[PATCH v2] x86: consider effective protection attributes in W+X check

[PATCH v2] x86: consider effective protection attributes in W+X check

[Jan Beulich]

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") has 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>
---
v2: Re-base onto tip tree. Add Xen related paragraph to description.
---
 arch/x86/mm/dump_pagetables.c |   92 ++++++++++++++++++++++++++----------------
 1 file changed, 57 insertions(+), 35 deletions(-)

--- 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(unsi
  * 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
 	 */
 	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
 
 		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++;
 	}
 }
@@ -366,42 +377,45 @@ static inline bool kasan_page_table(stru
 
 #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_fi
 	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_fi
 }
 
 #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(s
 #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(s
 	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(s
 
 	/* 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)

Re: [PATCH v2] x86: consider effective protection attributes in W+X check

[Ingo Molnar]

* Jan Beulich <JBeulich@suse.com> wrote:

> 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") has 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>
> ---
> v2: Re-base onto tip tree. Add Xen related paragraph to description.
> ---
>  arch/x86/mm/dump_pagetables.c |   92 ++++++++++++++++++++++++++----------------
>  1 file changed, 57 insertions(+), 35 deletions(-)

There's a build failure with CONFIG_KASAN=y enabled:

 arch/x86/mm/dump_pagetables.c: In function ‘kasan_page_table’:
 arch/x86/mm/dump_pagetables.c:365:3: error: too few arguments to function ‘note_page’
 arch/x86/mm/dump_pagetables.c:238:13: note: declared here

Thanks,

	Ingo

Re: [PATCH v2] x86: consider effective protection attributes in W+X check

[Jan Beulich]

>>> On 21.02.18 at 17:53, <mingo@kernel.org> wrote:

> * Jan Beulich <JBeulich@suse.com> wrote:
> 
>> 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") has 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>
>> ---
>> v2: Re-base onto tip tree. Add Xen related paragraph to description.
>> ---
>>  arch/x86/mm/dump_pagetables.c |   92 
> ++++++++++++++++++++++++++----------------
>>  1 file changed, 57 insertions(+), 35 deletions(-)
> 
> There's a build failure with CONFIG_KASAN=y enabled:
> 
>  arch/x86/mm/dump_pagetables.c: In function ‘kasan_page_table’:
>  arch/x86/mm/dump_pagetables.c:365:3: error: too few arguments to function ‘note_page’
>  arch/x86/mm/dump_pagetables.c:238:13: note: declared here

Oh, I see. Question though is what to pass as the extra argument:
Do I need to pass in the caller's effective rights, or should I take
kasan_page_table()'s checking against kasan_zero_p?d as an
indication that the effective permission is zero here? I'm sorry for
this probably trivial question, but I know nothing about how KASAN
works.

Jan

Re: [PATCH v2] x86: consider effective protection attributes in W+X check

[Ingo Molnar]

* Jan Beulich <JBeulich@suse.com> wrote:

> >>> On 21.02.18 at 17:53, <mingo@kernel.org> wrote:
> 
> > * Jan Beulich <JBeulich@suse.com> wrote:
> > 
> >> 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") has 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>
> >> ---
> >> v2: Re-base onto tip tree. Add Xen related paragraph to description.
> >> ---
> >>  arch/x86/mm/dump_pagetables.c |   92 
> > ++++++++++++++++++++++++++----------------
> >>  1 file changed, 57 insertions(+), 35 deletions(-)
> > 
> > There's a build failure with CONFIG_KASAN=y enabled:
> > 
> >  arch/x86/mm/dump_pagetables.c: In function ‘kasan_page_table’:
> >  arch/x86/mm/dump_pagetables.c:365:3: error: too few arguments to function ‘note_page’
> >  arch/x86/mm/dump_pagetables.c:238:13: note: declared here
> 
> Oh, I see. Question though is what to pass as the extra argument:
> Do I need to pass in the caller's effective rights, or should I take
> kasan_page_table()'s checking against kasan_zero_p?d as an
> indication that the effective permission is zero here? I'm sorry for
> this probably trivial question, but I know nothing about how KASAN
> works.

I'm not sure either - but I've Cc:-ed the KASAN gents who might be able to
help us out here?

Thanks,

	Ingo

Re: [PATCH v2] x86: consider effective protection attributes in W+X check

[Jan Beulich]

>>> On 23.02.18 at 08:49, <mingo@kernel.org> wrote:

> * Jan Beulich <JBeulich@suse.com> wrote:
> 
>> >>> On 21.02.18 at 17:53, <mingo@kernel.org> wrote:
>> 
>> > * Jan Beulich <JBeulich@suse.com> wrote:
>> > 
>> >> 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") has 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>
>> >> ---
>> >> v2: Re-base onto tip tree. Add Xen related paragraph to description.
>> >> ---
>> >>  arch/x86/mm/dump_pagetables.c |   92 
>> > ++++++++++++++++++++++++++----------------
>> >>  1 file changed, 57 insertions(+), 35 deletions(-)
>> > 
>> > There's a build failure with CONFIG_KASAN=y enabled:
>> > 
>> >  arch/x86/mm/dump_pagetables.c: In function ‘kasan_page_table’:
>> >  arch/x86/mm/dump_pagetables.c:365:3: error: too few arguments to function ‘note_page’
>> >  arch/x86/mm/dump_pagetables.c:238:13: note: declared here
>> 
>> Oh, I see. Question though is what to pass as the extra argument:
>> Do I need to pass in the caller's effective rights, or should I take
>> kasan_page_table()'s checking against kasan_zero_p?d as an
>> indication that the effective permission is zero here? I'm sorry for
>> this probably trivial question, but I know nothing about how KASAN
>> works.
> 
> I'm not sure either - but I've Cc:-ed the KASAN gents who might be able to
> help us out here?

Actually, the "zero" in the names of the symbols meanwhile makes
me be pretty sure passing 0 for the effective permissions here is
exactly what is wanted. I'm about to produce v3.

Jan

[PATCH v3] x86: consider effective protection attributes in W+X check

[Jan Beulich]

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") has 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>
---
v3: Fix build issue with CONFIG_KASAN.
v2: Re-base onto tip tree. Add Xen related paragraph to description.
---
 arch/x86/mm/dump_pagetables.c |   94 +++++++++++++++++++++++++-----------------
 1 file changed, 58 insertions(+), 36 deletions(-)

--- 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(unsi
  * 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
 	 */
 	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
 
 		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(stru
 	    (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(stru
 
 #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_fi
 	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_fi
 }
 
 #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(s
 #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(s
 	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(s
 
 	/* 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)

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

[tip-bot for Jan Beulich]

Commit-ID:  6e558c9d10146ebe7f04917af2f8533b811f9c25
Gitweb:     https://git.kernel.org/tip/6e558c9d10146ebe7f04917af2f8533b811f9c25
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Fri, 23 Feb 2018 01:27:37 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 23 Feb 2018 09:51:38 +0100

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 | 94 ++++++++++++++++++++++++++-----------------
 1 file changed, 58 insertions(+), 36 deletions(-)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 0d6d67d18ad6..62a7e9f65dec 100644
--- 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)

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

[tip-bot for Jan Beulich]

Commit-ID:  672c0ae09b33a11d8f31fc61526632e96301164c
Gitweb:     https://git.kernel.org/tip/672c0ae09b33a11d8f31fc61526632e96301164c
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Fri, 23 Feb 2018 01:27:37 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 26 Feb 2018 08:43:21 +0100

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 | 94 ++++++++++++++++++++++++++-----------------
 1 file changed, 58 insertions(+), 36 deletions(-)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 0d6d67d18ad6..62a7e9f65dec 100644
--- 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)

Re: [tip:x86/mm] x86/mm: Consider effective protection attributes in W+X check

[Andrey Ryabinin]

On 02/26/2018 11:48 AM, tip-bot for Jan Beulich wrote:

>  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);

Isn't this disables W+X check for kasan page table?
Methinks it should be 'prot' here.

Re: [tip:x86/mm] x86/mm: Consider effective protection attributes in W+X check

[Jan Beulich]

>>> On 26.02.18 at 11:00, <aryabinin@virtuozzo.com> wrote:
> On 02/26/2018 11:48 AM, tip-bot for Jan Beulich wrote:
>> @@ -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);
> 
> Isn't this disables W+X check for kasan page table?
> Methinks it should be 'prot' here.

Might well be - I actually did ask the question before sending v3,
but didn't get any answer (yet). The kasan_zero_p?d names
suggested to me that this is a shortcut for mappings which
otherwise would be non-present anyway, but that was merely a
guess. As to W+X checks - I can't see how the result could be
any better if the protections of kasan_zero_pte[0] would be
used: Those can't possibly be applicable independent of VA.

Jan

Re: [tip:x86/mm] x86/mm: Consider effective protection attributes in W+X check

[Andrey Ryabinin]

On 02/26/2018 01:08 PM, Jan Beulich wrote:
>>>> On 26.02.18 at 11:00, <aryabinin@virtuozzo.com> wrote:
>> On 02/26/2018 11:48 AM, tip-bot for Jan Beulich wrote:
>>> @@ -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);
>>
>> Isn't this disables W+X check for kasan page table?
>> Methinks it should be 'prot' here.
> 
> Might well be - I actually did ask the question before sending v3,
> but didn't get any answer (yet). The kasan_zero_p?d names
> suggested to me that this is a shortcut for mappings which
> otherwise would be non-present anyway, but that was merely a
> guess. 

kasan_zero_p?? are used to map kasan_zero_page. That's it.

> As to W+X checks - I can't see how the result could be
> any better if the protections of kasan_zero_pte[0] would be
> used: Those can't possibly be applicable independent of VA.

I'm not sure I understand what do you mean.
If we somehow screw up and accidentally make kasan_zero_pte writable and executable,
note_page() should report this. With your patch, it won't work. 

Re: [tip:x86/mm] x86/mm: Consider effective protection attributes in W+X check

[Jan Beulich]

>>> On 26.02.18 at 11:47, <aryabinin@virtuozzo.com> wrote:

> 
> On 02/26/2018 01:08 PM, Jan Beulich wrote:
>>>>> On 26.02.18 at 11:00, <aryabinin@virtuozzo.com> wrote:
>>> On 02/26/2018 11:48 AM, tip-bot for Jan Beulich wrote:
>>>> @@ -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);
>>>
>>> Isn't this disables W+X check for kasan page table?
>>> Methinks it should be 'prot' here.
>> 
>> Might well be - I actually did ask the question before sending v3,
>> but didn't get any answer (yet). The kasan_zero_p?d names
>> suggested to me that this is a shortcut for mappings which
>> otherwise would be non-present anyway, but that was merely a
>> guess. 
> 
> kasan_zero_p?? are used to map kasan_zero_page. That's it.

Ah, thanks for explaining.

>> As to W+X checks - I can't see how the result could be
>> any better if the protections of kasan_zero_pte[0] would be
>> used: Those can't possibly be applicable independent of VA.
> 
> I'm not sure I understand what do you mean.
> If we somehow screw up and accidentally make kasan_zero_pte writable and executable,
> note_page() should report this. With your patch, it won't work. 

If this is a case to care about, simply passing "prot" won't be right
though - the callers accumulated effective protections would then
need passing in here, and merging with prot.

Before I do this for a possible v4, I'd like to seek clarification
though whether this really is a case to care about.

Jan

Re: [tip:x86/mm] x86/mm: Consider effective protection attributes in W+X check

[Andrey Ryabinin]

On 02/26/2018 01:54 PM, Jan Beulich wrote:
>>>> On 26.02.18 at 11:47, <aryabinin@virtuozzo.com> wrote:
> 
>>
>> On 02/26/2018 01:08 PM, Jan Beulich wrote:
>>>>>> On 26.02.18 at 11:00, <aryabinin@virtuozzo.com> wrote:
>>>> On 02/26/2018 11:48 AM, tip-bot for Jan Beulich wrote:
>>>>> @@ -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);
>>>>
>>>> Isn't this disables W+X check for kasan page table?
>>>> Methinks it should be 'prot' here.
>>>
>>> Might well be - I actually did ask the question before sending v3,
>>> but didn't get any answer (yet). The kasan_zero_p?d names
>>> suggested to me that this is a shortcut for mappings which
>>> otherwise would be non-present anyway, but that was merely a
>>> guess. 
>>
>> kasan_zero_p?? are used to map kasan_zero_page. That's it.
> 
> Ah, thanks for explaining.
> 
>>> As to W+X checks - I can't see how the result could be
>>> any better if the protections of kasan_zero_pte[0] would be
>>> used: Those can't possibly be applicable independent of VA.
>>
>> I'm not sure I understand what do you mean.
>> If we somehow screw up and accidentally make kasan_zero_pte writable and executable,
>> note_page() should report this. With your patch, it won't work. 
> 
> If this is a case to care about, simply passing "prot" won't be right
> though - the callers accumulated effective protections would then
> need passing in here, and merging with prot.
> 

Fine, but this won't change anything. Since kasan_zero_pte[] always ro+nx, the effective
protections should be always the same.

> Before I do this for a possible v4, I'd like to seek clarification
> though whether this really is a case to care about.

It may be not that important case, but one of the points of this code is to check for the absence
of W+X mappings. Passing known to be wrong value to bypass that check is certainly not the
right thing to do.


> Jan
>