Re: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS tofeature-removal-schedule

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> [...] solution that filters the caller RIP at the generic syscall 
> entry point and checks RCX against the 'expected' SYSCALL 
> instruction address, which is the (per task) vdso-address + 
> constant-offset.

Note that this solution would allow the vsyscall page to be 
'filtered' to the 3 allowed system calls rather efficiently, via a 
second level check.

This second check does not affect the fastpath, and it could be put 
behind a CONFIG_COMPAT_VSYSCALL deprecation define once glibc does 
not put vsyscall references anywhere - but we could even keep it 
around forever, as this way it's defanged permanently.

Thanks,

	Ingo
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