x86: mm: ptdump: calculate effective permissions correctly

Patch series "Fix W+X debug feature on x86"

Jan alerted me[1] that the W+X detection debug feature was broken in x86
by my change[2] to switch x86 to use the generic ptdump infrastructure.

Fundamentally the approach of trying to move the calculation of
effective permissions into note_page() was broken because note_page() is
only called for 'leaf' entries and the effective permissions are passed
down via the internal nodes of the page tree.  The solution I've taken
here is to create a new (optional) callback which is called for all
nodes of the page tree and therefore can calculate the effective
permissions.

Secondly on some configurations (32 bit with PAE) "unsigned long" is not
large enough to store the table entries.  The fix here is simple - let's
just use a u64.

[1] https://lore.kernel.org/lkml/d573dc7e-e742-84de-473d-f971142fa319@suse.com/
[2] 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range")

This patch (of 2):

By switching the x86 page table dump code to use the generic code the
effective permissions are no longer calculated correctly because the
note_page() function is only called for *leaf* entries.  To calculate
the actual effective permissions it is necessary to observe the full
hierarchy of the page tree.

Introduce a new callback for ptdump which is called for every entry and
can therefore update the prot_levels array correctly.  note_page() can
then simply access the appropriate element in the array.

[steven.price@arm.com: make the assignment conditional on val != 0]
  Link: http://lkml.kernel.org/r/430c8ab4-e7cd-6933-dde6-087fac6db872@arm.com
Fixes: 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range")
Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Qian Cai <cai@lca.pw>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200521152308.33096-1-steven.price@arm.com
Link: http://lkml.kernel.org/r/20200521152308.33096-2-steven.price@arm.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/mm/ptdump.c b/mm/ptdump.c
index 26208d0d03b7..f4ce916f5602 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -36,6 +36,9 @@ static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr,
 		return note_kasan_page_table(walk, addr);
 #endif
 
+	if (st->effective_prot)
+		st->effective_prot(st, 0, pgd_val(val));
+
 	if (pgd_leaf(val))
 		st->note_page(st, addr, 0, pgd_val(val));
 
@@ -53,6 +56,9 @@ static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr,
 		return note_kasan_page_table(walk, addr);
 #endif
 
+	if (st->effective_prot)
+		st->effective_prot(st, 1, p4d_val(val));
+
 	if (p4d_leaf(val))
 		st->note_page(st, addr, 1, p4d_val(val));
 
@@ -70,6 +76,9 @@ static int ptdump_pud_entry(pud_t *pud, unsigned long addr,
 		return note_kasan_page_table(walk, addr);
 #endif
 
+	if (st->effective_prot)
+		st->effective_prot(st, 2, pud_val(val));
+
 	if (pud_leaf(val))
 		st->note_page(st, addr, 2, pud_val(val));
 
@@ -87,6 +96,8 @@ static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr,
 		return note_kasan_page_table(walk, addr);
 #endif
 
+	if (st->effective_prot)
+		st->effective_prot(st, 3, pmd_val(val));
 	if (pmd_leaf(val))
 		st->note_page(st, addr, 3, pmd_val(val));
 
@@ -97,8 +108,12 @@ static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
 			    unsigned long next, struct mm_walk *walk)
 {
 	struct ptdump_state *st = walk->private;
+	pte_t val = READ_ONCE(*pte);
+
+	if (st->effective_prot)
+		st->effective_prot(st, 4, pte_val(val));
 
-	st->note_page(st, addr, 4, pte_val(READ_ONCE(*pte)));
+	st->note_page(st, addr, 4, pte_val(val));
 
 	return 0;
 }