DWORD PTR [rax+0x0] 6684: 74 12 je 0x6698 6686: 48 81 f8 00 08 00 00 cmp rax,0x800 668d: 0f 1f 40 00 nop DWORD PTR [rax+0x0] 6691: 74 05 je 0x6698 6693: 0f 1f 44 00 00 nop DWORD PTR [rax+rax*1+0x0] 6698: b8 02 00 00 00 mov eax,0x2 669d: c9 leave 669e: c3 ret
Since insn 2051~4098 are optimized out right before the padding pass, there are several conditional jumps from the first part are replaced with imm8 jmp_cond, and this triggers the 4 bytes padding, for example at 6673, 6680, and 668d. On the other hand, Insn 2050 is replaced with the 5 bytes nops at 6693.
The third test is to invoke the first and second tests as subprogs to test bpf2bpf. Per the system log, there was one more jit happened with only one pass and the same jit code was produced.
v4: - Add the second test case which triggers jmp_cond padding and imm32 nop jmp padding. - Add the new test case as another subprog
Signed-off-by: Gary Lin glin@suse.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20210119102501.511-4-glin@suse.com (cherry picked from commit 79d1b684e21533bd417df50704a9692830eb8358) Signed-off-by: Wang Yufen wangyufen@huawei.com --- tools/testing/selftests/bpf/test_verifier.c | 72 +++++++++++++++++++++ tools/testing/selftests/bpf/verifier/jit.c | 24 +++++++ 2 files changed, 96 insertions(+)
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index 90c0428bc0e5..cd59e9854e8c 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -297,6 +297,78 @@ static void bpf_fill_scale(struct bpf_test *self) } }
+static int bpf_fill_torturous_jumps_insn_1(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 int bpf_fill_torturous_jumps_insn_2(struct bpf_insn *insn) +{ + unsigned int len = 4100, jmp_off = 2048; + int i, j; + + insn[0] = BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32); + for (i = 1; i <= jmp_off; i++) { + insn[i] = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, i, jmp_off); + } + insn[i++] = BPF_JMP_A(jmp_off); + for (; i <= jmp_off * 2 + 1; i+=16) { + for (j = 0; j < 16; j++) { + insn[i + j] = BPF_JMP_A(16 - j - 1); + } + } + + insn[len - 2] = BPF_MOV64_IMM(BPF_REG_0, 2); + 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_1(insn); + return; + case 2: + self->prog_len = bpf_fill_torturous_jumps_insn_2(insn); + return; + case 3: + /* main */ + insn[i++] = BPF_RAW_INSN(BPF_JMP|BPF_CALL, 0, 1, 0, 4); + insn[i++] = BPF_RAW_INSN(BPF_JMP|BPF_CALL, 0, 1, 0, 262); + insn[i++] = BPF_ST_MEM(BPF_B, BPF_REG_10, -32, 0); + insn[i++] = BPF_MOV64_IMM(BPF_REG_0, 3); + insn[i++] = BPF_EXIT_INSN(); + + /* subprog 1 */ + i += bpf_fill_torturous_jumps_insn_1(insn + i); + + /* subprog 2 */ + i += bpf_fill_torturous_jumps_insn_2(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 = {} */ \ diff --git a/tools/testing/selftests/bpf/verifier/jit.c b/tools/testing/selftests/bpf/verifier/jit.c index c33adf344fae..df215e004566 100644 --- a/tools/testing/selftests/bpf/verifier/jit.c +++ b/tools/testing/selftests/bpf/verifier/jit.c @@ -105,3 +105,27 @@ .result = ACCEPT, .retval = 2, }, +{ + "jit: torturous jumps, imm8 nop jmp and pure jump padding", + .insns = { }, + .fill_helper = bpf_fill_torturous_jumps, + .prog_type = BPF_PROG_TYPE_SCHED_CLS, + .result = ACCEPT, + .retval = 1, +}, +{ + "jit: torturous jumps, imm32 nop jmp and jmp_cond padding", + .insns = { }, + .fill_helper = bpf_fill_torturous_jumps, + .prog_type = BPF_PROG_TYPE_SCHED_CLS, + .result = ACCEPT, + .retval = 2, +}, +{ + "jit: torturous jumps in subprog", + .insns = { }, + .fill_helper = bpf_fill_torturous_jumps, + .prog_type = BPF_PROG_TYPE_SCHED_CLS, + .result = ACCEPT, + .retval = 3, +},