[kernel-hardening] Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

["H. Peter Anvin" <hpa@zytor.com>]

On 02/16/2012 07:53 PM, Will Drewry wrote:
> 
> An earlier change Roland had prodded me toward was adding a
> syscall_get_arch() call to asm/syscall.h which returned the
> appropriate audit arch value for the current calling convention.  I
> hate to suggest this, but should I go ahead and wire that up for x86
> now, make it a dependency for HAVE_ARCH_SECCOMP_FILTER (and officially
> part of asm/syscall.h) then let it trickle into existence?  Maybe
> something like:
> 

... and we have been talking about making a regset and export it to
ptrace and core dumps, too.

> static inline int syscall_get_arch(struct task_struct *task, struct
> pt_regs *regs)
> {
> #ifdef CONFIG_IA32_EMULATION
>   if (task_thread_info(task)->status & TS_COMPAT)
>     return AUDIT_ARCH_I386;
> #endif
> #ifdef CONFIG_64BIT
>   return AUDIT_ARCH_X86_64;
> #else
>   return AUDIT_ARCH_I386;
> #endif
> }
> 

In this case it could be is_compat_task().

> There would be no other callers, though, because everywhere AUDIT_ARCH
> is used it is hardcoded as appropriate.  Then when x32 comes along, it
> can figure out where it belongs using tif status and/or regs.

For x32 you have the option of introducing a new value or relying on bit
30 in eax (and AUDIT_ARCH_X86_64).  The latter is more natural, probably.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.