[PATCH v2 2/3] powerpc/mm: Fix kernel RAM protection after freeing unused memory on PPC32

Christophe Leroy
2017-04-21T13:02:24Z

As seen below, allthough the init sections have been freed, the
associated memory area is still marked as executable in the
page tables.

~ dmesg
[ 5.860093] Freeing unused kernel memory: 592K (c0570000 - c0604000)

~ cat /sys/kernel/debug/kernel_page_tables
---[ Start of kernel VM ]---
0xc0000000-0xc0497fff 4704K rw X present dirty accessed shared
0xc0498000-0xc056ffff 864K rw present dirty accessed shared
0xc0570000-0xc059ffff 192K rw X present dirty accessed shared
0xc05a0000-0xc7ffffff 125312K rw present dirty accessed shared
---[ vmalloc() Area ]---

This patch fixes that.

The implementation is done by reusing the change_page_attr()
function implemented for CONFIG_DEBUG_PAGEALLOC

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
v2: No change

arch/powerpc/mm/mem.c | 1 +
arch/powerpc/mm/mmu_decl.h | 3 +++
arch/powerpc/mm/pgtable_32.c | 13 ++++++++++---
3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 9ee536ec0739..f261dac36a68 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -401,6 +401,7 @@ void free_initmem(void)
{
ppc_md.progress = ppc_printk_progress;
free_initmem_default(POISON_FREE_INITMEM);
+ remap_init_ram();
}

#ifdef CONFIG_BLK_DEV_INITRD
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index f988db655e5b..718fa45310be 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -95,6 +95,7 @@ extern void _tlbia(void);

extern void mapin_ram(void);
extern int map_page(unsigned long va, phys_addr_t pa, int flags);
+void remap_init_ram(void);
extern void setbat(int index, unsigned long virt, phys_addr_t phys,
unsigned int size, pgprot_t prot);

@@ -106,6 +107,8 @@ struct hash_pte;
extern struct hash_pte *Hash, *Hash_end;
extern unsigned long Hash_size, Hash_mask;

+#else
+static inline void remap_init_ram(void) {}
#endif /* CONFIG_PPC32 */

extern unsigned long ioremap_bot;
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index 8e8940fad12f..31728f3cdd20 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -323,8 +323,6 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
return(retval);
}

-#ifdef CONFIG_DEBUG_PAGEALLOC
-
static int __change_page_attr_noflush(struct page *page, pgprot_t prot)
{
pte_t *kpte;
@@ -347,7 +345,7 @@ static int __change_page_attr_noflush(struct page *page, pgprot_t prot)
/*
* Change the page attributes of an page in the linear mapping.
*
- * THIS CONFLICTS WITH BAT MAPPINGS, DEBUG USE ONLY
+ * THIS DOES NOTHING WITH BAT MAPPINGS, DEBUG USE ONLY
*/
static int change_page_attr(struct page *page, int numpages, pgprot_t prot)
{
@@ -368,7 +366,16 @@ static int change_page_attr(struct page *page, int numpages, pgprot_t prot)
return err;
}

+void remap_init_ram(void)
+{
+ struct page *page = virt_to_page(_sinittext);
+ unsigned long numpages = PFN_UP((unsigned long)_einittext) -
+ PFN_DOWN((unsigned long)_sinittext);
+
+ change_page_attr(page, numpages, PAGE_KERNEL);
+}

+#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
if (PageHighMem(page))
--
2.12.0