From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Mon, 4 Dec 2017 15:07:34 +0100 Subject: [PATCH] x86/mm/pti: Disable global pages if PAGE_TABLE_ISOLATION=y MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CVE-2017-5754 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 Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Andy Lutomirski Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Brian Gerst Cc: David Laight Cc: Denys Vlasenko Cc: Eduardo Valentin Cc: Greg KH Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Will Deacon 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 (cherry picked from commit c313ec66317d421fb5768d78c56abed2dc862264) Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit ace78e99d765da1e59f6b151adac6c360c67af7d) Signed-off-by: Fabian Grünbichler --- arch/x86/mm/init.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index a22c2b95e513..020223420308 100644 --- 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(void) 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)) { -- 2.14.2