Commit 61a6bd83 authored Sep 14, 2018 by Joerg Roedel Committed by Thomas Gleixner Sep 14, 2018

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



This reverts commit 1f40a46c.

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: 7757d607 ('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

parent cf40361e

arch/x86/include/asm/pgtable-2level.h

+0 −9

Original line number	Diff line number	Diff line
		@@ -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

security/Kconfig

+1 −1

Original line number	Diff line number	Diff line
		@@ -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

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