Messages in this thread | | | Date | Thu, 29 Apr 2021 08:54:55 +0100 | From | Szabolcs Nagy <> | Subject | Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO |
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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.
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