Revert "x86/mm/legacy: Populate the user page-table with user pgd's"

This reverts commit 1f40a46cf47c12d93a5ad9dccd82bd36ff8f956a.

It turned out that this patch is not sufficient to enable PTI on 32 bit
systems with legacy 2-level page-tables. In this paging mode the huge-page
PTEs are in the top-level page-table directory, where also the mirroring to
the user-space page-table happens. So every huge PTE exits twice, in the
kernel and in the user page-table.

That means that accessed/dirty bits need to be fetched from two PTEs in
this mode to be safe, but this is not trivial to implement because it needs
changes to generic code just for the sake of enabling PTI with 32-bit
legacy paging. As all systems that need PTI should support PAE anyway,
remove support for PTI when 32-bit legacy paging is used.

Fixes: 7757d607c6b3 ('x86/pti: Allow CONFIG_PAGE_TABLE_ISOLATION for x86_32')
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Cc: linux-mm@kvack.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Link: https://lkml.kernel.org/r/1536922754-31379-1-git-send-email-joro@8bytes.org

diff --git a/arch/x86/include/asm/pgtable-2level.h b/arch/x86/include/asm/pgtable-2level.h
index 24c6cf5f16b72eb536a9ee279b15e54f0d22af80..60d0f90153178b3fb104360536854d676f7429ee 100644 (file)
--- a/arch/x86/include/asm/pgtable-2level.h
+++ b/arch/x86/include/asm/pgtable-2level.h
@@ -19,9 +19,6 @@ static inline void native_set_pte(pte_t *ptep , pte_t pte)
 
 static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd)
 {
-#ifdef CONFIG_PAGE_TABLE_ISOLATION
-       pmd.pud.p4d.pgd = pti_set_user_pgtbl(&pmdp->pud.p4d.pgd, pmd.pud.p4d.pgd);
-#endif
        *pmdp = pmd;
 }
 
@@ -61,9 +58,6 @@ static inline pte_t native_ptep_get_and_clear(pte_t *xp)
 #ifdef CONFIG_SMP
 static inline pmd_t native_pmdp_get_and_clear(pmd_t *xp)
 {
-#ifdef CONFIG_PAGE_TABLE_ISOLATION
-       pti_set_user_pgtbl(&xp->pud.p4d.pgd, __pgd(0));
-#endif
        return __pmd(xchg((pmdval_t *)xp, 0));
 }
 #else
@@ -73,9 +67,6 @@ static inline pmd_t native_pmdp_get_and_clear(pmd_t *xp)
 #ifdef CONFIG_SMP
 static inline pud_t native_pudp_get_and_clear(pud_t *xp)
 {
-#ifdef CONFIG_PAGE_TABLE_ISOLATION
-       pti_set_user_pgtbl(&xp->p4d.pgd, __pgd(0));
-#endif
        return __pud(xchg((pudval_t *)xp, 0));
 }
 #else

diff --git a/security/Kconfig b/security/Kconfig
index 27d8b2688f755e974c0b168befc6c625529c3c66..d9aa521b52063501fce79062e35324a3c9046ec0 100644 (file)
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -57,7 +57,7 @@ config SECURITY_NETWORK
 config PAGE_TABLE_ISOLATION
        bool "Remove the kernel mapping in user mode"
        default y
-       depends on X86 && !UML
+       depends on (X86_64 || X86_PAE) && !UML
        help
          This feature reduces the number of hardware side channels by
          ensuring that the majority of kernel addresses are not mapped