Currently, the 64bit relocation value in the instruction
is computed as follows:
__u64 imm = insn[0].imm + ((__u64)insn[1].imm << 32)
Suppose insn[0].imm = -1 (0xffffffff) and insn[1].imm = 1.
With the above computation, insn[0].imm will first sign-extend
to 64bit -1 (0xffffffffFFFFFFFF) and then add 0x1FFFFFFFF,
producing incorrect value 0xFFFFFFFF. The correct value
should be 0x1FFFFFFFF.
Changing insn[0].imm to __u32 first will prevent 64bit sign
extension and fix the issue.
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
tools/lib/bpf/relo_core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/lib/bpf/relo_core.c b/tools/lib/bpf/relo_core.c
index 2ed94daabbe5..f25ffd03c3b1 100644
--- a/tools/lib/bpf/relo_core.c
+++ b/tools/lib/bpf/relo_core.c
@@ -1024,7 +1024,7 @@ int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn,
return -EINVAL;
}
- imm = insn[0].imm + ((__u64)insn[1].imm << 32);
+ imm = (__u32)insn[0].imm + ((__u64)insn[1].imm << 32);
if (res->validate && imm != orig_val) {
pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %llu -> %llu\n",
prog_name, relo_idx,
--
2.30.2
