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

  2cc42ba ("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>
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Jan Beulich authored and Ingo Molnar committed Feb 26, 2018
1 parent c46dacb commit 672c0ae
Showing 1 changed file with 58 additions and 36 deletions.
94 changes: 58 additions & 36 deletions arch/x86/mm/dump_pagetables.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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";

/*
Expand All @@ -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,
Expand Down Expand Up @@ -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++;
}
}
Expand All @@ -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;
Expand All @@ -366,93 +377,99 @@ 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);

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++;
}
}

#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++;
}
Expand Down Expand Up @@ -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 = {};

Expand All @@ -499,23 +516,28 @@ 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++;
}

/* 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)
Expand Down

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