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Re: [PATCH 0/2] aarch64: Enable pointer auth in PLT
On 24/06/2019 14:50, Szabolcs Nagy wrote:
> On 24/06/2019 17:28, Florian Weimer wrote:
>> * Szabolcs Nagy:
>>
>>> there is no easy way to mark binaries such that
>>> old loader rejects them if it does not understand
>>> the marking.
>>
>> There are symbol versions, new relocation types, and EI_ABIVERSION.
>> For the latter, see libc-abis.
>
> bumping EI_ABIVERSION may work for pac-plt, i'll look
> into it (that will have to be documented in the elf abi).
>
> an alternative is to leave the elf abi as is and solve this
> in the bfd linker by -z pac-plt implying -u __pac_plt_supported
> and adding __pac_plt_supported symbol to glibc.
> (i.e. only solve this in the tooling, the magic symbol
> ref is not required by the elf abi, just a safety net
> provided by the binutils implementation, a huge hack,
> but in practice it should be enough)
I will follow the EI_ABIVERSION path since it changes how loader
handles the PLTs (similar to IFUNC).
If I understood correctly, the idea is just to prevent prevent
old-loaders to fail for binaries built with -z pac-plt, wouldn't it
happen anyway when kernel has pac enabled? Would it to make the
failure more explicit (by printing a error message) or to just
avoid ld.so to load it altogether?