Re: [Xen-devel] [PATCH 2/2] xen/livepatch: Don't crash on encountering STN_UNDEF relocations

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.06.17 at 22:51, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/livepatch.c
> +++ b/xen/arch/x86/livepatch.c
> @@ -170,14 +170,22 @@ int arch_livepatch_perform_rela(struct livepatch_elf 
> *elf,
>          uint8_t *dest = base->load_addr + r->r_offset;
>          uint64_t val;
>  
> -        if ( symndx > elf->nsym )
> +        if ( symndx == STN_UNDEF )
> +            val = 0;
> +        else if ( symndx > elf->nsym )
>          {
>              dprintk(XENLOG_ERR, LIVEPATCH "%s: Relative relocation wants 
> symbol@%u which is past end!\n",
>                      elf->name, symndx);
>              return -EINVAL;
>          }
> -
> -        val = r->r_addend + elf->sym[symndx].sym->st_value;
> +        else if ( !elf->sym[symndx].sym )
> +        {
> +            dprintk(XENLOG_ERR, LIVEPATCH "%s: No symbol@%u\n",
> +                    elf->name, symndx);
> +            return -EINVAL;
> +        }
> +        else
> +            val = r->r_addend + elf->sym[symndx].sym->st_value;

I don't understand this: st_value for STN_UNDEF is going to be zero
(so far there's also no extension defined for the first entry, afaict),
so there should be no difference between hard-coding the zero and
reading the symbol table entry. Furthermore r_addend would still
need applying. And finally "val" is never being cast to a pointer, and
hence I miss the connection to whatever crash you've been
observing.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel