Re: [PATCH] elf: Align argument of __munmap to page size [BZ #28676]

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, Dec 14, 2021 at 6:24 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > On Mon, Dec 13, 2021 at 11:40 PM Florian Weimer <fweimer@redhat.com> wrote:
> >>
> >> * H. J. Lu via Libc-alpha:
> >>
> >> > On Mon, Dec 13, 2021 at 6:49 PM Rongwei Wang
> >> > <rongwei.wang@linux.alibaba.com> wrote:
> >> >>
> >> >> Hi, HJ
> >> >>
> >> >> Thanks for your help to fix this bug. And I just found out that the
> >> >> patch "elf: Properly align PT_LOAD segments" had been merged into
> >> >> glibc/master.
> >> >>
> >> >> And I saw Florian's email:
> >> >>
> >> >>  > We should check munmap failure though and rollback everything if
> >> >>  > necessary.  It's possible we can undo the initial PROT_NONE mapping even
> >> >>  > if future munmap calls fail because unmapping the first mapping does not
> >> >>  > need to split a mapping.
> >> >>
> >> >> It seems rollback initial PROT_NONE mapping when munmap fails is good
> >> >> idea. Nice to have. Of course, IMO, this your patch is also can fix this
> >> >> munmap failure well. what do you think?
> >> >>
> >> >> When this fix is stable in glibc upstream, I will backport it into our
> >> >> internal glibc repo. So, if you have any improve this fix suggestions, I
> >> >> will respond immediately. Sorry for my speed is much slower than your.
> >> >>
> >> >>
> >> >
> >> > Let's wait for a few days.
> >>
> >> Can we please fix the regression in some way?  It impacts development,
> >> particularly at this late stage during the 2.34 cycle.
> >>
> >> Either revert the change, or at least add the unchecked __munmap, and
> >> fix that later.
> >
> > What is the unchecked __munmap?
>
> The __munmap at the end:
>
> diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
> index 70a4c40695..54e606aa87 100644
> --- a/elf/dl-map-segments.h
> +++ b/elf/dl-map-segments.h
> @@ -55,6 +55,7 @@ _dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
>        if (delta)
>         __munmap ((void *) map_start, delta);
>        ElfW(Addr) map_end = map_start_aligned + maplength;
> +      map_end = ALIGN_UP (map_end, GLRO(dl_pagesize));
>        delta = map_start + maplen - map_end;
>        if (delta)
>         __munmap ((void *) map_end, delta);
>

This is

https://sourceware.org/pipermail/libc-alpha/2021-December/134097.html

I am checking it in now.

Thanks.

-- 
H.J.