linux-kernel - Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO

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Date:   Fri, 30 Apr 2021 01:29:12 -0700
From:   Bill Wendling <morbo@...gle.com>
To:     Szabolcs Nagy <szabolcs.nagy@....com>
Cc:     Mark Brown <broonie@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Kees Cook <keescook@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Will Deacon <will@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Daniel Kiss <Daniel.Kiss@....com>
Subject: Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO

On Fri, Apr 30, 2021 at 1:17 AM Szabolcs Nagy <szabolcs.nagy@....com> wrote:
> The 04/29/2021 11:52, Bill Wendling wrote:
> > $ readelf -lW arch/arm64/kernel/vdso/vdso.so
> >
> > Elf file type is DYN (Shared object file)
> > Entry point 0x300
> > There are 4 program headers, starting at offset 64
> >
> > Program Headers:
> >   Type           Offset   VirtAddr           PhysAddr
> > FileSiz  MemSiz   Flg Align
> >   LOAD           0x000000 0x0000000000000000 0x0000000000000000
> > 0x000968 0x000968 R E 0x8
> >   DYNAMIC        0x0008a8 0x00000000000008a8 0x00000000000008a8
> > 0x0000c0 0x0000c0 R   0x8
> >   NOTE           0x000288 0x0000000000000288 0x0000000000000288
> > 0x000074 0x000074 R   0x8
> >   GNU_EH_FRAME   0x0008a4 0x00000000000008a4 0x00000000000008a4
> > 0x000000 0x000000 R E 0x1
>
> this is wrong because the abi specifically says properties
> are in PT_GNU_PROPERTY, not in PT_NOTE.
>
Right. The issue is more complex than this fix is meant for, to be
honest. That is, it seems that there needs to be a generalized way of
handling the different .note sections.

-bw

> so the original patch that removes them from notes is fine,
> but ideally they should be readded under PT_GNU_PROPERTY.
>
> (x86 needs it there too, but also needs it under PT_NOTE for
> historical reasons. ideally the section would have been named
> other than .note and was not marked as SHF_NOTE, because
> properties are merged completely differently by the linker
> than notes, so now linkers have to special case it by section
> name. properties should have been designed like the
>  .ARM.attributes section except that is not in a load segment
> and thus has no runtime semantics while the key feature of
> properties is the runtime semantics. however accessing the
> program headers of the vdso is not trivial at runtime from
> user code so dropping the properties might work too, but can
> bite us in the future depending on how they evolve: the ld.so
> can look at vdso program headers.)