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bpf, x32: Fix bug for BPF_JMP | {BPF_JSGT, BPF_JSLE, BPF_JSLT, BPF_JSGE}

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The current method to compare 64-bit numbers for conditional jump is:

1) Compare the high 32-bit first.

2) If the high 32-bit isn't the same, then goto step 4.

3) Compare the low 32-bit.

4) Check the desired condition.

This method is right for unsigned comparison, but it is buggy for signed
comparison, because it does signed comparison for low 32-bit too.

There is only one sign bit in 64-bit number, that is the MSB in the 64-bit
number, it is wrong to treat low 32-bit as signed number and do the signed
comparison for it.

This patch fixes the bug and adds a testcase in selftests/bpf for such bug.

Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Wang YanQing
2019-04-27 16:28:26 +08:00
committed by Daniel Borkmann
parent 886b7a5010
commit 711aef1bbf
2 changed files with 185 additions and 51 deletions
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19
tools/testing/selftests/bpf/verifier/jit.c
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@@ -86,3 +86,22 @@
.result = ACCEPT,
.retval = 2,
},
{
"jit: jsgt, jslt",
.insns = {
BPF_LD_IMM64(BPF_REG_1, 0x80000000ULL),
BPF_LD_IMM64(BPF_REG_2, 0x0ULL),
BPF_JMP_REG(BPF_JSGT, BPF_REG_1, BPF_REG_2, 2),
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_EXIT_INSN(),
BPF_JMP_REG(BPF_JSLT, BPF_REG_2, BPF_REG_1, 2),
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_EXIT_INSN(),
BPF_MOV64_IMM(BPF_REG_0, 2),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
.retval = 2,
},