Messages in this thread Patch in this message | | | From | Bill Wendling <> | Date | Thu, 29 Apr 2021 11:52:26 -0700 | Subject | Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO |
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On Thu, Apr 29, 2021 at 2:50 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote: > 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. >
$ 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
Section to Segment mapping: Segment Sections... 00 .hash .dynsym .dynstr .gnu.version .gnu.version_d .note .text .eh_frame_hdr .eh_frame .dynamic 01 .dynamic 02 .note 03 .eh_frame_hdr .eh_frame
> > > > $ 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); > > --
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