[RFC][PATCH] x86/mm: warn on W+x mappings

Stephen Smalley
2015-10-01T16:32:01Z

Warn on any residual W+x mappings if X86_PTDUMP is enabled.

Sample dmesg output:
Checking for W+x mappings
0xffffffff81755000-0xffffffff81800000 684K RW GLB x pte
Found W+x mappings. Please fix.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
Not sure if this is the best place to put this check.
It must occur after free_init_pages() or it won't catch the
W+x case for the gap between __ex_table and rodata.

arch/x86/include/asm/pgtable.h | 6 ++++++
arch/x86/mm/dump_pagetables.c | 31 ++++++++++++++++++++++++++++++-
arch/x86/mm/init_64.c | 2 ++
3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 867da5b..8e771c1 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -20,6 +20,12 @@

void ptdump_walk_pgd_level(struct seq_file *m, pgd_t *pgd);

+#ifdef CONFIG_X86_PTDUMP
+void ptdump_walk_pgd_level_checkwx(void);
+#else
+#define ptdump_walk_pgd_level_checkwx() do { } while (0)
+#endif
+
/*
* ZERO_PAGE is a global shared page that is always zero: used
* for zero-mapped memory areas etc..
diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index f0cedf3..986903b 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -32,6 +32,8 @@ struct pg_state {
const struct addr_marker *marker;
unsigned long lines;
bool to_dmesg;
+ bool check_wx;
+ bool found_wx;
};

struct addr_marker {
@@ -214,6 +216,13 @@ static void note_page(struct seq_file *m, struct pg_state *st,
const char *unit = units;
unsigned long delta;
int width = sizeof(unsigned long) * 2;
+ pgprotval_t pr = pgprot_val(st->current_prot);
+ bool savedmesg = st->to_dmesg;
+
+ if (st->check_wx && (pr & _PAGE_RW) && !(pr & _PAGE_NX)) {
+ st->to_dmesg = true;
+ st->found_wx = true;
+ }

/*
* Now print the actual finished series
@@ -261,6 +270,7 @@ static void note_page(struct seq_file *m, struct pg_state *st,
st->start_address = st->current_address;
st->current_prot = new_prot;
st->level = level;
+ st->to_dmesg = savedmesg;
}
}

@@ -344,7 +354,8 @@ static void walk_pud_level(struct seq_file *m, struct pg_state *st, pgd_t addr,
#define pgd_none(a) pud_none(__pud(pgd_val(a)))
#endif

-void ptdump_walk_pgd_level(struct seq_file *m, pgd_t *pgd)
+static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
+ bool checkwx)
{
#ifdef CONFIG_X86_64
pgd_t *start = (pgd_t *) &init_level4_pgt;
@@ -359,6 +370,12 @@ void ptdump_walk_pgd_level(struct seq_file *m, pgd_t *pgd)
st.to_dmesg = true;
}

+ st.check_wx = checkwx;
+ if (checkwx) {
+ pr_info("Checking for W+x mappings\n");
+ st.found_wx = false;
+ }
+
for (i = 0; i < PTRS_PER_PGD; i++) {
st.current_address = normalize_addr(i * PGD_LEVEL_MULT);
if (!pgd_none(*start)) {
@@ -378,6 +395,18 @@ void ptdump_walk_pgd_level(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);
+ if (checkwx && st.found_wx)
+ pr_warn("Found W+x mappings. Please fix.\n");
+}
+
+void ptdump_walk_pgd_level(struct seq_file *m, pgd_t *pgd)
+{
+ ptdump_walk_pgd_level_core(m, pgd, false);
+}
+
+void ptdump_walk_pgd_level_checkwx(void)
+{
+ ptdump_walk_pgd_level_core(NULL, NULL, true);
}

static int ptdump_show(struct seq_file *m, void *v)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index df48430..7e704da 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1150,6 +1150,8 @@ void mark_rodata_ro(void)
free_init_pages("unused kernel",
(unsigned long) __va(__pa_symbol(rodata_end)),
(unsigned long) __va(__pa_symbol(_sdata)));
+
+ ptdump_walk_pgd_level_checkwx();
}

#endif
--
2.1.0