On 5/9/22 3:37 PM, Andrii Nakryiko wrote:
On Sun, May 1, 2022 at 12:00 PM Yonghong Song <yhs@xxxxxx> wrote: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);great catch, it should also probably be written as | instead of + operation?
The '|' also works. I used '|' in other places, so will change to use '|' as well.
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
