On Thu, Nov 22, 2018 at 12:01:54PM +0000, Dave Martin wrote:
> On Mon, Nov 19, 2018 at 05:25:12PM +0100, Vincent Whitchurch wrote:
> > st_info is currently overwritten after relocation and used to store the
> > elf_type(). However, we're going to need it fix kallsyms on ARM's
> > Thumb-2 kernels, so preserve st_info and overwrite the st_size field
> > instead. st_size is neither used by the module core nor by any
> > architecture.
> >
> > Signed-off-by: Vincent Whitchurch <vincent.whitchu...@axis.com>
> > ---
> > v4: Split out to separate patch. Use st_size instead of st_other.
> > v1-v3: See PATCH 2/2
> >
> > kernel/module.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 49a405891587..3d86a38b580c 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -2682,7 +2682,7 @@ static void add_kallsyms(struct module *mod, const
> > struct load_info *info)
> >
> > /* Set types up while we still have access to sections. */
> > for (i = 0; i < mod->kallsyms->num_symtab; i++)
> > - mod->kallsyms->symtab[i].st_info
> > + mod->kallsyms->symtab[i].st_size
> > = elf_type(&mod->kallsyms->symtab[i], info);
> >
> > /* Now populate the cut down core kallsyms for after init. */
> > @@ -4061,7 +4061,7 @@ int module_get_kallsym(unsigned int symnum, unsigned
> > long *value, char *type,
> > kallsyms = rcu_dereference_sched(mod->kallsyms);
> > if (symnum < kallsyms->num_symtab) {
> > *value = kallsyms->symtab[symnum].st_value;
> > - *type = kallsyms->symtab[symnum].st_info;
> > + *type = kallsyms->symtab[symnum].st_size;
> > strlcpy(name, symname(kallsyms, symnum), KSYM_NAME_LEN);
> > strlcpy(module_name, mod->name, MODULE_NAME_LEN);
> > *exported = is_exported(name, *value, mod);
>
> This is fine if st_size is really unused, but how sure are you of that?
>
> grepping for st_size throws up some hits that appear ELF-related, but
> I've not investigated them in detail.
>
> (The fact that struct stat has an identically named field throws up
> a load of false positives too.)
$ git describe --tags
v4.20-rc3-93-g92b419289cee
$ rg -m1 '[\.>]st_size' --iglob '!**/tools/**' --iglob '!**/vdso*' --iglob
'!**/scripts/**' --iglob '!**/usr/**' --iglob '!**/samples/**' | cat
| kernel/kexec_file.c: if (sym->st_size != size) {
Symbols in kexec kernel.
| fs/stat.c: tmp.st_size = stat->size;
| Documentation/networking/tls.txt: sendfile(sock, file, &offset,
stat.st_size);
| net/9p/client.c: ret->st_rdev, ret->st_size, ret->st_blksize,
| net/9p/protocol.c: &stbuf->st_rdev,
&stbuf->st_size,
| fs/9p/vfs_inode_dotl.c: i_size_write(inode, stat->st_size);
| fs/hostfs/hostfs_user.c: p->size = buf->st_size;
| arch/powerpc/boot/mktree.c: nblks = (st.st_size + IMGBLK) / IMGBLK;
| arch/alpha/kernel/osf_sys.c: tmp.st_size = lstat->size;
| arch/x86/ia32/sys_ia32.c: __put_user(stat->size, &ubuf->st_size) ||
Not Elf_Sym.
| arch/x86/kernel/machine_kexec_64.c: sym->st_size);
Symbols in kexec kernel.
| arch/sparc/boot/piggyback.c: st4(buffer + 12, s.st_size);
| arch/sparc/kernel/sys_sparc32.c: err |= put_user(stat->size,
&statbuf->st_size);
| arch/um/os-Linux/file.c: .ust_size = src->st_size, /*
total size, in bytes */
| arch/um/os-Linux/start_up.c: size = (buf.st_size + UM_KERN_PAGE_SIZE) &
~(UM_KERN_PAGE_SIZE - 1);
| arch/s390/kernel/compat_linux.c: tmp.st_size = stat->size;
| arch/arm/kernel/sys_oabi-compat.c: tmp.st_size = stat->size;
| arch/mips/boot/compressed/calc_vmlinuz_load_addr.c: vmlinux_size =
(uint64_t)sb.st_size;
| drivers/net/ethernet/marvell/sky2.c: hw->st_idx =
RING_NEXT(hw->st_idx, hw->st_size);
Not Elf_Sym.
