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>

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 0d6d67d18ad6dd580bd60e7bfc5381cb6332383c..62a7e9f65decfcc5c447c01a9b5f986079f1de6f 100644 (file)
--- a/arch/x86/mm/dump_pagetables.c
+++ b/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)