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

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>

1 files changed, 19 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/verifier/jit.c b/tools/testing/selftests/bpf/verifier/jit.c
index be488b4495a3..c33adf344fae 100644
--- a/tools/testing/selftests/bpf/verifier/jit.c
+++ b/tools/testing/selftests/bpf/verifier/jit.c
@@ -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,
+},