[RFC][PATCH 05/10] x86/mm: do not auto-massage page protections

[Dave Hansen <dave.hansen@linux.intel.com>]

From: Dave Hansen <dave.hansen@linux.intel.com>

A PTE is constructed from a physical address and a pgprotval_t.
__PAGE_KERNEL, for instance, is a pgprot_t and must be converted
into a pgprotval_t before it can be used to create a PTE.  This is
done implicitly within functions like set_pte() by massage_pgprot().

However, this makes it very challenging to set bits (and keep them
set) if your bit is being filtered out by massage_pgprot().

This moves the bit filtering out of set_pte() and friends.  For
users of PAGE_KERNEL*, filtering will be done automatically inside
those macros but for users of __PAGE_KERNEL*, they need to do their
own filtering now.

Note that we also just move pfn_pte/pmd/pud() over to check_pgprot()
instead of massage_pgprot().  This way, we still *look* for
unsupported bits and properly warn about them if we find them.  This
might happen if an unfiltered __PAGE_KERNEL* value was passed in,
for instance.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: x86@kernel.org
Cc: Nadav Amit <namit@vmware.com>
---

 b/arch/x86/include/asm/pgtable.h |   24 +++++++++++++++++++-----
 b/arch/x86/kernel/head64.c       |    2 ++
 b/arch/x86/kernel/ldt.c          |    6 +++++-
 b/arch/x86/mm/ident_map.c        |    3 +++
 b/arch/x86/mm/iomap_32.c         |    6 ++++++
 b/arch/x86/mm/kasan_init_64.c    |   14 +++++++++++++-
 b/arch/x86/power/hibernate_64.c  |   20 +++++++++++++++-----
 b/mm/early_ioremap.c             |    3 +++
 8 files changed, 66 insertions(+), 12 deletions(-)

diff -puN arch/x86/include/asm/pgtable.h~x86-no-auto-massage arch/x86/include/asm/pgtable.h
--- a/arch/x86/include/asm/pgtable.h~x86-no-auto-massage	2018-02-22 12:36:19.752036551 -0800
+++ b/arch/x86/include/asm/pgtable.h	2018-02-22 12:36:19.769036551 -0800
@@ -526,22 +526,36 @@ static inline pgprotval_t massage_pgprot
 	return protval;
 }
 
+static inline pgprotval_t check_pgprot(pgprot_t pgprot)
+{
+	pgprotval_t massaged_val = massage_pgprot(pgprot);
+
+	WARN_ONCE(pgprot_val(pgprot) != massaged_val,
+		  "attempted to set unsupported pgprot: %016lx "
+		  "bits: %016lx supported: %016lx\n",
+		  pgprot_val(pgprot),
+		  pgprot_val(pgprot) ^ massaged_val,
+		  __supported_pte_mask);
+
+	return massaged_val;
+}
+
 static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot)
 {
 	return __pte(((phys_addr_t)page_nr << PAGE_SHIFT) |
-		     massage_pgprot(pgprot));
+		     check_pgprot(pgprot));
 }
 
 static inline pmd_t pfn_pmd(unsigned long page_nr, pgprot_t pgprot)
 {
 	return __pmd(((phys_addr_t)page_nr << PAGE_SHIFT) |
-		     massage_pgprot(pgprot));
+		     check_pgprot(pgprot));
 }
 
 static inline pud_t pfn_pud(unsigned long page_nr, pgprot_t pgprot)
 {
 	return __pud(((phys_addr_t)page_nr << PAGE_SHIFT) |
-		     massage_pgprot(pgprot));
+		     check_pgprot(pgprot));
 }
 
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
@@ -553,7 +567,7 @@ static inline pte_t pte_modify(pte_t pte
 	 * the newprot (if present):
 	 */
 	val &= _PAGE_CHG_MASK;
-	val |= massage_pgprot(newprot) & ~_PAGE_CHG_MASK;
+	val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
 
 	return __pte(val);
 }
@@ -563,7 +577,7 @@ static inline pmd_t pmd_modify(pmd_t pmd
 	pmdval_t val = pmd_val(pmd);
 
 	val &= _HPAGE_CHG_MASK;
-	val |= massage_pgprot(newprot) & ~_HPAGE_CHG_MASK;
+	val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
 
 	return __pmd(val);
 }
diff -puN arch/x86/kernel/head64.c~x86-no-auto-massage arch/x86/kernel/head64.c
--- a/arch/x86/kernel/head64.c~x86-no-auto-massage	2018-02-22 12:36:19.754036551 -0800
+++ b/arch/x86/kernel/head64.c	2018-02-22 12:36:19.769036551 -0800
@@ -129,6 +129,8 @@ unsigned long __head __startup_64(unsign
 	pud[i + 1] = (pudval_t)pmd + pgtable_flags;
 
 	pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL;
+	/* Filter out unsupported __PAGE_KERNEL_* bits: */
+	pmd_entry |= __supported_pte_mask;
 	pmd_entry += sme_get_me_mask();
 	pmd_entry +=  physaddr;
 
diff -puN arch/x86/kernel/ldt.c~x86-no-auto-massage arch/x86/kernel/ldt.c
--- a/arch/x86/kernel/ldt.c~x86-no-auto-massage	2018-02-22 12:36:19.756036551 -0800
+++ b/arch/x86/kernel/ldt.c	2018-02-22 12:36:19.769036551 -0800
@@ -145,6 +145,7 @@ map_ldt_struct(struct mm_struct *mm, str
 		unsigned long offset = i << PAGE_SHIFT;
 		const void *src = (char *)ldt->entries + offset;
 		unsigned long pfn;
+		pgprot_t pte_prot;
 		pte_t pte, *ptep;
 
 		va = (unsigned long)ldt_slot_va(slot) + offset;
@@ -163,7 +164,10 @@ map_ldt_struct(struct mm_struct *mm, str
 		 * target via some kernel interface which misses a
 		 * permission check.
 		 */
-		pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL));
+	       	pte_prot = __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL);
+		/* Filter out unsuppored __PAGE_KERNEL* bits: */
+		pgprot_val(pte_prot) |= __supported_pte_mask;
+		pte = pfn_pte(pfn, pte_prot);
 		set_pte_at(mm, va, ptep, pte);
 		pte_unmap_unlock(ptep, ptl);
 	}
diff -puN arch/x86/mm/ident_map.c~x86-no-auto-massage arch/x86/mm/ident_map.c
--- a/arch/x86/mm/ident_map.c~x86-no-auto-massage	2018-02-22 12:36:19.758036551 -0800
+++ b/arch/x86/mm/ident_map.c	2018-02-22 12:36:19.769036551 -0800
@@ -98,6 +98,9 @@ int kernel_ident_mapping_init(struct x86
 	if (!info->kernpg_flag)
 		info->kernpg_flag = _KERNPG_TABLE;
 
+	/* Filter out unsupported __PAGE_KERNEL_* bits: */
+	info->kernpg_flag &= __default_kernel_pte_mask;
+
 	for (; addr < end; addr = next) {
 		pgd_t *pgd = pgd_page + pgd_index(addr);
 		p4d_t *p4d;
diff -puN arch/x86/mm/iomap_32.c~x86-no-auto-massage arch/x86/mm/iomap_32.c
--- a/arch/x86/mm/iomap_32.c~x86-no-auto-massage	2018-02-22 12:36:19.760036551 -0800
+++ b/arch/x86/mm/iomap_32.c	2018-02-22 12:36:19.770036551 -0800
@@ -44,6 +44,9 @@ int iomap_create_wc(resource_size_t base
 		return ret;
 
 	*prot = __pgprot(__PAGE_KERNEL | cachemode2protval(pcm));
+	/* Filter out unsupported __PAGE_KERNEL* bits: */
+	pgprot_val(*prot) &= __default_kernel_pte_mask;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(iomap_create_wc);
@@ -88,6 +91,9 @@ iomap_atomic_prot_pfn(unsigned long pfn,
 		prot = __pgprot(__PAGE_KERNEL |
 				cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS));
 
+	/* Filter out unsupported __PAGE_KERNEL* bits: */
+	pgprot_val(prot) &= __default_kernel_pte_mask;
+
 	return (void __force __iomem *) kmap_atomic_prot_pfn(pfn, prot);
 }
 EXPORT_SYMBOL_GPL(iomap_atomic_prot_pfn);
diff -puN arch/x86/mm/kasan_init_64.c~x86-no-auto-massage arch/x86/mm/kasan_init_64.c
--- a/arch/x86/mm/kasan_init_64.c~x86-no-auto-massage	2018-02-22 12:36:19.761036551 -0800
+++ b/arch/x86/mm/kasan_init_64.c	2018-02-22 12:36:19.770036551 -0800
@@ -263,6 +263,12 @@ void __init kasan_early_init(void)
 	pudval_t pud_val = __pa_nodebug(kasan_zero_pmd) | _KERNPG_TABLE;
 	p4dval_t p4d_val = __pa_nodebug(kasan_zero_pud) | _KERNPG_TABLE;
 
+	/* Mask out unsupported __PAGE_KERNEL bits: */
+	pte_val &= __default_kernel_pte_mask;
+	pmd_val &= __default_kernel_pte_mask;
+	pud_val &= __default_kernel_pte_mask;
+	p4d_val &= __default_kernel_pte_mask;
+
 	for (i = 0; i < PTRS_PER_PTE; i++)
 		kasan_zero_pte[i] = __pte(pte_val);
 
@@ -365,7 +371,13 @@ void __init kasan_init(void)
 	 */
 	memset(kasan_zero_page, 0, PAGE_SIZE);
 	for (i = 0; i < PTRS_PER_PTE; i++) {
-		pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO | _PAGE_ENC);
+		pte_t pte;
+		pgprot_t prot;
+
+		prot = __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC);
+		pgprot_val(prot) &= __default_kernel_pte_mask;
+
+		pte = __pte(__pa(kasan_zero_page) | pgprot_val(prot));
 		set_pte(&kasan_zero_pte[i], pte);
 	}
 	/* Flush TLBs again to be sure that write protection applied. */
diff -puN arch/x86/power/hibernate_64.c~x86-no-auto-massage arch/x86/power/hibernate_64.c
--- a/arch/x86/power/hibernate_64.c~x86-no-auto-massage	2018-02-22 12:36:19.763036551 -0800
+++ b/arch/x86/power/hibernate_64.c	2018-02-22 12:36:19.770036551 -0800
@@ -51,6 +51,12 @@ static int set_up_temporary_text_mapping
 	pmd_t *pmd;
 	pud_t *pud;
 	p4d_t *p4d;
+	pgprot_t pgtable_prot = __pgprot(_KERNPG_TABLE);
+	pgprot_t pmd_text_prot = __pgprot(__PAGE_KERNEL_LARGE_EXEC);
+
+	/* Filter out unsupported __PAGE_KERNEL* bits: */
+	pgprot_val(pmd_text_prot) &= __default_kernel_pte_mask;
+	pgprot_val(pgtable_prot)  &= __default_kernel_pte_mask;
 
 	/*
 	 * The new mapping only has to cover the page containing the image
@@ -81,15 +87,19 @@ static int set_up_temporary_text_mapping
 		return -ENOMEM;
 
 	set_pmd(pmd + pmd_index(restore_jump_address),
-		__pmd((jump_address_phys & PMD_MASK) | __PAGE_KERNEL_LARGE_EXEC));
+		__pmd((jump_address_phys & PMD_MASK) | pgprot_val(pmd_text_prot)));
 	set_pud(pud + pud_index(restore_jump_address),
-		__pud(__pa(pmd) | _KERNPG_TABLE));
+		__pud(__pa(pmd) | pgprot_val(pgtable_prot)));
 	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
-		set_p4d(p4d + p4d_index(restore_jump_address), __p4d(__pa(pud) | _KERNPG_TABLE));
-		set_pgd(pgd + pgd_index(restore_jump_address), __pgd(__pa(p4d) | _KERNPG_TABLE));
+		p4d_t new_p4d = __p4d(__pa(pud) | pgprot_val(pgtable_prot));
+		pgd_t new_pgd = __pgd(__pa(p4d) | pgprot_val(pgtable_prot));
+
+		set_p4d(p4d + p4d_index(restore_jump_address), new_p4d);
+		set_pgd(pgd + pgd_index(restore_jump_address), new_pgd);
 	} else {
 		/* No p4d for 4-level paging: point the pgd to the pud page table */
-		set_pgd(pgd + pgd_index(restore_jump_address), __pgd(__pa(pud) | _KERNPG_TABLE));
+		pgd_t new_pgd = __pgd(__pa(p4d) | pgprot_val(pgtable_prot));
+		set_pgd(pgd + pgd_index(restore_jump_address), new_pgd);
 	}
 
 	return 0;
diff -puN mm/early_ioremap.c~x86-no-auto-massage mm/early_ioremap.c
--- a/mm/early_ioremap.c~x86-no-auto-massage	2018-02-22 12:36:19.765036551 -0800
+++ b/mm/early_ioremap.c	2018-02-22 12:36:19.770036551 -0800
@@ -113,6 +113,9 @@ __early_ioremap(resource_size_t phys_add
 
 	WARN_ON(system_state >= SYSTEM_RUNNING);
 
+	/* Sanitize 'prot' against any unsupported bits: */
+	pgprot_val(prot) &= __default_kernel_pte_mask;
+
 	slot = -1;
 	for (i = 0; i < FIX_BTMAPS_SLOTS; i++) {
 		if (!prev_map[i]) {
_