[PATCH v7 0/4] arm64: Enable BTI for the executable as well as the interpreter

[Adhemerval Zanella]

On 17/01/2022 14:54, Catalin Marinas via Libc-alpha wrote:
> On Fri, Jan 07, 2022 at 12:01:17PM +0000, Catalin Marinas wrote:
>> I think we can look at this from two angles:
>>
>> 1. Ignoring MDWE, should whoever does the original mmap() also honour
>>    PROT_BTI? We do this for static binaries but, for consistency, should
>>    we extend it to dynamic executable?
>>
>> 2. A 'simple' fix to allow MDWE together with BTI.
> 
> Thinking about it, (1) is not that different from the kernel setting
> PROT_EXEC on the main executable when the dynamic loader could've done
> it as well. There is a case for making this more consistent: whoever
> does the mmap() should use the full attributes.
> 
> Question for the toolchain people: would the compiler ever generate
> relocations in the main executable that the linker needs to resolve via
> an mprotect(READ|WRITE) followed by mprotect(READ|EXEC)? If yes, we'd
> better go for a proper MDWE implementation in the kernel.
> 

Yes, text relocations.  However these are deprecated (some libcs even do
not support it) and have a lot of drawbacks.