Re: [PATCH] bpf, x32: Fix bug for BPF_JMP | {BPF_JSGT, BPF_JSLE, BPF_JSLT, BPF_JSGE}

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On 11/21/19 8:43 AM, Wang YanQing wrote:
commit 711aef1bbf88212a21f7103e88f397b47a528805 upstream.

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.

Note:
The original commit adds a testcase in selftests/bpf for such bug, this
backport patch doesn't include the testcase, because the testcase needs
another upstream commit.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=205469
Reported-by: Tony Ambardar <itugrok@xxxxxxxxx>
Cc: Tony Ambardar <itugrok@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx #v4.19
Signed-off-by: Wang YanQing <udknight@xxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>

Thanks a lot for backporting & testing, Wang, much appreciated! Greg, if you get a
chance, please queue this & the other stable requests from Wang up.

Thanks,
Daniel



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