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SubjectRe: ppc elf_map breakage with MAP_FIXED_NOREPLACE
On Tue 13-02-18 12:19:18, Anshuman Khandual wrote:
> On 02/01/2018 07:18 PM, Michal Hocko wrote:
> > On Thu 01-02-18 08:43:34, Anshuman Khandual wrote:
> > [...]
> >> $dmesg | grep elf_brk
> >> [ 9.571192] elf_brk 10030328 elf_bss 10030000
> >>
> >> static int load_elf_binary(struct linux_binprm *bprm)
> >> ---------------------
> >>
> >> if (unlikely (elf_brk > elf_bss)) {
> >> unsigned long nbyte;
> >>
> >> /* There was a PT_LOAD segment with p_memsz > p_filesz
> >> before this one. Map anonymous pages, if needed,
> >> and clear the area. */
> >> retval = set_brk(elf_bss + load_bias,
> >> elf_brk + load_bias,
> >> bss_prot);
> >>
> >>
> >> ---------------------
> >
> > Just a blind shot... Does the following make any difference?
> > ---
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index 021fe78998ea..04b24d00c911 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -895,7 +895,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > the correct location in memory. */
> > for(i = 0, elf_ppnt = elf_phdata;
> > i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
> > - int elf_prot = 0, elf_flags;
> > + int elf_prot = 0, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
> > unsigned long k, vaddr;
> > unsigned long total_size = 0;
> >
> > @@ -927,6 +927,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > */
> > }
> > }
> > + elf_fixed = MAP_FIXED;
> > }
> >
> > if (elf_ppnt->p_flags & PF_R)
> > @@ -944,7 +945,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > * the ET_DYN load_addr calculations, proceed normally.
> > */
> > if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
> > - elf_flags |= MAP_FIXED_NOREPLACE;
> > + elf_flags |= elf_fixed;
> > } else if (loc->elf_ex.e_type == ET_DYN) {
> > /*
> > * This logic is run once for the first LOAD Program
> > @@ -980,7 +981,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > load_bias = ELF_ET_DYN_BASE;
> > if (current->flags & PF_RANDOMIZE)
> > load_bias += arch_mmap_rnd();
> > - elf_flags |= MAP_FIXED_NOREPLACE;
> > + elf_flags |= elf_fixed;
> > } else
> > load_bias = 0;
> >
> >
>
> Yeah, it does solve the problem on mmotm-2018-01-25-16-20.

Thanks a lot for testing! I will post an RFC patch shortly.

--
Michal Hocko
SUSE Labs

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