On 30.03.2022 19:04, Roger Pau Monné wrote: > On Wed, Mar 30, 2022 at 01:05:31PM +0200,>> --- a/xen/arch/x86/livepatch.c >> +++ b/xen/arch/x86/livepatch.c >> @@ -157,9 +157,15 @@ void noinline arch_livepatch_apply(struc >> * loaded hotpatch (to avoid racing against other fixups adding/removing >> * ENDBR64 or similar instructions). >> */ >> - if ( is_endbr64(old_ptr) || is_endbr64_poison(func->old_addr) ) >> + if ( len >= ENDBR64_LEN && > > Sorry, didn't realize before, but shouldn't this check be using > old_size instead of len (which is based on new_size)?
Yes and no: In principle yes, but with len == func->new_size in the NOP case, and with arch_livepatch_verify_func() guaranteeing new_size <= old_size, the check is still fine for that case. Plus: If new_size was less than 4 _but_ there's an ENDBR64 at the start, what would we do? I think there's more that needs fixing in this regard. So I guess I'll make a v3 with this extra fix dropped and with the livepatch_insn_len() invocation simply moved. After all the primary goal is to get the stable trees unstuck. Jan
