Re: [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late relocations

Josh Poimboeuf
2020-04-24T04:12:13Z

On Thu, Apr 23, 2020 at 10:35:21PM -0400, Joe Lawrence wrote:
> > diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
> > index 2798329ebb74..fe446f42818f 100644
> > --- a/arch/s390/kernel/module.c
> > +++ b/arch/s390/kernel/module.c
> > @@ -297,7 +297,7 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
> >
> > gotent = me->core_layout.base + me->arch.got_offset +
> > info->got_offset;
> > - *gotent = val;
> > + write(gotent, &val, sizeof(*gotent));
> > info->got_initialized = 1;
> > }
> > val = info->got_offset + rela->r_addend;
> > @@ -330,25 +330,29 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
> > case R_390_PLTOFF32: /* 32 bit offset from GOT to PLT. */
> > case R_390_PLTOFF64: /* 16 bit offset from GOT to PLT. */
> > if (info->plt_initialized == 0) {
> > - unsigned int *ip;
> > + unsigned int *ip, insn[5];
> > +
> > ip = me->core_layout.base + me->arch.plt_offset +
> > info->plt_offset;
>
> Would it be too paranoid to declare:
>
> const unsigned int *ip = me->core_layout.base +
> me->arch.plt_offset +
> info->plt_offset;
>
> That would trip an assignment to read-only error if someone were tempted
> to write directly through the pointer in the future. Ditto for Elf_Addr
> *gotent pointer in the R_390_GOTPLTENT case.

The only problem is then the write() triggers a warning because then we
*are* trying to write through the pointer :-)

arch/s390/kernel/module.c:300:10: warning: passing argument 1 of ‘write’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
300 | write(gotent, &val, sizeof(*gotent));

--
Josh