lkml.org 
[lkml]   [2021]   [Apr]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO
    The 04/29/2021 02:23, Bill Wendling wrote:
    > On Thu, Apr 29, 2021 at 12:55 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
    > > The 04/28/2021 12:31, Bill Wendling wrote:
    > > > On Wed, Apr 28, 2021 at 12:21 PM Bill Wendling <morbo@google.com> wrote:
    > > > > On Wed, Apr 28, 2021 at 10:40 AM Mark Brown <broonie@kernel.org> wrote:
    > > > > > On Wed, Apr 28, 2021 at 06:28:47PM +0100, Catalin Marinas wrote:
    > > > > > > On Fri, Apr 23, 2021 at 01:51:59PM -0700, Bill Wendling wrote:
    > > > > >
    > > > > > > > Since the note.gnu.property section in the vDSO is not checked by the
    > > > > > > > dynamic linker, discard the .note.gnu.property sections in the vDSO.
    > > > > >
    > > > > > > Can we not instead fix the linker script to preserve the
    > > > > > > .note.gnu.property, correctly aligned? It doesn't take much space and
    > > > > > > while we don't use it now, it has the BTI information about the binary.
    > > > > >
    > > > > > > Cc'ing a few others who were involved in the BTI support.
    > > > > >
    > > > > > Not just BTI, we also flag PAC usage in there too and could add other
    > > > > > extensions going forwards. While the note isn't actively used by
    > > > > > anything right now due to the kernel mapping the vDSO prior to userspace
    > > > > > starting it is part of the ABI and something could end up wanting to use
    > > > > > it and getting confused if it's not there. It would be much better to
    > > > > > fix the alignment issue.
    > > > >
    > > > > If there's only one of the 8-byte aligned sections guaranteed, we
    > > > > could place it first in the note. Otherwise, we will have to change
    > > > > the alignment of the note (or somehow merge multiple notes).
    > > > >
    > > > I should have clarified that there's only one *entry* in the
    > > > .note.gnu.properties section, and if not then is it possible to merge
    > > > multiple entries into one. (Excuse my ignorance if this is already the
    > > > case.)
    > >
    > > .note.gnu.property should go to PT_GNU_PROPERTY and it
    > > should be merged following rules specified in
    > > https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI
    > > and
    > > https://github.com/ARM-software/abi-aa/blob/master/aaelf64/aaelf64.rst#program-property
    > >
    > > it may also be covered by a (8byte aligned) PT_NOTE, but
    > > that's not a requirement on aarch64 (x86 requires it for
    > > compatibility with old dynamic linker, but since the vdso
    > > is handled specially that may not be relevant either).
    > >
    > > i don't know how this works in linker scripts.
    >
    > This is a potential patch. I haven't had time to test it though.
    > However, it does appear to format the section in the "expected" way,
    > so one's able to grab the build IDs. Thoughts?


    please show the program headers.


    >
    > $ objdump -s -j .note ./arch/arm64/kernel/vdso/vdso.so
    >
    > ./arch/arm64/kernel/vdso/vdso.so: file format elf64-little
    >
    > Contents of section .note:
    > 0288 04000000 10000000 05000000 474e5500 ............GNU.
    > 0298 000000c0 04000000 03000000 00000000 ................
    > 02a8 06000000 04000000 00000000 4c696e75 ............Linu
    > 02b8 78000000 000a0500 06000000 01000000 x...............
    > 02c8 00010000 4c696e75 78000000 00000000 ....Linux.......
    > 02d8 04000000 14000000 03000000 474e5500 ............GNU.
    > 02e8 958db149 af5156cb 45309896 7a53ae8a ...I.QV.E0..zS..
    > 02f8 ef34e95c .4.\
    >
    > diff --git a/arch/arm64/kernel/vdso/vdso.lds.S
    > b/arch/arm64/kernel/vdso/vdso.lds.S
    > index d808ad31e01f..d51e886c6223 100644
    > --- a/arch/arm64/kernel/vdso/vdso.lds.S
    > +++ b/arch/arm64/kernel/vdso/vdso.lds.S
    > @@ -31,7 +31,13 @@ SECTIONS
    > .gnu.version_d : { *(.gnu.version_d) }
    > .gnu.version_r : { *(.gnu.version_r) }
    >
    > - .note : { *(.note.*) } :text :note
    > + /*
    > + * Add the .note.gnu.property section first, as it's aligned to
    > + * 8-bytes, while other notes are aligned to 4-bytes.
    > + */
    > + . = ALIGN(8);
    > +
    > + .note : { *(.note.gnu.property) *(.note.*) } :text :note
    >
    > . = ALIGN(16);

    --

    \
     
     \ /
      Last update: 2021-04-29 11:52    [W:2.344 / U:0.864 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site