@@ -7,7 +7,7 @@
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
- BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 28),
+ BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 29),
BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
BPF_MOV64_IMM(BPF_REG_9, sizeof(struct test_val)),
BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
@@ -16,6 +16,7 @@
BPF_MOV64_IMM(BPF_REG_4, 256),
BPF_EMIT_CALL(BPF_FUNC_get_stack),
BPF_MOV64_IMM(BPF_REG_1, 0),
+ BPF_JMP32_REG(BPF_JSLT, BPF_REG_0, BPF_REG_1, 20),
BPF_MOV64_REG(BPF_REG_8, BPF_REG_0),
BPF_ALU64_IMM(BPF_LSH, BPF_REG_8, 32),
BPF_ALU64_IMM(BPF_ARSH, BPF_REG_8, 32),
With current ALU32 subreg handling and retval refine fix from last patches we see an expected failure in test_verifier. With verbose verifier state being printed at each step for clarity we have the following relavent lines [I omit register states that are not necessarily useful to see failure cause], #101/p bpf_get_stack return R0 within range FAIL Failed to load prog 'Success'! [..] 14: (85) call bpf_get_stack#67 R0_w=map_value(id=0,off=0,ks=8,vs=48,imm=0) R3_w=inv48 15: R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) 15: (b7) r1 = 0 16: R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) R1_w=inv0 16: (bf) r8 = r0 17: R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) R1_w=inv0 R8_w=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) 17: (67) r8 <<= 32 18: R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) R1_w=inv0 R8_w=inv(id=0,smax_value=9223372032559808512, umax_value=18446744069414584320, var_off=(0x0; 0xffffffff00000000), s32_min_value=0, s32_max_value=0, u32_max_value=0, var32_off=(0x0; 0x0)) 18: (c7) r8 s>>= 32 19 R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) R1_w=inv0 R8_w=inv(id=0,smin_value=-2147483648, smax_value=2147483647, var32_off=(0x0; 0xffffffff)) 19: (cd) if r1 s< r8 goto pc+16 R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) R1_w=inv0 R8_w=inv(id=0,smin_value=-2147483648, smax_value=0, var32_off=(0x0; 0xffffffff)) 20: R0=inv(id=0,smax_value=48,var32_off=(0x0; 0xffffffff)) R1_w=inv0 R8_w=inv(id=0,smin_value=-2147483648, smax_value=0, R9=inv48 20: (1f) r9 -= r8 21: (bf) r2 = r7 22: R2_w=map_value(id=0,off=0,ks=8,vs=48,imm=0) 22: (0f) r2 += r8 value -2147483648 makes map_value pointer be out of bounds After call bpf_get_stack() on line 14 and some moves we have at line 16 an r8 bound with max_value 48 but an unknown min value. This is to be expected bpf_get_stack call can only return a max of the input size but is free to return any negative error in the 32-bit register space. And further C signature returns 'int' which provides no guarantee on the upper 32-bits of the register. Lines 17 and 18 clear the top 32 bits with a left/right shift but use ARSH so we still have worst case min bound before line 19 of -2147483648. At this point the signed check 'r1 s< r8' meant to protect the addition on line 22 where dst reg is a map_value pointer may very well return true with a large negative number. Then the final line 22 will detect this as an invalid operation and fail the program. To fix add a signed less than check to ensure r8 is greater than 0 at line 19 so the bounds check works as expected. Programs _must_ check for negative return codes or they will fail to load now. But on the other hand they were buggy before so for correctness the check really is needed. Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- .../testing/selftests/bpf/verifier/bpf_get_stack.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)