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

I asked Andi whether 64-bit processes are allowed to make 32-bit
syscalls on May 4 2007, and he stated that yes it's both allowed
and supposed to work. (The thread was cc:d to discuss@x86-64.org.)

> --- linux-2.6.26.2.orig/arch/x86/ia32/ia32entry.S 2008-08-06 09:19:01.000000000 -0700
> +++ linux-2.6.26.2/arch/x86/ia32/ia32entry.S 2008-08-06 13:34:54.566992000 -0700
> @@ -123,6 +123,8 @@
> .quad 1b,ia32_badarg
> .previous
> GET_THREAD_INFO(%r10)
> + testl $_TIF_IA32,threadinfo_flags(%r10)
> + jz ia32_bad_abi
> orl $TS_COMPAT,threadinfo_status(%r10)
> testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),threadinfo_flags(%r10)
> CFI_REMEMBER_STATE
> @@ -230,6 +232,8 @@
> .quad 1b,ia32_badarg
> .previous
> GET_THREAD_INFO(%r10)
> + testl $_TIF_IA32,threadinfo_flags(%r10)
> + jz ia32_bad_abi
> orl $TS_COMPAT,threadinfo_status(%r10)
> testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),threadinfo_flags(%r10)
> CFI_REMEMBER_STATE
> @@ -324,6 +328,8 @@
> this could be a problem. */
> SAVE_ARGS 0,0,1
> GET_THREAD_INFO(%r10)
> + testl $_TIF_IA32,threadinfo_flags(%r10)
> + jz ia32_bad_abi
> orl $TS_COMPAT,threadinfo_status(%r10)
> testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),threadinfo_flags(%r10)
> jnz ia32_tracesys

Your patch slows down all compat-mode syscalls.

/Mikael


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