From a8e53c151fe7ac52a1c13a6ace0c9e8e0f61260c Mon Sep 17 00:00:00 2001 From: Jinbum Park Date: Tue, 12 Dec 2017 01:43:57 +0100 Subject: ARM: 8737/1: mm: dump: add checking for writable and executable Page mappings with full RWX permissions are a security risk. x86, arm64 has an option to walk the page tables and dump any bad pages. (1404d6f13e47 ("arm64: dump: Add checking for writable and exectuable pages")) Add a similar implementation for arm. Reviewed-by: Kees Cook Tested-by: Laura Abbott Reviewed-by: Laura Abbott Signed-off-by: Jinbum Park Signed-off-by: Russell King --- arch/arm/mm/dump.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++- arch/arm/mm/init.c | 2 ++ 2 files changed, 59 insertions(+), 1 deletion(-) (limited to 'arch/arm/mm') diff --git a/arch/arm/mm/dump.c b/arch/arm/mm/dump.c index 43a2beedbbf3..084779c5c893 100644 --- a/arch/arm/mm/dump.c +++ b/arch/arm/mm/dump.c @@ -52,6 +52,8 @@ struct pg_state { unsigned long start_address; unsigned level; u64 current_prot; + bool check_wx; + unsigned long wx_pages; const char *current_domain; }; @@ -60,6 +62,8 @@ struct prot_bits { u64 val; const char *set; const char *clear; + bool ro_bit; + bool nx_bit; }; static const struct prot_bits pte_bits[] = { @@ -73,11 +77,13 @@ static const struct prot_bits pte_bits[] = { .val = L_PTE_RDONLY, .set = "ro", .clear = "RW", + .ro_bit = true, }, { .mask = L_PTE_XN, .val = L_PTE_XN, .set = "NX", .clear = "x ", + .nx_bit = true, }, { .mask = L_PTE_SHARED, .val = L_PTE_SHARED, @@ -141,11 +147,13 @@ static const struct prot_bits section_bits[] = { .val = L_PMD_SECT_RDONLY | PMD_SECT_AP2, .set = "ro", .clear = "RW", + .ro_bit = true, #elif __LINUX_ARM_ARCH__ >= 6 { .mask = PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE, .val = PMD_SECT_APX | PMD_SECT_AP_WRITE, .set = " ro", + .ro_bit = true, }, { .mask = PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE, .val = PMD_SECT_AP_WRITE, @@ -164,6 +172,7 @@ static const struct prot_bits section_bits[] = { .mask = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE, .val = 0, .set = " ro", + .ro_bit = true, }, { .mask = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE, .val = PMD_SECT_AP_WRITE, @@ -182,6 +191,7 @@ static const struct prot_bits section_bits[] = { .val = PMD_SECT_XN, .set = "NX", .clear = "x ", + .nx_bit = true, }, { .mask = PMD_SECT_S, .val = PMD_SECT_S, @@ -194,6 +204,8 @@ struct pg_level { const struct prot_bits *bits; size_t num; u64 mask; + const struct prot_bits *ro_bit; + const struct prot_bits *nx_bit; }; static struct pg_level pg_level[] = { @@ -226,6 +238,23 @@ static void dump_prot(struct pg_state *st, const struct prot_bits *bits, size_t } } +static void note_prot_wx(struct pg_state *st, unsigned long addr) +{ + if (!st->check_wx) + return; + if ((st->current_prot & pg_level[st->level].ro_bit->mask) == + pg_level[st->level].ro_bit->val) + return; + if ((st->current_prot & pg_level[st->level].nx_bit->mask) == + pg_level[st->level].nx_bit->val) + return; + + WARN_ONCE(1, "arm/mm: Found insecure W+X mapping at address %pS\n", + (void *)st->start_address); + + st->wx_pages += (addr - st->start_address) / PAGE_SIZE; +} + static void note_page(struct pg_state *st, unsigned long addr, unsigned int level, u64 val, const char *domain) { @@ -244,6 +273,7 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned long delta; if (st->current_prot) { + note_prot_wx(st, addr); pt_dump_seq_printf(st->seq, "0x%08lx-0x%08lx ", st->start_address, addr); @@ -367,6 +397,7 @@ void ptdump_walk_pgd(struct seq_file *m, struct ptdump_info *info) struct pg_state st = { .seq = m, .marker = info->markers, + .check_wx = false, }; walk_pgd(&st, info->mm, info->base_addr); @@ -379,8 +410,13 @@ static void ptdump_initialize(void) for (i = 0; i < ARRAY_SIZE(pg_level); i++) if (pg_level[i].bits) - for (j = 0; j < pg_level[i].num; j++) + for (j = 0; j < pg_level[i].num; j++) { pg_level[i].mask |= pg_level[i].bits[j].mask; + if (pg_level[i].bits[j].ro_bit) + pg_level[i].ro_bit = &pg_level[i].bits[j]; + if (pg_level[i].bits[j].nx_bit) + pg_level[i].nx_bit = &pg_level[i].bits[j]; + } address_markers[2].start_address = VMALLOC_START; } @@ -391,6 +427,26 @@ static struct ptdump_info kernel_ptdump_info = { .base_addr = 0, }; +void ptdump_check_wx(void) +{ + struct pg_state st = { + .seq = NULL, + .marker = (struct addr_marker[]) { + { 0, NULL}, + { -1, NULL}, + }, + .check_wx = true, + }; + + walk_pgd(&st, &init_mm, 0); + note_page(&st, 0, 0, 0, NULL); + if (st.wx_pages) + pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found\n", + st.wx_pages); + else + pr_info("Checked W+X mappings: passed, no W+X pages found\n"); +} + static int ptdump_init(void) { ptdump_initialize(); diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index a1f11a7ee81b..bd6f4513539a 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include @@ -738,6 +739,7 @@ static int __mark_rodata_ro(void *unused) void mark_rodata_ro(void) { stop_machine(__mark_rodata_ro, NULL, NULL); + debug_checkwx(); } void set_kernel_text_rw(void) -- cgit v1.2.3