summaryrefslogtreecommitdiffstats
path: root/arch
diff options
context:
space:
mode:
authorDave Hansen <dave.hansen@linux.intel.com>2017-12-04 15:07:34 +0100
committerIngo Molnar <mingo@kernel.org>2017-12-23 21:12:59 +0100
commitc313ec66317d421fb5768d78c56abed2dc862264 (patch)
treee5e7ccc22126fbe6b516e6c135e1be247dae6b00 /arch
parenta89f040fa34ec9cd682aed98b8f04e3c47d998bd (diff)
downloadlinux-c313ec66317d421fb5768d78c56abed2dc862264.tar.bz2
x86/mm/pti: Disable global pages if PAGE_TABLE_ISOLATION=y
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/mm/init.c12
1 files 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)) {