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bpf: Fix register equivalence tracking.

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The 64-bit JEQ/JNE handling in reg_set_min_max() was clearing reg->id in either
true or false branch. In the case 'if (reg->id)' check was done on the other
branch the counter part register would have reg->id == 0 when called into
find_equal_scalars(). In such case the helper would incorrectly identify other
registers with id == 0 as equivalent and propagate the state incorrectly.
Fix it by preserving ID across reg_set_min_max().

In other words any kind of comparison operator on the scalar register
should preserve its ID to recognize:

r1 = r2
if (r1 == 20) {
  #1 here both r1 and r2 == 20
} else if (r2 < 20) {
  #2 here both r1 and r2 < 20
}

The patch is addressing #1 case. The #2 was working correctly already.

Fixes: 75748837b7 ("bpf: Propagate scalar ranges through register assignments.")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Tested-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201014175608.1416-1-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov
2020-10-14 10:56:08 -07:00
committed by Daniel Borkmann
parent ccdf7fae3a
commit e688c3db7c
2 changed files with 51 additions and 13 deletions
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26
tools/testing/selftests/bpf/verifier/regalloc.c
View File

@@ -241,3 +241,29 @@
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_TRACEPOINT,
},
{
"regalloc, spill, JEQ",
.insns = {
BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_0, -8), /* spill r0 */
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 0),
/* The verifier will walk the rest twice with r0 == 0 and r0 == map_value */
BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_2, 20, 0),
/* The verifier will walk the rest two more times with r0 == 20 and r0 == unknown */
BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_10, -8), /* fill r3 with map_value */
BPF_JMP_IMM(BPF_JEQ, BPF_REG_3, 0, 1), /* skip ldx if map_value == NULL */
/* Buggy verifier will think that r3 == 20 here */
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_3, 0), /* read from map_value */
BPF_EXIT_INSN(),
},
.fixup_map_hash_48b = { 4 },
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_TRACEPOINT,
},