On Tue, Mar 08, 2022 at 04:45:34PM +0100, Jan Beulich wrote: > On 08.03.2022 16:36, Bjoern Doebel wrote: > > --- a/xen/arch/x86/livepatch.c > > +++ b/xen/arch/x86/livepatch.c > > @@ -339,7 +339,7 @@ int arch_livepatch_perform_rela(struct livepatch_elf > > *elf, > > > > val -= (uint64_t)dest; > > *(int32_t *)dest = val; > > Afaict after this assignment ... > > > - if ( (int64_t)val != *(int32_t *)dest ) > > + if ( (int32_t)val != *(int32_t *)dest ) > > ... this condition can never be false. The cast really wants to be > to int64_t, and the overflow you saw being reported is quite likely > for a different reason. But from the sole message you did quote > it's not really possible to figure what else is wrong.
It seems Linux has that check ifdef'ed [0], but there's no reference as to why it's that way (I've tracked it back to the x86-64 import on the historical tree, f3081f5b66a06175ff2dabfe885a53fb04e71076). It's a 64bit relocation using a 32bit value, but it's unclear to me that modifying the top 32bits is not allowed/intended. Regards, Roger. [0] https://elixir.bootlin.com/linux/latest/source/arch/x86/kernel/module.c#L190
