[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH SpectreV1+L1TF v7 7/9] common/memory: block speculative out-of-bound accesses
The get_page_from_gfn method returns a pointer to a page that belongs to a gfn. Before returning the pointer, the gfn is checked for being valid. Under speculation, these checks can be bypassed, so that the function get_page is still executed partially. Consequently, the function page_get_owner_and_reference might be executed partially as well. In this function, the computed pointer is accessed, resulting in a speculative out-of-bound address load. As the gfn can be controlled by a guest, this access is problematic. To mitigate the root cause, an lfence instruction is added via the evaluate_nospec macro. To make the protection generic, we do not introduce the lfence instruction for this single check, but add it to the mfn_valid function. This way, other potentially problematic accesses are protected as well. This is part of the speculative hardening effort. Signed-off-by: Norbert Manthey <nmanthey@xxxxxxxxx> --- Notes: v7: mention speculative hardening in commit message split return statement into bound check and remainder xen/common/pdx.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/xen/common/pdx.c b/xen/common/pdx.c --- a/xen/common/pdx.c +++ b/xen/common/pdx.c @@ -18,6 +18,7 @@ #include <xen/init.h> #include <xen/mm.h> #include <xen/bitops.h> +#include <xen/nospec.h> /* Parameters for PFN/MADDR compression. */ unsigned long __read_mostly max_pdx; @@ -33,8 +34,9 @@ unsigned long __read_mostly pdx_group_valid[BITS_TO_LONGS( bool __mfn_valid(unsigned long mfn) { - return likely(mfn < max_page) && - likely(!(mfn & pfn_hole_mask)) && + if ( unlikely(evaluate_nospec(mfn >= max_page)) ) + return false; + return likely(!(mfn & pfn_hole_mask)) && likely(test_bit(pfn_to_pdx(mfn) / PDX_GROUP_COUNT, pdx_group_valid)); } -- 2.7.4 Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrer: Christian Schlaeger, Ralf Herbrich Ust-ID: DE 289 237 879 Eingetragen am Amtsgericht Charlottenburg HRB 149173 B _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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