Messages in this thread | | | Date | Tue, 9 Jan 2018 17:57:14 -0800 | From | Alexei Starovoitov <> | Subject | Re: [PATCH 16/18] net: mpls: prevent bounds-check bypass via speculative execution |
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On Tue, Jan 09, 2018 at 04:48:24PM -0800, Dan Williams wrote: > > #define __nospec_array_ptr(base, idx, sz) \ > ({ \ > union { typeof(&base[0]) _ptr; unsigned long _bit; } __u; \ > unsigned long _i = (idx); \ > unsigned long _s = (sz); \ > unsigned long _v = (long)(_i | _s - 1 - _i) \ > >> BITS_PER_LONG - 1; \ > unsigned long _mask = _v * ~0UL; \ > OPTIMIZER_HIDE_VAR(_mask); \ > __u._ptr = &base[_i & _mask]; \ > __u._bit &= _mask; \ > __u._ptr; \ > })
_v * ~0UL doesn't seem right and non intuitive. What's wrong with: unsigned long _mask = ~(long)(_i | _s - 1 - _i) >> BITS_PER_LONG - 1;
and why OPTIMIZER_HIDE_VAR ? Could you remove '&' ? since in doesn't work for: struct { int fd[4]; ... } *fdt; it cannot be used as array_acces(fdt->fd, ...);
Could you please drop nospec_ prefix since it is misleading ? This macro doesn't prevent speculation. I think array_access() was the best name so far.
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