4.14-stable review patch. If anyone has any objections, please let me know.
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From: Dave Hansen dave.hansen@linux.intel.com
commit c313ec66317d421fb5768d78c56abed2dc862264 upstream.
Global pages stay in the TLB across context switches. Since all contexts share the same kernel mapping, these mappings are marked as global pages so kernel entries in the TLB are not flushed out on a context switch.
But, even having these entries in the TLB opens up something that an attacker can use, such as the double-page-fault attack:
http://www.ieee-security.org/TC/SP2013/papers/4977a191.pdf
That means that even when PAGE_TABLE_ISOLATION switches page tables on return to user space the global pages would stay in the TLB cache.
Disable global pages so that kernel TLB entries can be flushed before returning to user space. This way, all accesses to kernel addresses from userspace result in a TLB miss independent of the existence of a kernel mapping.
Suppress global pages via the __supported_pte_mask. The user space mappings set PAGE_GLOBAL for the minimal kernel mappings which are required for entry/exit. These mappings are set up manually so the filtering does not take place.
[ The __supported_pte_mask simplification was written by Thomas Gleixner. ] Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Borislav Petkov bp@suse.de Cc: Andy Lutomirski luto@kernel.org Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: David Laight David.Laight@aculab.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: Eduardo Valentin eduval@amazon.com Cc: Greg KH gregkh@linuxfoundation.org Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Juergen Gross jgross@suse.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Will Deacon will.deacon@arm.com Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Cc: linux-mm@kvack.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/mm/init.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -161,6 +161,12 @@ struct map_range {
static int page_size_mask;
+static void enable_global_pages(void) +{ + if (!static_cpu_has(X86_FEATURE_PTI)) + __supported_pte_mask |= _PAGE_GLOBAL; +} + static void __init probe_page_size_mask(void) { /* @@ -179,11 +185,11 @@ static void __init probe_page_size_mask( cr4_set_bits_and_update_boot(X86_CR4_PSE);
/* Enable PGE if available */ + __supported_pte_mask &= ~_PAGE_GLOBAL; if (boot_cpu_has(X86_FEATURE_PGE)) { cr4_set_bits_and_update_boot(X86_CR4_PGE); - __supported_pte_mask |= _PAGE_GLOBAL; - } else - __supported_pte_mask &= ~_PAGE_GLOBAL; + enable_global_pages(); + }
/* Enable 1 GB linear kernel mappings if available: */ if (direct_gbpages && boot_cpu_has(X86_FEATURE_GBPAGES)) {