On 01/10/2019 11:45, Jan Beulich wrote:
> On 30.09.2019 20:24, Andrew Cooper wrote:
>> --- a/xen/common/Kconfig
>> +++ b/xen/common/Kconfig
>> @@ -77,6 +77,27 @@ config HAS_CHECKPOLICY
>> string
>> option env="XEN_HAS_CHECKPOLICY"
>>
>> +menu "Speculative hardening"
>> +
>> +config SPECULATIVE_ARRAY_HARDEN
> Seeing also the new item in patch 2 - wouldn't it be better for them all
> to have (just) a common prefix, rather than common prefix and a common
> suffix. E.g. SPECULATIVE_HARDEN_ARRAYS here and SPECULATIVE_HARDEN_BRANCHES
> there?
Can do.
>
>> --- a/xen/include/xen/nospec.h
>> +++ b/xen/include/xen/nospec.h
>> @@ -33,6 +33,7 @@ static inline unsigned long
>> array_index_mask_nospec(unsigned long index,
>> }
>> #endif
>>
>> +#ifdef CONFIG_SPECULATIVE_ARRAY_HARDEN
>> /*
>> * array_index_nospec - sanitize an array index after a bounds check
>> *
>> @@ -58,6 +59,17 @@ static inline unsigned long
>> array_index_mask_nospec(unsigned long index,
>> \
>> (typeof(_i)) (_i & _mask); \
>> })
>> +#else
>> +/* No index hardening. */
>> +#define array_index_nospec(index, size) \
>> +({ \
>> + typeof(index) _i = (index); \
>> + typeof(size) _s = (size); \
>> + \
>> + (void)_s; \
>> + _i; \
>> +})
> Why not the simpler
>
> #define array_index_nospec(index, size) \
> ({ \
> (void)(size); \
> (index); \
> })
>
> at which point it would seem feasible to avoid the use of compiler
> extensions altogether by making it
>
> #define array_index_nospec(index, size) ((void)(size), (index))
Huh - I tried that first, and GCC was distinctly unhappy. It turns out
to be the bracketing of size, which when omitted, causes:
/local/xen.git/xen/include/xen/nospec.h:66:42: error: void value not
ignored as it ought to be
#define array_index_nospec(index, size) ((void)size, (index))
argo.c:2174:16: note: in expansion of macro ‘array_index_nospec’
niov = array_index_nospec(arg3, XEN_ARGO_MAXIOV + 1);
^~~~~~~~~~~~~~~~~~
I'll switch to this version.
~Andrew
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