Re: [PATCH] x86: prevent binaries from making system calls using the wrong syscall interface

[Andi Kleen <andi@firstfloor.org>]

md@google.com (Michael Davidson) writes:

> Prevent binaries from making system calls using other than one
> of the "normal" system call interfaces for that binary type.
>
> Currently there is nothing to prevent 64 bit binaries from
> attempting to make system calls using the 32 bit system call
> interfaces and vice versa.

nack. That was allowed intentionally because there are some
use cases for 32bit syscalls from 64bit (e.g. 64bit JIT running 
32bit executable). I believe it is used in production in 
a few cases.

>
> Since the 32 bit and 64 bit system call numbers are different
> this means that a binary could attempt to obfuscate which system
> calls it was actually making by using the "wrong" system call
> interface. In particular, the call to audit_syscall_entry()
> relies on checking the TIF_IA32 flag to determine whether it is
> dealing with a 32 or 64 bit system call without regard to the
> actual type of system call that was made.While this specific issue
> could be addressed by checking the TS_COMPAT flag in threadinfo_status
> it seems preferable to simply disallow this situation altogether.

audit is wrong to assume this and should be just fixed 

-Andi