On Tue, Jun 15, 2021 at 07:51:07PM +0100, Edward Cree wrote: > > As I understand it, the UBSAN report is coming from the eBPF interpreter, > which is the *slow path* and indeed on many production systems is > compiled out for hardening reasons (CONFIG_BPF_JIT_ALWAYS_ON). > Perhaps a better approach to the fix would be to change the interpreter > to compute "DST = DST << (SRC & 63);" (and similar for other shifts and > bitnesses), thus matching the behaviour of most chips' shift opcodes. > This would shut up UBSAN, without affecting JIT code generation. > Yes, I suggested that last week (https://lkml.kernel.org/netdev/YMJvbGEz0xu9JU9D@xxxxxxxxx). The AND will even get optimized out when compiling for most CPUs. - Eric
