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

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Message-Id: <954181ecfaf0db395348347fa00c419e9f0d41bc.1492596044.git.christophe.leroy@c-s.fr>
Date:   Wed, 19 Apr 2017 13:00:01 +0200 (CEST)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 2/3] powerpc/mm: Fix kernel RAM protection after freeing
 unused memory on PPC32

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@....fr>
---
 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