x86/mm: Consider effective protection attributes in W+X check

Using just the leaf page table entry flags would cause a false warning
in case _PAGE_RW is clear or _PAGE_NX is set in a higher level entry.
Hand through both the current entry's flags as well as the accumulated
effective value (the latter as pgprotval_t instead of pgprot_t, as it's
not an actual entry's value).

This in particular eliminates the false W+X warning when running under
Xen, as commit:

  2cc42bac1c ("x86-64/Xen: eliminate W+X mappings")

had to make the necessary adjustment in L2 rather than L1 (the reason is
explained there). I.e. _PAGE_RW is clear there in L1, but _PAGE_NX is
set in L2.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
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: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/5A8FDE8902000078001AABBB@prv-mh.provo.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/dump_pagetables.c

@@ -29,6 +29,7 @@
 struct pg_state {
 	int level;
 	pgprot_t current_prot;
+	pgprotval_t effective_prot;
 	unsigned long start_address;
 	unsigned long current_address;
 	const struct addr_marker *marker;
@@ -235,9 +236,9 @@ static unsigned long normalize_addr(unsigned long u)
  * print what we collected so far.
  */
 static void note_page(struct seq_file *m, struct pg_state *st,
-		      pgprot_t new_prot, int level)
+		      pgprot_t new_prot, pgprotval_t new_eff, int level)
 {
-	pgprotval_t prot, cur;
+	pgprotval_t prot, cur, eff;
 	static const char units[] = "BKMGTPE";
 
 	/*
@@ -247,23 +248,24 @@ static void note_page(struct seq_file *m, struct pg_state *st,
 	 */
 	prot = pgprot_val(new_prot);
 	cur = pgprot_val(st->current_prot);
+	eff = st->effective_prot;
 
 	if (!st->level) {
 		/* First entry */
 		st->current_prot = new_prot;
+		st->effective_prot = new_eff;
 		st->level = level;
 		st->marker = address_markers;
 		st->lines = 0;
 		pt_dump_seq_printf(m, st->to_dmesg, "---[ %s ]---\n",
 				   st->marker->name);
-	} else if (prot != cur || level != st->level ||
+	} else if (prot != cur || new_eff != eff || level != st->level ||
 		   st->current_address >= st->marker[1].start_address) {
 		const char *unit = units;
 		unsigned long delta;
 		int width = sizeof(unsigned long) * 2;
-		pgprotval_t pr = pgprot_val(st->current_prot);
 
-		if (st->check_wx && (pr & _PAGE_RW) && !(pr & _PAGE_NX)) {
+		if (st->check_wx && (eff & _PAGE_RW) && !(eff & _PAGE_NX)) {
 			WARN_ONCE(1,
 				  "x86/mm: Found insecure W+X mapping at address %p/%pS\n",
 				  (void *)st->start_address,
@@ -317,21 +319,30 @@ static void note_page(struct seq_file *m, struct pg_state *st,
 
 		st->start_address = st->current_address;
 		st->current_prot = new_prot;
+		st->effective_prot = new_eff;
 		st->level = level;
 	}
 }
 
-static void walk_pte_level(struct seq_file *m, struct pg_state *st, pmd_t addr, unsigned long P)
+static inline pgprotval_t effective_prot(pgprotval_t prot1, pgprotval_t prot2)
+{
+	return (prot1 & prot2 & (_PAGE_USER | _PAGE_RW)) |
+	       ((prot1 | prot2) & _PAGE_NX);
+}
+
+static void walk_pte_level(struct seq_file *m, struct pg_state *st, pmd_t addr,
+			   pgprotval_t eff_in, unsigned long P)
 {
 	int i;
 	pte_t *start;
-	pgprotval_t prot;
+	pgprotval_t prot, eff;
 
 	start = (pte_t *)pmd_page_vaddr(addr);
 	for (i = 0; i < PTRS_PER_PTE; i++) {
 		prot = pte_flags(*start);
+		eff = effective_prot(eff_in, prot);
 		st->current_address = normalize_addr(P + i * PTE_LEVEL_MULT);
-		note_page(m, st, __pgprot(prot), 5);
+		note_page(m, st, __pgprot(prot), eff, 5);
 		start++;
 	}
 }
@@ -351,7 +362,7 @@ static inline bool kasan_page_table(struct seq_file *m, struct pg_state *st,
 	    (pgtable_l5_enabled && __pa(pt) == __pa(kasan_zero_p4d)) ||
 	    __pa(pt) == __pa(kasan_zero_pud)) {
 		pgprotval_t prot = pte_flags(kasan_zero_pte[0]);
-		note_page(m, st, __pgprot(prot), 5);
+		note_page(m, st, __pgprot(prot), 0, 5);
 		return true;
 	}
 	return false;
@@ -366,42 +377,45 @@ static inline bool kasan_page_table(struct seq_file *m, struct pg_state *st,
 
 #if PTRS_PER_PMD > 1
 
-static void walk_pmd_level(struct seq_file *m, struct pg_state *st, pud_t addr, unsigned long P)
+static void walk_pmd_level(struct seq_file *m, struct pg_state *st, pud_t addr,
+			   pgprotval_t eff_in, unsigned long P)
 {
 	int i;
 	pmd_t *start, *pmd_start;
-	pgprotval_t prot;
+	pgprotval_t prot, eff;
 
 	pmd_start = start = (pmd_t *)pud_page_vaddr(addr);
 	for (i = 0; i < PTRS_PER_PMD; i++) {
 		st->current_address = normalize_addr(P + i * PMD_LEVEL_MULT);
 		if (!pmd_none(*start)) {
+			prot = pmd_flags(*start);
+			eff = effective_prot(eff_in, prot);
 			if (pmd_large(*start) || !pmd_present(*start)) {
-				prot = pmd_flags(*start);
-				note_page(m, st, __pgprot(prot), 4);
+				note_page(m, st, __pgprot(prot), eff, 4);
 			} else if (!kasan_page_table(m, st, pmd_start)) {
-				walk_pte_level(m, st, *start,
+				walk_pte_level(m, st, *start, eff,
 					       P + i * PMD_LEVEL_MULT);
 			}
 		} else
-			note_page(m, st, __pgprot(0), 4);
+			note_page(m, st, __pgprot(0), 0, 4);
 		start++;
 	}
 }
 
 #else
-#define walk_pmd_level(m,s,a,p) walk_pte_level(m,s,__pmd(pud_val(a)),p)
+#define walk_pmd_level(m,s,a,e,p) walk_pte_level(m,s,__pmd(pud_val(a)),e,p)
 #define pud_large(a) pmd_large(__pmd(pud_val(a)))
 #define pud_none(a)  pmd_none(__pmd(pud_val(a)))
 #endif
 
 #if PTRS_PER_PUD > 1
 
-static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr, unsigned long P)
+static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr,
+			   pgprotval_t eff_in, unsigned long P)
 {
 	int i;
 	pud_t *start, *pud_start;
-	pgprotval_t prot;
+	pgprotval_t prot, eff;
 	pud_t *prev_pud = NULL;
 
 	pud_start = start = (pud_t *)p4d_page_vaddr(addr);
@@ -409,15 +423,16 @@ static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr,
 	for (i = 0; i < PTRS_PER_PUD; i++) {
 		st->current_address = normalize_addr(P + i * PUD_LEVEL_MULT);
 		if (!pud_none(*start)) {
+			prot = pud_flags(*start);
+			eff = effective_prot(eff_in, prot);
 			if (pud_large(*start) || !pud_present(*start)) {
-				prot = pud_flags(*start);
-				note_page(m, st, __pgprot(prot), 3);
+				note_page(m, st, __pgprot(prot), eff, 3);
 			} else if (!kasan_page_table(m, st, pud_start)) {
-				walk_pmd_level(m, st, *start,
+				walk_pmd_level(m, st, *start, eff,
 					       P + i * PUD_LEVEL_MULT);
 			}
 		} else
-			note_page(m, st, __pgprot(0), 3);
+			note_page(m, st, __pgprot(0), 0, 3);
 
 		prev_pud = start;
 		start++;
@@ -425,34 +440,36 @@ static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr,
 }
 
 #else
-#define walk_pud_level(m,s,a,p) walk_pmd_level(m,s,__pud(p4d_val(a)),p)
+#define walk_pud_level(m,s,a,e,p) walk_pmd_level(m,s,__pud(p4d_val(a)),e,p)
 #define p4d_large(a) pud_large(__pud(p4d_val(a)))
 #define p4d_none(a)  pud_none(__pud(p4d_val(a)))
 #endif
 
-static void walk_p4d_level(struct seq_file *m, struct pg_state *st, pgd_t addr, unsigned long P)
+static void walk_p4d_level(struct seq_file *m, struct pg_state *st, pgd_t addr,
+			   pgprotval_t eff_in, unsigned long P)
 {
 	int i;
 	p4d_t *start, *p4d_start;
-	pgprotval_t prot;
+	pgprotval_t prot, eff;
 
 	if (PTRS_PER_P4D == 1)
-		return walk_pud_level(m, st, __p4d(pgd_val(addr)), P);
+		return walk_pud_level(m, st, __p4d(pgd_val(addr)), eff_in, P);
 
 	p4d_start = start = (p4d_t *)pgd_page_vaddr(addr);
 
 	for (i = 0; i < PTRS_PER_P4D; i++) {
 		st->current_address = normalize_addr(P + i * P4D_LEVEL_MULT);
 		if (!p4d_none(*start)) {
+			prot = p4d_flags(*start);
+			eff = effective_prot(eff_in, prot);
 			if (p4d_large(*start) || !p4d_present(*start)) {
-				prot = p4d_flags(*start);
-				note_page(m, st, __pgprot(prot), 2);
+				note_page(m, st, __pgprot(prot), eff, 2);
 			} else if (!kasan_page_table(m, st, p4d_start)) {
-				walk_pud_level(m, st, *start,
+				walk_pud_level(m, st, *start, eff,
 					       P + i * P4D_LEVEL_MULT);
 			}
 		} else
-			note_page(m, st, __pgprot(0), 2);
+			note_page(m, st, __pgprot(0), 0, 2);
 
 		start++;
 	}
@@ -483,7 +500,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 #else
 	pgd_t *start = swapper_pg_dir;
 #endif
-	pgprotval_t prot;
+	pgprotval_t prot, eff;
 	int i;
 	struct pg_state st = {};
 
@@ -499,15 +516,20 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 	for (i = 0; i < PTRS_PER_PGD; i++) {
 		st.current_address = normalize_addr(i * PGD_LEVEL_MULT);
 		if (!pgd_none(*start) && !is_hypervisor_range(i)) {
+			prot = pgd_flags(*start);
+#ifdef CONFIG_X86_PAE
+			eff = _PAGE_USER | _PAGE_RW;
+#else
+			eff = prot;
+#endif
 			if (pgd_large(*start) || !pgd_present(*start)) {
-				prot = pgd_flags(*start);
-				note_page(m, &st, __pgprot(prot), 1);
+				note_page(m, &st, __pgprot(prot), eff, 1);
 			} else {
-				walk_p4d_level(m, &st, *start,
+				walk_p4d_level(m, &st, *start, eff,
 					       i * PGD_LEVEL_MULT);
 			}
 		} else
-			note_page(m, &st, __pgprot(0), 1);
+			note_page(m, &st, __pgprot(0), 0, 1);
 
 		cond_resched();
 		start++;
@@ -515,7 +537,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 
 	/* Flush out the last page */
 	st.current_address = normalize_addr(PTRS_PER_PGD*PGD_LEVEL_MULT);
-	note_page(m, &st, __pgprot(0), 0);
+	note_page(m, &st, __pgprot(0), 0, 0);
 	if (!checkwx)
 		return;
 	if (st.wx_pages)